serve

11 files changed, 4726 insertions, 0 deletions

@@ -0,0 +1,13 @@
+// This is a manifest file that'll be compiled into application.js, which will include all the files
+// listed below.
+//
+// Any JavaScript/Coffee file within this directory, lib/assets/javascripts, vendor/assets/javascripts,
+// or any plugin's vendor/assets/javascripts directory can be referenced here using a relative path.
+//
+// It's not advisable to add code directly here, but if you do, it'll appear at the bottom of the
+// compiled file. JavaScript code in this file should be added after the last require_* statement.
+//
+// Read Sprockets README (https://github.com/rails/sprockets#sprockets-directives) for details
+// about supported directives.
+//
+//= require_tree .
@@ -0,0 +1,201 @@
+namespace(function() {
+
+function isCellBridgePathFriendly(puzzle, color, pos) {
+  if (pos.x%2 === 0 && pos.y%2 === 0) return false
+  var cell = puzzle.getCell(pos.x, pos.y)
+  return cell == null || cell.color == null || cell.color === color
+}
+
+function makeMinimalTree(graph, root, required) {
+  var seen = Array(graph.length).fill(false)
+  var result = Array(graph.length).fill(false)
+  result[root] = true
+  function dfs(node) {
+    seen[node] = true
+    result[node] = required[node]
+    for (var child of graph[node]) {
+      if (!seen[child]) {
+        dfs(child)
+        result[node] = result[node] || result[child]
+      }
+    }
+  }
+  dfs(root)
+  return result
+}
+
+function isTreeUnique(graph, isInTree) {
+  var seen = isInTree.slice()
+  function dfs(node) {
+    seen[node] = true
+    var reachableTreeNode = null
+    for (var child of graph[node]) {
+      var candidate = null
+      if (isInTree[child]) {
+        candidate = child
+      } else if (!seen[child]) {
+        candidate = dfs(child)
+      }
+      if (candidate != null && candidate !== reachableTreeNode) {
+        if (reachableTreeNode == null) {
+          reachableTreeNode = candidate
+        } else {
+          return -1
+        }
+      }
+    }
+    return reachableTreeNode
+  }
+  for (var i = 0; i < graph.length; i++) {
+    if (!seen[i]) {
+      if (dfs(i) === -1) return false
+    }
+  }
+  return true
+}
+
+function puzzleCellsAdjacent(first, second, pillar) {
+  if (pillar && first.y == second.y && Math.abs(second.x - first.x) === puzzle.width - 1)
+    return true
+  return Math.abs(second.x - first.x) + Math.abs(second.y - first.y) === 1
+}
+
+function bridgeTest(region, puzzle, color, bridges) {
+  var nodes = region.cells.filter(pos => isCellBridgePathFriendly(puzzle, color, pos))
+  var graph = Array.from(Array(nodes.length), () => [])
+  for (var ir = 1; ir < nodes.length; ir++) {
+    var right = nodes[ir]
+    for (var il = 0; il < ir; il++) {
+      var left = nodes[il]
+      if (puzzleCellsAdjacent(left, right, puzzle.pillar)) {
+        graph[il].push(ir)
+        graph[ir].push(il)
+      }
+    }
+  }
+  var isBridge = nodes.map(node => bridges.some(bridge => node.x === bridge.x && node.y === bridge.y))
+  var isInTree = makeMinimalTree(graph, isBridge.indexOf(true), isBridge)
+  for (var i = 0; i < nodes.length; i++) {
+    if (isBridge[i] && !isInTree[i]) return false
+  }
+  return isTreeUnique(graph, isInTree)
+}
+
+window.validateBridges = function(puzzle, region, regionData) {
+  var bridges = {}
+  for (var pos of region) {
+    var cell = puzzle.getCell(pos.x, pos.y)
+    if (cell == null) continue
+
+    // Count color-based elements
+    if (cell.color != null) {
+      if (cell.type === 'bridge') {
+        if (bridges[cell.color] == null) {
+          bridges[cell.color] = []
+        }
+        bridges[cell.color].push(pos)
+      }
+    }
+  }
+
+  for (var color in bridges) {
+    var total = 0
+    var discardable = 0
+    for (var x=1; x < puzzle.width; x+=2) {
+      for (var y=1; y < puzzle.height; y+=2) {
+        var cell = puzzle.getCell(x, y)
+        if (cell != null) {
+          if (cell.type === 'bridge' && cell.color === color) total++
+          if (cell.type === 'nega') discardable++
+        }
+      }
+    }
+
+    if (bridges[color].length != total) {
+      if (bridges[color].length >= total - discardable) {
+        // TODO: Negations in other regions can validate the solution
+        for (var bridge of bridges[color]) {
+          regionData.addInvalid(bridge)
+        }
+      } else {
+        for (var bridge of bridges[color]) {
+          regionData.addVeryInvalid(bridge)
+        }
+      }
+    } else if (!window.bridgeTest(region, puzzle, color, bridges[color])) {
+      for (var bridge of bridges[color]) {
+        regionData.addInvalid(bridge)
+      }
+    }
+  }
+}
+
+var DIRECTIONS = [
+  {'x': 0, 'y':-1},
+  {'x': 1, 'y':-1},
+  {'x': 1, 'y': 0},
+  {'x': 1, 'y': 1},
+  {'x': 0, 'y': 1},
+  {'x':-1, 'y': 1},
+  {'x':-1, 'y': 0},
+  {'x':-1, 'y':-1},
+]
+
+window.validateArrows = function(puzzle, region, regionData) {
+  for (var pos of region) {
+    var cell = puzzle.getCell(pos.x, pos.y)
+    if (cell == null) continue
+    if (cell.type != 'arrow') continue
+    dir = DIRECTIONS[cell.rot]
+
+    var count = 0
+    var x = pos.x + dir.x
+    var y = pos.y + dir.y
+    for (var i=0; i<100; i++) { // 100 is arbitrary, it's just here to avoid infinite loops.
+      var line = puzzle.getLine(x, y)
+      console.spam('Testing', x, y, 'for arrow at', pos.x, pos.y, 'found', line)
+      if (line == null && (x%2 !== 1 || y%2 !== 1)) break
+      if (line > window.LINE_NONE) count++
+      if (count > cell.count) break
+      x += dir.x * 2
+      y += dir.y * 2
+      if (puzzle.matchesSymmetricalPos(x, y, pos.x + dir.x, pos.y + dir.y)) break // Pillar exit condition (in case of looping)
+    }
+    if (count !== cell.count) {
+      console.log('Arrow at', pos.x, pos.y, 'crosses', count, 'lines, but should cross', cell.count)
+      regionData.addInvalid(pos)
+    }
+  }
+}
+
+window.validateSizers = function(puzzle, region, regionData) {
+  var sizers = []
+  var regionSize = 0
+  for (var pos of region) {
+    if (pos.x%2 === 1 && pos.y%2 === 1) regionSize++ // Only count cells for the region
+    var cell = puzzle.getCell(pos.x, pos.y)
+    if (cell == null) continue
+    if (cell.type == 'sizer') sizers.push(pos)
+  }
+  console.debug('Found', sizers.length, 'sizers')
+  if (sizers.length == 0) return // No sizers -- no impact on sizer validity
+
+  var sizerCount = regionSize / sizers.length
+  if (sizerCount % 1 != 0) {
+    console.log('Region size', regionSize, 'is not a multiple of # sizers', sizers.length)
+    for (var sizer of sizers) {
+      regionData.addInvalid(sizer)
+    }
+    return
+  }
+
+  if (puzzle.sizerCount == null) puzzle.sizerCount = sizerCount // No other sizes have been defined
+  if (puzzle.sizerCount != sizerCount) {
+    console.log('sizerCount', sizerCount, 'does not match puzzle sizerCount', puzzle.sizerCount)
+    for (var sizer of sizers) {
+      regionData.addInvalid(sizer)
+    }
+  }
+}
+
+})
@@ -0,0 +1,299 @@
+namespace(function() {
+
+window.draw = function(puzzle, target='puzzle') {
+  if (puzzle == null) return
+  var svg = document.getElementById(target)
+  console.info('Drawing', puzzle, 'into', svg)
+  while (svg.firstChild) svg.removeChild(svg.firstChild)
+
+  // Prevent context menu popups within the puzzle
+  svg.oncontextmenu = function(event) {
+    event.preventDefault()
+  }
+
+  if (puzzle.pillar === true) {
+    // 41*width + 30*2 (padding) + 10*2 (border)
+    var pixelWidth = 41 * puzzle.width + 80
+  } else {
+    // 41*(width-1) + 24 (extra edge) + 30*2 (padding) + 10*2 (border)
+    var pixelWidth = 41 * puzzle.width + 63
+  }
+  var pixelHeight = 41 * puzzle.height + 63
+  svg.setAttribute('viewbox', '0 0 ' + pixelWidth + ' ' + pixelHeight)
+  svg.setAttribute('width', pixelWidth)
+  svg.setAttribute('height', pixelHeight)
+
+  var rect = createElement('rect')
+  svg.appendChild(rect)
+  rect.setAttribute('stroke-width', 10)
+  rect.setAttribute('stroke', window.BORDER)
+  rect.setAttribute('fill', window.OUTER_BACKGROUND)
+  // Accounting for the border thickness
+  rect.setAttribute('x', 5)
+  rect.setAttribute('y', 5)
+  rect.setAttribute('width', pixelWidth - 10) // Removing border
+  rect.setAttribute('height', pixelHeight - 10) // Removing border
+
+  drawCenters(puzzle, svg)
+  drawGrid(puzzle, svg, target)
+  drawStartAndEnd(puzzle, svg)
+  // Draw cell symbols after so they overlap the lines, if necessary
+  drawSymbols(puzzle, svg, target)
+
+  // For pillar puzzles, add faders for the left and right sides
+  if (puzzle.pillar === true) {
+    var defs = window.createElement('defs')
+    defs.id = 'cursorPos'
+    defs.innerHTML = '' +
+    '<linearGradient id="fadeInLeft">\n' +
+    '  <stop offset="0%"   stop-opacity="1.0" stop-color="' + window.OUTER_BACKGROUND + '"></stop>\n' +
+    '  <stop offset="25%"  stop-opacity="1.0" stop-color="' + window.OUTER_BACKGROUND + '"></stop>\n' +
+    '  <stop offset="100%" stop-opacity="0.0" stop-color="' + window.OUTER_BACKGROUND + '"></stop>\n' +
+    '</linearGradient>\n' +
+    '<linearGradient id="fadeOutRight">\n' +
+    '  <stop offset="0%"   stop-opacity="0.0" stop-color="' + window.OUTER_BACKGROUND + '"></stop>\n' +
+    '  <stop offset="100%" stop-opacity="1.0" stop-color="' + window.OUTER_BACKGROUND + '"></stop>\n' +
+    '</linearGradient>\n'
+    svg.appendChild(defs)
+
+    var leftBox = window.createElement('rect')
+    leftBox.setAttribute('x', 16)
+    leftBox.setAttribute('y', 10)
+    leftBox.setAttribute('width', 48)
+    leftBox.setAttribute('height', 41 * puzzle.height + 43)
+    leftBox.setAttribute('fill', 'url(#fadeInLeft)')
+    leftBox.setAttribute('style', 'pointer-events: none')
+    svg.appendChild(leftBox)
+
+    var rightBox = window.createElement('rect')
+    rightBox.setAttribute('x', 41 * puzzle.width + 22)
+    rightBox.setAttribute('y', 10)
+    rightBox.setAttribute('width', 30)
+    rightBox.setAttribute('height', 41 * puzzle.height + 43)
+    rightBox.setAttribute('fill', 'url(#fadeOutRight)')
+    rightBox.setAttribute('style', 'pointer-events: none')
+    svg.appendChild(rightBox)
+  }
+}
+
+function drawCenters(puzzle, svg) {
+  // @Hack that I am not fixing. This switches the puzzle's grid to a floodfilled grid
+  // where null represents cells which are part of the outside
+  var savedGrid = puzzle.switchToMaskedGrid()
+  if (puzzle.pillar === true) {
+    for (var y=1; y<puzzle.height; y += 2) {
+      if (puzzle.getCell(-1, y) == null) continue // Cell borders the outside
+
+      var rect = createElement('rect')
+      rect.setAttribute('x', 28)
+      rect.setAttribute('y', 41 * y + 11)
+      rect.setAttribute('width', 24)
+      rect.setAttribute('height', 82)
+      rect.setAttribute('fill', window.BACKGROUND)
+      svg.appendChild(rect)
+    }
+  }
+
+  for (var x=1; x<puzzle.width; x += 2) {
+    for (var y=1; y<puzzle.height; y += 2) {
+      if (puzzle.grid[x][y] == null) continue // Cell borders the outside
+
+      var rect = createElement('rect')
+      rect.setAttribute('x', 41 * x + 11)
+      rect.setAttribute('y', 41 * y + 11)
+      rect.setAttribute('width', 82)
+      rect.setAttribute('height', 82)
+      rect.setAttribute('fill', window.BACKGROUND)
+      rect.setAttribute('shape-rendering', 'crispedges') // Otherwise they don't meet behind gaps
+      svg.appendChild(rect)
+    }
+  }
+  puzzle.grid = savedGrid
+}
+
+function drawGrid(puzzle, svg, target) {
+  for (var x=0; x<puzzle.width; x++) {
+    for (var y=0; y<puzzle.height; y++) {
+      var cell = puzzle.grid[x][y]
+      if (cell != null && cell.gap === window.GAP_FULL) continue
+      if (cell != null && cell.gap === window.GAP_BREAK) {
+        var params = {
+          'width':58,
+          'height':58,
+          'x': x*41 + 23,
+          'y': y*41 + 23,
+          'class': target + '_' + x + '_' + y,
+          'type': 'gap',
+        }
+        if (x%2 === 0 && y%2 === 1) params.rot = 1
+        drawSymbolWithSvg(svg, params)
+        continue
+      }
+
+      var line = createElement('line')
+      line.setAttribute('stroke-width', 24)
+      line.setAttribute('stroke-linecap', 'round')
+      line.setAttribute('stroke', window.FOREGROUND)
+      if (x%2 === 1 && y%2 === 0) { // Horizontal
+        if (cell.gap === window.GAP_BREAK) continue
+        line.setAttribute('x1', (x-1)*41 + 52)
+        // Adjust the length if it's a pillar -- the grid is not as wide!
+        if (puzzle.pillar === true && x === puzzle.width - 1) {
+          line.setAttribute('x2', (x+1)*41 + 40)
+        } else {
+          line.setAttribute('x2', (x+1)*41 + 52)
+        }
+        line.setAttribute('y1', y*41 + 52)
+        line.setAttribute('y2', y*41 + 52)
+        svg.appendChild(line)
+      } else if (x%2 === 0 && y%2 === 1) { // Vertical
+        if (cell.gap === window.GAP_BREAK) continue
+        line.setAttribute('x1', x*41 + 52)
+        line.setAttribute('x2', x*41 + 52)
+        line.setAttribute('y1', (y-1)*41 + 52)
+        line.setAttribute('y2', (y+1)*41 + 52)
+        svg.appendChild(line)
+      } else if (x%2 === 0 && y%2 === 0) { // Intersection
+        var surroundingLines = 0
+        if (cell.end != null) surroundingLines++
+        var leftCell = puzzle.getCell(x - 1, y)
+        if (leftCell != null && leftCell.gap !== window.GAP_FULL) surroundingLines++
+        var rightCell = puzzle.getCell(x + 1, y)
+        if (rightCell != null && rightCell.gap !== window.GAP_FULL) surroundingLines++
+        var topCell = puzzle.getCell(x, y - 1)
+        if (topCell != null && topCell.gap !== window.GAP_FULL) surroundingLines++
+        var bottomCell = puzzle.getCell(x, y + 1)
+        if (bottomCell != null && bottomCell.gap !== window.GAP_FULL) surroundingLines++
+
+        if (surroundingLines === 1) {
+          // Add square caps for dead ends which are non-endpoints
+          var rect = createElement('rect')
+          rect.setAttribute('x', x*41 + 40)
+          rect.setAttribute('y', y*41 + 40)
+          rect.setAttribute('width', 24)
+          rect.setAttribute('height', 24)
+          rect.setAttribute('fill', window.FOREGROUND)
+          svg.appendChild(rect)
+        } else if (surroundingLines > 1) {
+          // Add rounding for other intersections (handling gap-only corners)
+          var circ = createElement('circle')
+          circ.setAttribute('cx', x*41 + 52)
+          circ.setAttribute('cy', y*41 + 52)
+          circ.setAttribute('r', 12)
+          circ.setAttribute('fill', window.FOREGROUND)
+          svg.appendChild(circ)
+        }
+      }
+    }
+  }
+  // Determine if left-side needs a 'wrap indicator'
+  if (puzzle.pillar === true) {
+    var x = 0;
+    for (var y=0; y<puzzle.height; y+=2) {
+      var cell = puzzle.getCell(x-1, y)
+      if (cell == null || cell.gap === window.GAP_FULL) continue
+      var line = createElement('line')
+      line.setAttribute('stroke-width', 24)
+      line.setAttribute('stroke-linecap', 'round')
+      line.setAttribute('stroke', window.FOREGROUND)
+      line.setAttribute('x1', x*41 + 40)
+      line.setAttribute('x2', x*41 + 52)
+      line.setAttribute('y1', y*41 + 52)
+      line.setAttribute('y2', y*41 + 52)
+      svg.appendChild(line)
+    }
+  }
+}
+
+function drawSymbols(puzzle, svg, target) {
+  for (var x=0; x<puzzle.width; x++) {
+    for (var y=0; y<puzzle.height; y++) {
+      var cell = puzzle.grid[x][y]
+      if (cell == null) continue
+      var params = {
+        'width':58,
+        'height':58,
+        'x': x*41 + 23,
+        'y': y*41 + 23,
+        'class': target + '_' + x + '_' + y,
+      }
+      if (cell.dot > window.DOT_NONE) {
+        params.type = 'dot'
+        if (cell.dot === window.DOT_BLACK) params.color = 'black'
+        else if (cell.dot === window.DOT_BLUE) params.color = window.LINE_PRIMARY
+        else if (cell.dot === window.DOT_YELLOW) params.color = window.LINE_SECONDARY
+        else if (cell.dot === window.DOT_INVISIBLE) {
+          params.color = window.FOREGROUND
+          // This makes the invisible dots visible, but only while we're in the editor.
+          if (document.getElementById('metaButtons') != null) {
+            params.stroke = 'black'
+            params.strokeWidth = '2px'
+          }
+        }
+        drawSymbolWithSvg(svg, params)
+      } else if (cell.gap === window.GAP_BREAK) {
+        // Gaps were handled above, while drawing the grid.
+      } else if (x%2 === 1 && y%2 === 1) {
+        // Generic draw for all other elements
+        Object.assign(params, cell)
+        window.drawSymbolWithSvg(svg, params, puzzle.settings.CUSTOM_MECHANICS)
+      }
+    }
+  }
+}
+
+function drawStartAndEnd(puzzle, svg) {
+  for (var x=0; x<puzzle.width; x++) {
+    for (var y=0; y<puzzle.height; y++) {
+      var cell = puzzle.grid[x][y]
+      if (cell == null) continue
+      if (cell.end != null) {
+        window.drawSymbolWithSvg(svg, {
+          'type': 'end',
+          'width': 58,
+          'height': 58,
+          'dir': cell.end,
+          'x': x*41 + 23,
+          'y': y*41 + 23,
+        })
+      }
+
+      if (cell.start === true) {
+        var symStart = null
+        if (puzzle.symmetry != null) {
+          var sym = puzzle.getSymmetricalPos(x, y)
+          window.drawSymbolWithSvg(svg, {
+            'type': 'start',
+            'width': 58,
+            'height': 58,
+            'x': sym.x*41 + 23,
+            'y': sym.y*41 + 23,
+          })
+          symStart = svg.lastChild
+          symStart.style.display = 'none'
+          symStart.id = 'symStart_' + svg.id + '_' + x + '_' + y
+        }
+
+        window.drawSymbolWithSvg(svg, {
+          'type': 'start',
+          'width': 58,
+          'height': 58,
+          'x': x*41 + 23,
+          'y': y*41 + 23,
+        })
+        var start = svg.lastChild
+        start.id = 'start_' + svg.id + '_' + x + '_' + y
+
+        // ;(function(a){}(a))
+        // This syntax is used to forcibly copy all of the arguments
+        ;(function(puzzle, x, y, start, symStart) {
+          start.onpointerdown = function(event) {
+            window.trace(event, puzzle, {'x':x, 'y':y}, start, symStart)
+          }
+        }(puzzle, x, y, start, symStart))
+      }
+    }
+  }
+}
+
+})
@@ -0,0 +1,331 @@
+namespace(function() {
+
+function getPolySize(polyshape) {
+  var size = 0
+  for (var x=0; x<4; x++) {
+    for (var y=0; y<4; y++) {
+      if (isSet(polyshape, x, y)) size++
+    }
+  }
+  return size
+}
+
+function mask(x, y) {
+  return 1 << ((3-y)*4 + x)
+}
+
+function isSet(polyshape, x, y) {
+  if (x < 0 || y < 0) return false
+  if (x >= 4 || y >= 4) return false
+  return (polyshape & mask(x, y)) !== 0
+}
+
+// This is 2^20, whereas all the other bits fall into 2^(0-15)
+window.ROTATION_BIT = (1 << 20)
+
+window.isRotated = function(polyshape) {
+  return (polyshape & ROTATION_BIT) !== 0
+}
+
+function getRotations(polyshape) {
+  if (!isRotated(polyshape)) return [polyshape]
+
+  var rotations = [0, 0, 0, 0]
+  for (var x=0; x<4; x++) {
+    for (var y=0; y<4; y++) {
+      if (isSet(polyshape, x, y)) {
+        rotations[0] ^= mask(x, y)
+        rotations[1] ^= mask(y, 3-x)
+        rotations[2] ^= mask(3-x, 3-y)
+        rotations[3] ^= mask(3-y, x)
+      }
+    }
+  }
+
+  return rotations
+}
+
+// 90 degree rotations of the polyomino
+window.rotatePolyshape = function(polyshape, count=1) {
+  var rotations = getRotations(polyshape | window.ROTATION_BIT)
+  return rotations[count % 4]
+}
+
+// IMPORTANT NOTE: When formulating these, the top row must contain (0, 0)
+// That means there will never be any negative y values.
+// (0, 0) must also be a cell in the shape, so that
+// placing the shape at (x, y) will fill (x, y)
+// Ylops will have -1s on all adjacent cells, to break "overlaps" for polyominos.
+window.polyominoFromPolyshape = function(polyshape, ylop=false, precise=true) {
+  var topLeft = null
+  for (var y=0; y<4; y++) {
+    for (var x=0; x<4; x++) {
+      if (isSet(polyshape, x, y)) {
+        topLeft = {'x':x, 'y':y}
+        break
+      }
+    }
+    if (topLeft != null) break
+  }
+  if (topLeft == null) return [] // Empty polyomino
+
+  var polyomino = []
+  for (var x=0; x<4; x++) {
+    for (var y=0; y<4; y++) {
+      if (!isSet(polyshape, x, y)) continue
+      polyomino.push({'x':2*(x - topLeft.x), 'y':2*(y - topLeft.y)})
+
+      // "Precise" polyominos adds cells in between the apparent squares in the polyomino.
+      // This prevents the solution line from going through polyominos in the solution.
+      if (precise) {
+        if (ylop) {
+          // Ylops fill up/left if no adjacent cell, and always fill bottom/right
+          if (!isSet(polyshape, x - 1, y)) {
+            polyomino.push({'x':2*(x - topLeft.x) - 1, 'y':2*(y - topLeft.y)})
+          }
+          if (!isSet(polyshape, x, y - 1)) {
+            polyomino.push({'x':2*(x - topLeft.x), 'y':2*(y - topLeft.y) - 1})
+          }
+          polyomino.push({'x':2*(x - topLeft.x) + 1, 'y':2*(y - topLeft.y)})
+          polyomino.push({'x':2*(x - topLeft.x), 'y':2*(y - topLeft.y) + 1})
+        } else {
+          // Normal polys only fill bottom/right if there is an adjacent cell.
+          if (isSet(polyshape, x + 1, y)) {
+            polyomino.push({'x':2*(x - topLeft.x) + 1, 'y':2*(y - topLeft.y)})
+          }
+          if (isSet(polyshape, x, y + 1)) {
+            polyomino.push({'x':2*(x - topLeft.x), 'y':2*(y - topLeft.y) + 1})
+          }
+        }
+      }
+    }
+  }
+  return polyomino
+}
+
+window.polyshapeFromPolyomino = function(polyomino) {
+  var topLeft = {'x': 9999, 'y': 9999}
+  for (var pos of polyomino) {
+    if (pos.x%2 != 1 || pos.y%2 != 1) continue // We only care about cells, not edges or intersections
+    
+    // Unlike when we're making a polyomino, we just want to top and left flush the shape,
+    // we don't actually need (0, 0) to be filled.
+    if (pos.x < topLeft.x) topLeft.x = pos.x
+    if (pos.y < topLeft.y) topLeft.y = pos.y
+  }
+  if (topLeft == null) return 0 // Empty polyomino
+
+  var polyshape = 0
+  for (var pos of polyomino) {
+    if (pos.x%2 != 1 || pos.y%2 != 1) continue // We only care about cells, not edges or intersections
+    var x = (pos.x - topLeft.x) / 2 // 0.5x to convert from puzzle coordinates to polyshape coordinates
+    var y = (pos.y - topLeft.y) / 2 // 0.5x to convert from puzzle coordinates to polyshape coordinates
+    polyshape |= mask(x, y)
+  }
+  
+  return polyshape
+}
+
+// In some cases, polyominos and onimoylops will fully cancel each other out.
+// However, even if they are the same size, that doesn't guarantee that they fit together.
+// As an optimization, we save the results for known combinations of shapes, since there are likely many
+// fewer pairings of shapes than paths through the grid.
+var knownCancellations = {}
+
+// Attempt to fit polyominos in a region into the puzzle.
+// This function checks for early exits, then simplifies the grid to a numerical representation:
+// * 1 represents a square that has been double-covered (by two polyominos)
+//   * Or, in the cancellation case, it represents a square that was covered by a polyomino and not by an onimoylop
+// * 0 represents a square that is satisfied, either because:
+//   * it is outside the region
+//   * (In the normal case) it was inside the region, and has been covered by a polyomino
+//   * (In the cancellation case) it was covered by an equal number of polyominos and onimoylops
+// * -1 represents a square that needs to be covered once (inside the region, or outside but covered by an onimoylop)
+// * -2 represents a square that needs to be covered twice (inside the region & covered by an onimoylop)
+// * And etc, for additional layers of polyominos/onimoylops.
+window.polyFit = function(region, puzzle) {
+  var polys = []
+  var ylops = []
+  var polyCount = 0
+  var regionSize = 0
+  for (var pos of region) {
+    if (pos.x%2 === 1 && pos.y%2 === 1) regionSize++
+    var cell = puzzle.grid[pos.x][pos.y]
+    if (cell == null) continue
+    if (cell.polyshape === 0) continue
+    if (cell.type === 'poly') {
+      polys.push(cell)
+      polyCount += getPolySize(cell.polyshape)
+    } else if (cell.type === 'ylop') {
+      ylops.push(cell)
+      polyCount -= getPolySize(cell.polyshape)
+    }
+  }
+  if (polys.length + ylops.length === 0) {
+    console.log('No polyominos or onimoylops inside the region, vacuously true')
+    return true
+  }
+  if (polyCount > 0 && polyCount !== regionSize) {
+    console.log('Combined size of polyominos and onimoylops', polyCount, 'does not match region size', regionSize)
+    return false
+  }
+  if (polyCount < 0) {
+    console.log('Combined size of onimoylops is greater than polyominos by', -polyCount)
+    return false
+  }
+  var key = null
+  if (polyCount === 0) {
+    if (puzzle.settings.SHAPELESS_ZERO_POLY) {
+      console.log('Combined size of polyominos and onimoylops is zero')
+      return true
+    }
+    // These will be ordered by the order of cells in the region, which isn't exactly consistent.
+    // In practice, it seems to be good enough.
+    key = ''
+    for (var ylop of ylops) key += ' ' + ylop.polyshape
+    key += '|'
+    for (var poly of polys) key += ' ' + poly.polyshape
+    var ret = knownCancellations[key]
+    if (ret != null) return ret
+  }
+
+  // For polyominos, we clear the grid to mark it up again:
+  var savedGrid = puzzle.grid
+  puzzle.newGrid()
+  // First, we mark all cells as 0: Cells outside the target region should be unaffected.
+  for (var x=0; x<puzzle.width; x++) {
+    for (var y=0; y<puzzle.height; y++) {
+      puzzle.setCell(x, y, 0)
+    }
+  }
+  // In the normal case, we mark every cell as -1: It needs to be covered by one poly
+  if (polyCount > 0) {
+    for (var pos of region) puzzle.grid[pos.x][pos.y] = -1
+  }
+  // In the exact match case, we leave every cell marked 0: Polys and ylops need to cancel.
+
+  var ret = placeYlops(ylops, 0, polys, puzzle)
+  if (polyCount === 0) knownCancellations[key] = ret
+  puzzle.grid = savedGrid
+  return ret
+}
+
+// If false, poly doesn't fit and grid is unmodified
+// If true, poly fits and grid is modified (with the placement)
+function tryPlacePolyshape(cells, x, y, puzzle, sign) {
+  console.spam('Placing at', x, y, 'with sign', sign)
+  var numCells = cells.length
+  for (var i=0; i<numCells; i++) {
+    var cell = cells[i]
+    var puzzleCell = puzzle.getCell(cell.x + x, cell.y + y)
+    if (puzzleCell == null) return false
+    cell.value = puzzleCell
+  }
+  for (var i=0; i<numCells; i++) {
+    var cell = cells[i]
+    puzzle.setCell(cell.x + x, cell.y + y, cell.value + sign)
+  }
+  return true
+}
+
+// Places the ylops such that they are inside of the grid, then checks if the polys
+// zero the region.
+function placeYlops(ylops, i, polys, puzzle) {
+  // Base case: No more ylops to place, start placing polys
+  if (i === ylops.length) return placePolys(polys, puzzle)
+
+  var ylop = ylops[i]
+  var ylopRotations = getRotations(ylop.polyshape)
+  for (var x=1; x<puzzle.width; x+=2) {
+    for (var y=1; y<puzzle.height; y+=2) {
+      console.log('Placing ylop', ylop, 'at', x, y)
+      for (var polyshape of ylopRotations) {
+        var cells = polyominoFromPolyshape(polyshape, true, puzzle.settings.PRECISE_POLYOMINOS)
+        if (!tryPlacePolyshape(cells, x, y, puzzle, -1)) continue
+        console.group('')
+        if (placeYlops(ylops, i+1, polys, puzzle)) return true
+        console.groupEnd('')
+        if (!tryPlacePolyshape(cells, x, y, puzzle, +1)) continue
+      }
+    }
+  }
+  console.log('Tried all ylop placements with no success.')
+  return false
+}
+
+// Returns whether or not a set of polyominos fit into a region.
+// Solves via recursive backtracking: Some piece must fill the top left square,
+// so try every piece to fill it, then recurse.
+function placePolys(polys, puzzle) {
+  // Check for overlapping polyominos, and handle exit cases for all polyominos placed.
+  var allPolysPlaced = (polys.length === 0)
+  for (var x=0; x<puzzle.width; x++) {
+    var row = puzzle.grid[x]
+    for (var y=0; y<puzzle.height; y++) {
+      var cell = row[y]
+      if (cell > 0) {
+        console.log('Cell', x, y, 'has been overfilled and no ylops left to place')
+        return false
+      }
+      if (allPolysPlaced && cell < 0 && x%2 === 1 && y%2 === 1) {
+        // Normal, center cell with a negative value & no polys remaining.
+        console.log('All polys placed, but grid not full')
+        return false
+      }
+    }
+  }
+  if (allPolysPlaced) {
+    console.log('All polys placed, and grid full')
+    return true
+  }
+
+  // The top-left (first open cell) must be filled by a polyomino.
+  // However in the case of pillars, there is no top-left, so we try all open cells in the
+  // top-most open row
+  var openCells = []
+  for (var y=1; y<puzzle.height; y+=2) {
+    for (var x=1; x<puzzle.width; x+=2) {
+      if (puzzle.grid[x][y] >= 0) continue
+      openCells.push({'x':x, 'y':y})
+      if (puzzle.pillar === false) break
+    }
+    if (openCells.length > 0) break
+  }
+
+  if (openCells.length === 0) {
+    console.log('Polys remaining but grid full')
+    return false
+  }
+
+  for (var openCell of openCells) {
+    var attemptedPolyshapes = []
+    for (var i=0; i<polys.length; i++) {
+      var poly = polys[i]
+      console.spam('Selected poly', poly)
+      if (attemptedPolyshapes.includes(poly.polyshape)) {
+        console.spam('Polyshape', poly.polyshape, 'has already been attempted')
+        continue
+      }
+      attemptedPolyshapes.push(poly.polyshape)
+      polys.splice(i, 1)
+      for (var polyshape of getRotations(poly.polyshape)) {
+        console.spam('Selected polyshape', polyshape)
+        var cells = polyominoFromPolyshape(polyshape, false, puzzle.settings.PRECISE_POLYOMINOS)
+        if (!tryPlacePolyshape(cells, openCell.x, openCell.y, puzzle, +1)) {
+          console.spam('Polyshape', polyshape, 'does not fit into', openCell.x, openCell.y)
+          continue
+        }
+        console.group('')
+        if (placePolys(polys, puzzle)) return true
+        console.groupEnd('')
+        // Should not fail, as it's an inversion of the above tryPlacePolyshape
+        tryPlacePolyshape(cells, openCell.x, openCell.y, puzzle, -1)
+      }
+      polys.splice(i, 0, poly)
+    }
+  }
+  console.log('Grid non-empty with >0 polys, but no valid recursion.')
+  return false
+}
+
+})
@@ -0,0 +1,507 @@
+namespace(function() {
+
+// A 2x2 grid is internally a 5x5:
+// corner, edge, corner, edge, corner
+// edge,   cell, edge,   cell, edge
+// corner, edge, corner, edge, corner
+// edge,   cell, edge,   cell, edge
+// corner, edge, corner, edge, corner
+//
+// Corners and edges will have a value of true if the line passes through them
+// Cells will contain an object if there is an element in them
+window.Puzzle = class {
+  constructor(width, height, pillar=false) {
+    if (pillar === true) {
+      this.newGrid(2 * width, 2 * height + 1)
+    } else {
+      this.newGrid(2 * width + 1, 2 * height + 1)
+    }
+    this.pillar = pillar
+    this.settings = {
+      // If true, negation symbols are allowed to cancel other negation symbols.
+      NEGATIONS_CANCEL_NEGATIONS: true,
+
+      // If true, and the count of polyominos and onimoylops is zero, they cancel regardless of shape.
+      SHAPELESS_ZERO_POLY: false,
+
+      // If true, the traced line cannot go through the placement of a polyomino.
+      PRECISE_POLYOMINOS: true,
+
+      // If false, incorrect elements will not flash when failing the puzzle.
+      FLASH_FOR_ERRORS: true,
+
+      // If true, mid-segment startpoints will constitute solid lines, and form boundaries for the region.
+      FAT_STARTPOINTS: false,
+
+      // If true, custom mechanics are displayed (and validated) in this puzzle.
+      CUSTOM_MECHANICS: false,
+      
+      // If true, polyominos may be placed partially off of the grid as an intermediate solution step.
+      // OUT_OF_BOUNDS_POLY: false,
+    }
+  }
+
+  static deserialize(json) {
+    var parsed = JSON.parse(json)
+    // Claim that it's not a pillar (for consistent grid sizing), then double-check ourselves later.
+    var puzzle = new Puzzle((parsed.grid.length - 1)/2, (parsed.grid[0].length - 1)/2)
+    puzzle.name = parsed.name
+    puzzle.autoSolved = parsed.autoSolved
+    puzzle.grid = parsed.grid
+    // Legacy: Grid squares used to use 'false' to indicate emptiness.
+    // Legacy: Cells may use {} to represent emptiness
+    // Now, we use:
+    // Cells default to null
+    // During onTraceStart, empty cells that are still inbounds are changed to {'type': 'nonce'} for tracing purposes.
+    // Lines default to {'type':'line', 'line':0}
+    for (var x=0; x<puzzle.width; x++) {
+      for (var y=0; y<puzzle.height; y++) {
+        var cell = puzzle.grid[x][y]
+        if (cell === false || cell == null || cell.type == null) {
+          if (x%2 === 1 && y%2 === 1) puzzle.grid[x][y] = null
+          else puzzle.grid[x][y] = {'type':'line', 'line':window.LINE_NONE}
+        } else {
+          if (cell.type === 'poly' || cell.type === 'ylop') {
+            if (cell.rot === 'all') {
+              // Legacy: Polys and ylops used to have a rot value (before I started using polyshape).
+              // rot=all is a holdover that was used to represent rotation polyominos.
+              puzzle.grid[x][y].polyshape |= window.ROTATION_BIT
+              delete puzzle.grid[x][y].rot
+            }
+            // Fixup: Sometimes we have a polyshape which is empty. Just ignore these objects.
+            if (puzzle.grid[x][y].polyshape & ~window.ROTATION_BIT === 0) puzzle.grid[x][y] = null
+          } else if ((x%2 !== 1 || y%2 !== 1) && cell.color != null) {
+            // Legacy: Lines used to use 'color' instead of 'line', but that was redundant with actual colors
+            cell.line = cell.color
+            delete cell.color
+          } else if (cell.gap === true) {
+            // Legacy: Gaps used to be null/true, are now null/1/2
+            puzzle.grid[x][y].gap = window.GAP_BREAK
+          }
+        }
+      }
+    }
+    // Legacy: Startpoints used to be only parsed.start
+    if (parsed.start) {
+      parsed.startPoints = [parsed.start]
+    }
+    // Legacy: Startpoints used to be a separate array, now they are flags
+    if (parsed.startPoints) {
+      for (var startPoint of parsed.startPoints) {
+        puzzle.grid[startPoint.x][startPoint.y].start = true
+      }
+    }
+    // Legacy: Endpoints used to be only parsed.end
+    if (parsed.end) {
+      parsed.endPoints = [parsed.end]
+    }
+    // Legacy: Endpoints used to be a separate array, now they are flags
+    if (parsed.endPoints) {
+      for (var endPoint of parsed.endPoints) {
+        puzzle.grid[endPoint.x][endPoint.y].end = endPoint.dir
+      }
+    }
+    // Legacy: Dots and gaps used to be separate arrays
+    // Now, they are flags on the individual lines.
+    if (parsed.dots) {
+      for (var dot of parsed.dots) {
+        puzzle.grid[dot.x][dot.y].dot = window.DOT_BLACK
+      }
+    }
+    if (parsed.gaps) {
+      for (var gap of parsed.gaps) {
+        puzzle.grid[gap.x][gap.y].gap = window.GAP_BREAK
+      }
+    }
+    if (parsed.settings) {
+      for (var key of Object.keys(parsed.settings)) {
+        puzzle.settings[key] = parsed.settings[key]
+      }
+    }
+    puzzle.pillar = parsed.pillar
+    puzzle.symmetry = parsed.symmetry
+    puzzle.largezero = puzzle.width * puzzle.height
+    return puzzle
+  }
+
+  serialize() {
+    return JSON.stringify(this)
+  }
+
+  clone() {
+    return Puzzle.deserialize(this.serialize())
+  }
+
+  // This is explicitly *not* just clearing the grid, so that external references
+  // to the grid are not also cleared.
+  newGrid(width, height) {
+    if (width == null) { // Called by someone who just wants to clear the grid.
+      width = this.width
+      height = this.height
+    }
+    this.grid = []
+    for (var x=0; x<width; x++) {
+      this.grid[x] = []
+      for (var y=0; y<height; y++) {
+        if (x%2 === 1 && y%2 === 1) this.grid[x][y] = null
+        else this.grid[x][y] = {'type':'line', 'line':LINE_NONE}
+      }
+    }
+    // Performance: A large value which is === 0 to be used for pillar wrapping.
+    // Performance: Getting the size of the grid has a nonzero cost.
+    // Definitely getting the length of the first element isn't optimized.
+    this.largezero = width * height * 2
+    this.width = this.grid.length
+    this.height = this.grid[0].length
+  }
+
+  // Wrap a value around at the width of the grid. No-op if not in pillar mode.
+  _mod(val) {
+    if (this.pillar === false) return val
+    return (val + this.largezero) % this.width
+  }
+
+  // Determine if an x, y pair is a safe reference inside the grid. This should be invoked at the start of every
+  // function, but then functions can access the grid directly.
+  _safeCell(x, y) {
+    if (x < 0 || x >= this.width) return false
+    if (y < 0 || y >= this.height) return false
+    return true
+  }
+
+  getCell(x, y) {
+    x = this._mod(x)
+    if (!this._safeCell(x, y)) return null
+    return this.grid[x][y]
+  }
+
+  setCell(x, y, value) {
+    x = this._mod(x)
+    if (!this._safeCell(x, y)) return
+    this.grid[x][y] = value
+  }
+
+  getSymmetricalDir(dir) {
+    if (this.symmetry != null) {
+      if (this.symmetry.x === true) {
+        if (dir === 'left') return 'right'
+        if (dir === 'right') return 'left'
+      }
+      if (this.symmetry.y === true) {
+        if (dir === 'top') return 'bottom'
+        if (dir === 'bottom') return 'top'
+      }
+    }
+    return dir
+  }
+
+  // The resulting position is guaranteed to be gridsafe.
+  getSymmetricalPos(x, y) {
+    if (this.symmetry != null) {
+      if (this.pillar === true) {
+        x += this.width/2
+        if (this.symmetry.x === true) {
+          x = this.width - x
+        }
+      } else {
+        if (this.symmetry.x === true) {
+          x = (this.width - 1) - x
+        }
+      }
+      if (this.symmetry.y === true) {
+        y = (this.height - 1) - y
+      }
+    }
+    return {'x':this._mod(x), 'y':y}
+  }
+
+  getSymmetricalCell(x, y) {
+    var pos = this.getSymmetricalPos(x, y)
+    return this.getCell(pos.x, pos.y)
+  }
+
+  matchesSymmetricalPos(x1, y1, x2, y2) {
+    return (y1 === y2 && this._mod(x1) === x2)
+  }
+
+  // A variant of getCell which specifically returns line values,
+  // and treats objects as being out-of-bounds
+  getLine(x, y) {
+    var cell = this.getCell(x, y)
+    if (cell == null) return null
+    if (cell.type !== 'line') return null
+    return cell.line
+  }
+
+  updateCell2(x, y, key, value) {
+    x = this._mod(x)
+    if (!this._safeCell(x, y)) return
+    var cell = this.grid[x][y]
+    if (cell == null) return
+    cell[key] = value
+  }
+
+  getValidEndDirs(x, y) {
+    x = this._mod(x)
+    if (!this._safeCell(x, y)) return []
+
+    var dirs = []
+    var leftCell = this.getCell(x - 1, y)
+    if (leftCell == null || leftCell.gap === window.GAP_FULL) dirs.push('left')
+    var topCell = this.getCell(x, y - 1)
+    if (topCell == null || topCell.gap === window.GAP_FULL) dirs.push('top')
+    var rightCell = this.getCell(x + 1, y)
+    if (rightCell == null || rightCell.gap === window.GAP_FULL) dirs.push('right')
+    var bottomCell = this.getCell(x, y + 1)
+    if (bottomCell == null || bottomCell.gap === window.GAP_FULL) dirs.push('bottom')
+    return dirs
+  }
+
+  // Note: Does not use this.width/this.height, so that it may be used to ask about resizing.
+  getSizeError(width, height) {
+    if (this.pillar && width < 4) return 'Pillars may not have a width of 1'
+    if (width * height < 25) return 'Puzzles may not be smaller than 2x2 or 1x4'
+    if (width > 21 || height > 21) return 'Puzzles may not be larger than 10 in either dimension'
+    if (this.symmetry != null) {
+      if (this.symmetry.x && width <= 2) return 'Symmetrical puzzles must be sufficiently wide for both lines'
+      if (this.symmetry.y && height <= 2) return 'Symmetrical puzzles must be sufficiently wide for both lines'
+      if (this.pillar && this.symmetry.x && width % 4 !== 0) return 'X + Pillar symmetry must be an even number of rows, to keep both startpoints at the same parity'
+    }
+
+    return null
+  }
+
+
+  // Called on a solution. Computes a list of gaps to show as hints which *do not*
+  // break the path.
+  loadHints() {
+    this.hints = []
+    for (var x=0; x<this.width; x++) {
+      for (var y=0; y<this.height; y++) {
+        if (x%2 + y%2 === 1 && this.getLine(x, y) > window.LINE_NONE) {
+          this.hints.push({'x':x, 'y':y})
+        }
+      }
+    }
+  }
+
+  // Show a hint on the grid.
+  // If no hint is provided, will select the best one it can find,
+  // prioritizing breaking current lines on the grid.
+  // Returns the shown hint.
+  showHint(hint) {
+    if (hint != null) {
+      this.grid[hint.x][hint.y].gap = window.GAP_BREAK
+      return
+    }
+
+    var goodHints = []
+    var badHints = []
+
+    for (var hint of this.hints) {
+      if (this.getLine(hint.x, hint.y) > window.LINE_NONE) {
+        // Solution will be broken by this hint
+        goodHints.push(hint)
+      } else {
+        badHints.push(hint)
+      }
+    }
+    if (goodHints.length > 0) {
+      var hint = goodHints.splice(window.randInt(goodHints.length), 1)[0]
+    } else if (badHints.length > 0) {
+      var hint = badHints.splice(window.randInt(badHints.length), 1)[0]
+    } else {
+      return
+    }
+    this.grid[hint.x][hint.y].gap = window.GAP_BREAK
+    this.hints = badHints.concat(goodHints)
+    return hint
+  }
+
+  clearLines() {
+    for (var x=0; x<this.width; x++) {
+      for (var y=0; y<this.height; y++) {
+        this.updateCell2(x, y, 'line', 0)
+        this.updateCell2(x, y, 'dir', null)
+      }
+    }
+  }
+
+  _floodFill(x, y, region, col) {
+    var cell = col[y]
+    if (cell === MASKED_PROCESSED) return
+    if (cell !== MASKED_INB_NONCOUNT) {
+      region.push({'x':x, 'y':y})
+    }
+    col[y] = MASKED_PROCESSED
+
+    if (y < this.height - 1)        this._floodFill(x,        y + 1, region, col)
+    if (y > 0)                      this._floodFill(x,        y - 1, region, col)
+    if (x < this.width - 1)         this._floodFill(x + 1,        y, region, this.grid[x+1])
+    else if (this.pillar !== false) this._floodFill(0,            y, region, this.grid[0])
+    if (x > 0)                      this._floodFill(x - 1,        y, region, this.grid[x-1])
+    else if (this.pillar !== false) this._floodFill(this.width-1, y, region, this.grid[this.width-1])
+  }
+
+  // Re-uses the same grid, but only called on edges which border the outside
+  // Called first to mark cells that are connected to the outside, i.e. should not be part of any region.
+  _floodFillOutside(x, y, col) {
+    var cell = col[y]
+    if (cell === MASKED_PROCESSED) return
+    if (x%2 !== y%2 && cell !== MASKED_GAP2) return // Only flood-fill through gap-2
+    if (x%2 === 0 && y%2 === 0 && cell === MASKED_DOT) return // Don't flood-fill through dots
+    col[y] = MASKED_PROCESSED
+
+    if (x%2 === 0 && y%2 === 0) return // Don't flood fill through corners (what? Clarify.)
+
+    if (y < this.height - 1)        this._floodFillOutside(x,        y + 1, col)
+    if (y > 0)                      this._floodFillOutside(x,        y - 1, col)
+    if (x < this.width - 1)         this._floodFillOutside(x + 1,        y, this.grid[x+1])
+    else if (this.pillar !== false) this._floodFillOutside(0,            y, this.grid[0])
+    if (x > 0)                      this._floodFillOutside(x - 1,        y, this.grid[x-1])
+    else if (this.pillar !== false) this._floodFillOutside(this.width-1, y, this.grid[this.width-1])
+  }
+
+  // Returns the original grid (pre-masking). You will need to switch back once you are done flood filling.
+  switchToMaskedGrid() {
+    // Make a copy of the grid -- we will be overwriting it
+    var savedGrid = this.grid
+    this.grid = new Array(this.width)
+    // Override all elements with empty lines -- this means that flood fill is just
+    // looking for lines with line=0.
+    for (var x=0; x<this.width; x++) {
+      var savedRow = savedGrid[x]
+      var row = new Array(this.height)
+      var skip = 1
+      if (x%2 === 1) { // Cells are always part of the region
+        for (var y=1; y<this.height; y+=2) row[y] = MASKED_INB_COUNT
+        skip = 2 // Skip these cells during iteration
+      }
+      for (var y=0; y<this.height; y+=skip) {
+        var cell = savedRow[y]
+        if (cell.line > window.LINE_NONE) {
+          row[y] = MASKED_PROCESSED // Traced lines should not be a part of the region
+        } else if (cell.gap === window.GAP_FULL) {
+          row[y] = MASKED_GAP2
+        } else if (cell.dot > window.DOT_NONE) {
+          row[y] = MASKED_DOT
+        } else {
+          row[y] = MASKED_INB_COUNT
+        }
+      }
+      this.grid[x] = row
+    }
+
+    // Starting at a mid-segment startpoint
+    if (this.startPoint != null && this.startPoint.x%2 !== this.startPoint.y%2) {
+      if (this.settings.FAT_STARTPOINTS) {
+        // This segment is not in any region (acts as a barrier)
+        this.grid[this.startPoint.x][this.startPoint.y] = MASKED_OOB
+      } else {
+        // This segment is part of this region (acts as an empty cell)
+        this.grid[this.startPoint.x][this.startPoint.y] = MASKED_INB_NONCOUNT
+      }
+    }
+
+    // Ending at a mid-segment endpoint
+    if (this.endPoint != null && this.endPoint.x%2 !== this.endPoint.y%2) {
+      // This segment is part of this region (acts as an empty cell)
+      this.grid[this.endPoint.x][this.endPoint.y] = MASKED_INB_NONCOUNT
+    }
+
+    // Mark all outside cells as 'not in any region' (aka null)
+
+    // Top and bottom edges
+    for (var x=1; x<this.width; x+=2) {
+      this._floodFillOutside(x, 0, this.grid[x])
+      this._floodFillOutside(x, this.height - 1, this.grid[x])
+    }
+
+    // Left and right edges (only applies to non-pillars)
+    if (this.pillar === false) {
+      for (var y=1; y<this.height; y+=2) {
+        this._floodFillOutside(0, y, this.grid[0])
+        this._floodFillOutside(this.width - 1, y, this.grid[this.width-1])
+      }
+    }
+
+    return savedGrid
+  }
+
+  getRegions() {
+    var regions = []
+    var savedGrid = this.switchToMaskedGrid()
+
+    for (var x=0; x<this.width; x++) {
+      for (var y=0; y<this.height; y++) {
+        if (this.grid[x][y] == MASKED_PROCESSED) continue
+
+        // If this cell is empty (aka hasn't already been used by a region), then create a new one
+        // This will also mark all lines inside the new region as used.
+        var region = []
+        this._floodFill(x, y, region, this.grid[x])
+        regions.push(region)
+      }
+    }
+    this.grid = savedGrid
+    return regions
+  }
+
+  getRegion(x, y) {
+    x = this._mod(x)
+    if (!this._safeCell(x, y)) return
+
+    var savedGrid = this.switchToMaskedGrid()
+    if (this.grid[x][y] == MASKED_PROCESSED) {
+      this.grid = savedGrid
+      return null
+    }
+
+    // If the masked grid hasn't been used at this point, then create a new region.
+    // This will also mark all lines inside the new region as used.
+    var region = []
+    this._floodFill(x, y, region, this.grid[x])
+
+    this.grid = savedGrid
+    return region
+  }
+
+  logGrid() {
+    var output = ''
+    for (var y=0; y<this.height; y++) {
+      var row = []
+      for (var x=0; x<this.width; x++) {
+        var cell = this.getCell(x, y)
+        if (cell == null)                  row[x] = ' '
+        else if (cell.type === 'nonce')    row[x] = ' '
+        else if (cell.start === true)      row[x] = 'S'
+        else if (cell.end != null)         row[x] = 'E'
+        else if (cell.type === 'line') {
+          if (cell.gap > 0)                row[x] = ' '
+          if (cell.dot > 0)                row[x] = 'X'
+          if (cell.line === 0)             row[x] = '.'
+          if (cell.line === 1)             row[x] = '#'
+          if (cell.line === 2)             row[x] = '#'
+          if (cell.line === 3)             row[x] = 'o'
+        } else                             row[x] = '?'
+      }
+      output += row.join('') + '\n'
+    }
+    console.info(output)
+  }
+}
+
+// The grid contains 5 colors:
+// null: Out of bounds or already processed
+var MASKED_OOB = null
+var MASKED_PROCESSED = null
+// 0: In bounds, awaiting processing, but should not be part of the final region.
+var MASKED_INB_NONCOUNT = 0
+// 1: In bounds, awaiting processing
+var MASKED_INB_COUNT = 1
+// 2: Gap-2. After _floodFillOutside, this means "treat normally" (it will be null if oob)
+var MASKED_GAP2 = 2
+// 3: Dot (of any kind), otherwise identical to 1. Should not be flood-filled through (why the f do we need this)
+var MASKED_DOT = 3
+
+})
@@ -0,0 +1,346 @@
+namespace(function() {
+
+window.serializePuzzle = function(puzzle) {
+  var s = new Serializer('w')
+  var version = 0
+
+  s.writeInt(version)
+  s.writeByte(puzzle.width)
+  s.writeByte(puzzle.height)
+  s.writeString(puzzle.name)
+
+  var genericFlags = 0
+  if (puzzle.autoSolved) genericFlags |= GENERIC_FLAG_AUTOSOLVED
+  if (puzzle.symmetry) {
+    genericFlags |= GENERIC_FLAG_SYMMETRICAL
+    if (puzzle.symmetry.x) genericFlags |= GENERIC_FLAG_SYMMETRY_X
+    if (puzzle.symmetry.y) genericFlags |= GENERIC_FLAG_SYMMETRY_Y
+  }
+  if (puzzle.pillar) genericFlags |= GENERIC_FLAG_PILLAR
+  s.writeByte(genericFlags)
+  for (var x=0; x<puzzle.width; x++) {
+    for (var y=0; y<puzzle.height; y++) {
+      s.writeCell(puzzle.grid[x][y])
+    }
+  }
+
+  if (puzzle.path != null) {
+    var startPos = puzzle.path.pop()
+    if (puzzle.path.length > 0) {
+      s.writeInt(puzzle.path.length)
+      s.writeByte(startPos.x)
+      s.writeByte(startPos.y)
+      for (var dir of puzzle.path) s.writeByte(dir)
+    }
+  } else {
+    s.writeInt(0)
+  }
+
+  var settingsFlags = 0
+  if (puzzle.settings.NEGATIONS_CANCEL_NEGATIONS) settingsFlags |= SETTINGS_FLAG_NCN
+  if (puzzle.settings.SHAPELESS_ZERO_POLY)        settingsFlags |= SETTINGS_FLAG_SZP
+  if (puzzle.settings.PRECISE_POLYOMINOS)         settingsFlags |= SETTINGS_FLAG_PP
+  if (puzzle.settings.FLASH_FOR_ERRORS)           settingsFlags |= SETTINGS_FLAG_FFE
+  if (puzzle.settings.FAT_STARTPOINTS)            settingsFlags |= SETTINGS_FLAG_FS
+  if (puzzle.settings.CUSTOM_MECHANICS)           settingsFlags |= SETTINGS_FLAG_CM
+  s.writeByte(settingsFlags)
+
+  return s.str()
+}
+
+window.deserializePuzzle = function(data) {
+  // Data is JSON, so decode it with the old deserializer
+  if (data[0] == '{') return Puzzle.deserialize(data)
+
+  var s = new Serializer('r', data)
+  var version = s.readInt()
+  if (version > 0) throw Error('Cannot read data from unknown version: ' + version)
+
+  var width = s.readByte()
+  var height = s.readByte()
+  var puzzle = new Puzzle(Math.floor(width / 2), Math.floor(height / 2))
+  puzzle.name = s.readString()
+
+  var genericFlags = s.readByte()
+  puzzle.autoSolved = genericFlags & GENERIC_FLAG_AUTOSOLVED
+  if ((genericFlags & GENERIC_FLAG_SYMMETRICAL) != 0) {
+    puzzle.symmetry = {
+      'x': ((genericFlags & GENERIC_FLAG_SYMMETRY_X) != 0),
+      'y': ((genericFlags & GENERIC_FLAG_SYMMETRY_Y) != 0),
+    }
+  }
+  puzzle.pillar = (genericFlags & GENERIC_FLAG_PILLAR) != 0
+  for (var x=0; x<width; x++) {
+    for (var y=0; y<height; y++) {
+      puzzle.grid[x][y] = s.readCell()
+    }
+  }
+
+  var pathLength = s.readInt()
+  if (pathLength > 0) {
+    var path = [{
+      'x': s.readByte(),
+      'y': s.readByte(),
+    }]
+    for (var i=0; i<pathLength; i++) path.push(s.readByte())
+  }
+
+  var settingsFlags = s.readByte()
+  puzzle.settings = {
+    NEGATIONS_CANCEL_NEGATIONS: (settingsFlags & SETTINGS_FLAG_NCN) != 0,
+    SHAPELESS_ZERO_POLY:        (settingsFlags & SETTINGS_FLAG_SZP) != 0,
+    PRECISE_POLYOMINOS:         (settingsFlags & SETTINGS_FLAG_PP) != 0,
+    FLASH_FOR_ERRORS:           (settingsFlags & SETTINGS_FLAG_FFE) != 0,
+    FAT_STARTPOINTS:            (settingsFlags & SETTINGS_FLAG_FS) != 0,
+    CUSTOM_MECHANICS:           (settingsFlags & SETTINGS_FLAG_CM) != 0,
+  }
+
+  s.destroy()
+  return puzzle
+}
+
+class Serializer {
+  constructor(mode, data) {
+    this.mode = mode
+    if (mode == 'r') {
+      if (data == null) throw Error('No data provided to a read constructor')
+      if (data[0] != '_') throw Error('Cannot read data, improperly prefixed')
+      this.data = window.atob(data.slice(1))
+      this.index = 0
+    } else if (mode == 'w') {
+      this.data = []
+
+      var canvas = document.createElement('canvas')
+      canvas.height = 1
+      canvas.width = 1
+      this.colorConverter = canvas.getContext('2d')
+    } else {
+      throw Error('Unknown serializer mode: ' + mode)
+    }
+
+  }
+
+  destroy() {
+    if (this.mode == 'r' && this.index < this.data.length) {
+      throw Error('Read not done, ' + (this.data.length - this.index) + ' bytes remain')
+    }
+  }
+
+  str() {
+    if (this.mode != 'w') throw Error('Cannot get string from a serializer opened in mode: ' + this.mode)
+    return '_' + window.btoa(this.data)
+  }
+
+  _checkRead(numBytes = 1) {
+    if (this.mode != 'r') throw Error('Cannot read data from a serializer opened in mode: ' + this.mode)
+    if (this.data.length < numBytes) throw Error('Cannot read ' + numBytes + ' bytes from a stream with only '+ this.data.length + ' bytes')
+  }
+
+  readByte() {
+    this._checkRead()
+    return this.data.charCodeAt(this.index++)
+  }
+
+  writeByte(b) {
+    if (b < 0 || b > 0xFF) throw Error('Cannot write out-of-range byte ' + b)
+    this.data += String.fromCharCode(b)
+  }
+
+  readInt() {
+    var b1 = this.readByte() << 0
+    var b2 = this.readByte() << 8
+    var b3 = this.readByte() << 16
+    var b4 = this.readByte() << 24
+    return b1 | b2 | b3 | b4
+  }
+
+  writeInt(i) {
+    if (i < 0 || i > 0xFFFFFFFF) throw Error('Cannot write out-of-range int ' + i)
+    var b1 = (i & 0x000000FF) >> 0
+    var b2 = (i & 0x0000FF00) >> 8
+    var b3 = (i & 0x00FF0000) >> 16
+    var b4 = (i & 0xFF000000) >> 24
+    this.writeByte(b1)
+    this.writeByte(b2)
+    this.writeByte(b3)
+    this.writeByte(b4)
+  }
+
+  readLong() {
+    var i1 = this.readInt() << 32
+    var i2 = this.readInt()
+    return i1 | i2
+  }
+
+  writeLong(l) {
+    if (l < 0 || l > 0xFFFFFFFFFFFFFFFF) throw Error('Cannot write out-of-range long ' + l)
+    var i1 = l & 0xFFFFFFFF
+    var i2 = (l - i1) / 0x100000000
+    this.writeInt(i1)
+    this.writeInt(i2)
+  }
+
+  readString() {
+    var len = this.readInt()
+    this._checkRead(len)
+    var str = this.data.substr(this.index, len)
+    this.index += len
+    return str
+  }
+
+  writeString(s) {
+    if (s == null) {
+      this.writeInt(0)
+      return
+    }
+    this.writeInt(s.length)
+    this.data += s
+  }
+
+  readColor() {
+    var r = this.readByte().toString()
+    var g = this.readByte().toString()
+    var b = this.readByte().toString()
+    var a = this.readByte().toString()
+    return 'rgba(' + r + ', ' + g + ', ' + b + ', ' + a + ')'
+  }
+
+  writeColor(c) {
+    // Adapted from https://gist.github.com/njvack/02ad8efcb0d552b0230d
+    this.colorConverter.fillStyle = 'rgba(0, 0, 0, 0)' // Load a default in case we are passed garbage
+    this.colorConverter.clearRect(0, 0, 1, 1)
+    this.colorConverter.fillStyle = c
+    this.colorConverter.fillRect(0, 0, 1, 1)
+    var rgba = this.colorConverter.getImageData(0, 0, 1, 1).data
+    this.writeByte(rgba[0])
+    this.writeByte(rgba[1])
+    this.writeByte(rgba[2])
+    this.writeByte(rgba[3])
+  }
+
+  readCell() {
+    var cellType = this.readByte()
+    if (cellType === CELL_TYPE_NULL) return null
+
+    var cell = {}
+    cell.dir = null
+    cell.line = 0
+    if (cellType === CELL_TYPE_LINE) {
+      cell.type = 'line'
+      cell.line = this.readByte()
+      var dot = this.readByte()
+      if (dot != 0) cell.dot = dot
+      var gap = this.readByte()
+      if (gap != 0) cell.gap = gap
+    } else if (cellType === CELL_TYPE_SQUARE) {
+      cell.type = 'square'
+      cell.color = this.readColor()
+    } else if (cellType === CELL_TYPE_STAR) {
+      cell.type = 'star'
+      cell.color = this.readColor()
+    } else if (cellType === CELL_TYPE_NEGA) {
+      cell.type = 'nega'
+      cell.color = this.readColor()
+    } else if (cellType === CELL_TYPE_TRIANGLE) {
+      cell.type = 'triangle'
+      cell.color = this.readColor()
+      cell.count = this.readByte()
+    } else if (cellType === CELL_TYPE_POLY) {
+      cell.type = 'poly'
+      cell.color = this.readColor()
+      cell.polyshape = this.readLong()
+    } else if (cellType === CELL_TYPE_YLOP) {
+      cell.type = 'ylop'
+      cell.color = this.readColor()
+      cell.polyshape = this.readLong()
+    } else if (cellType == CELL_TYPE_NONCE) {
+      cell.type = 'nonce'
+    }
+
+    var startEnd = this.readByte()
+    if (startEnd & CELL_START)      cell.start = true
+    if (startEnd & CELL_END_LEFT)   cell.end = 'left'
+    if (startEnd & CELL_END_RIGHT)  cell.end = 'right'
+    if (startEnd & CELL_END_TOP)    cell.end = 'top'
+    if (startEnd & CELL_END_BOTTOM) cell.end = 'bottom'
+
+    return cell
+  }
+
+
+  writeCell(cell) {
+    if (cell == null) {
+      this.writeByte(CELL_TYPE_NULL)
+      return
+    }
+
+    // Write cell type, then cell data, then generic data.
+    // Note that cell type starts at 1, since 0 is the "null type".
+    if (cell.type == 'line') {
+      this.writeByte(CELL_TYPE_LINE)
+      this.writeByte(cell.line)
+      this.writeByte(cell.dot)
+      this.writeByte(cell.gap)
+    } else if (cell.type == 'square') {
+      this.writeByte(CELL_TYPE_SQUARE)
+      this.writeColor(cell.color)
+    } else if (cell.type == 'star') {
+      this.writeByte(CELL_TYPE_STAR)
+      this.writeColor(cell.color)
+    } else if (cell.type == 'nega') {
+      this.writeByte(CELL_TYPE_NEGA)
+      this.writeColor(cell.color)
+    } else if (cell.type == 'triangle') {
+      this.writeByte(CELL_TYPE_TRIANGLE)
+      this.writeColor(cell.color)
+      this.writeByte(cell.count)
+    } else if (cell.type == 'poly') {
+      this.writeByte(CELL_TYPE_POLY)
+      this.writeColor(cell.color)
+      this.writeLong(cell.polyshape)
+    } else if (cell.type == 'ylop') {
+      this.writeByte(CELL_TYPE_YLOP)
+      this.writeColor(cell.color)
+      this.writeLong(cell.polyshape)
+    }
+
+    var startEnd = 0
+    if (cell.start === true)  startEnd |= CELL_START
+    if (cell.end == 'left')   startEnd |= CELL_END_LEFT
+    if (cell.end == 'right')  startEnd |= CELL_END_RIGHT
+    if (cell.end == 'top')    startEnd |= CELL_END_TOP
+    if (cell.end == 'bottom') startEnd |= CELL_END_BOTTOM
+    this.writeByte(startEnd)
+  }
+}
+
+var CELL_TYPE_NULL     = 0
+var CELL_TYPE_LINE     = 1
+var CELL_TYPE_SQUARE   = 2
+var CELL_TYPE_STAR     = 3
+var CELL_TYPE_NEGA     = 4
+var CELL_TYPE_TRIANGLE = 5
+var CELL_TYPE_POLY     = 6
+var CELL_TYPE_YLOP     = 7
+var CELL_TYPE_NONCE    = 8
+
+var CELL_START         = 1
+var CELL_END_LEFT      = 2
+var CELL_END_RIGHT     = 4
+var CELL_END_TOP       = 8
+var CELL_END_BOTTOM    = 16
+
+var GENERIC_FLAG_AUTOSOLVED   = 1
+var GENERIC_FLAG_SYMMETRICAL  = 2
+var GENERIC_FLAG_SYMMETRY_X   = 4
+var GENERIC_FLAG_SYMMETRY_Y   = 8
+var GENERIC_FLAG_PILLAR       = 16
+
+var SETTINGS_FLAG_NCN         = 1
+var SETTINGS_FLAG_SZP         = 2
+var SETTINGS_FLAG_PP          = 4
+var SETTINGS_FLAG_FFE         = 8
+var SETTINGS_FLAG_FS          = 16
+var SETTINGS_FLAG_CM          = 32
+
+})
@@ -0,0 +1,531 @@
+namespace(function() {
+
+// @Volatile -- must match order of MOVE_* in trace2
+// Move these, dummy.
+var PATH_NONE   = 0
+var PATH_LEFT   = 1
+var PATH_RIGHT  = 2
+var PATH_TOP    = 3
+var PATH_BOTTOM = 4
+
+window.MAX_SOLUTIONS = 0
+var solutionPaths = []
+var asyncTimer = 0
+var task = null
+var puzzle = null
+var path = []
+var SOLVE_SYNC = false
+var SYNC_THRESHOLD = 9 // Depth at which we switch to a synchronous solver (for perf)
+var doPruning = false
+
+var percentages = []
+var NODE_DEPTH = 9
+var nodes = 0
+function countNodes(x, y, depth) {
+  // Check for collisions (outside, gap, self, other)
+  var cell = puzzle.getCell(x, y)
+  if (cell == null) return
+  if (cell.gap > window.GAP_NONE) return
+  if (cell.line !== window.LINE_NONE) return
+
+  if (puzzle.symmetry == null) {
+    puzzle.updateCell2(x, y, 'line', window.LINE_BLACK)
+  } else {
+    var sym = puzzle.getSymmetricalPos(x, y)
+    if (puzzle.matchesSymmetricalPos(x, y, sym.x, sym.y)) return // Would collide with our reflection
+
+    var symCell = puzzle.getCell(sym.x, sym.y)
+    if (symCell.gap > window.GAP_NONE) return
+
+    puzzle.updateCell2(x, y, 'line', window.LINE_BLUE)
+    puzzle.updateCell2(sym.x, sym.y, 'line', window.LINE_YELLOW)
+  }
+
+  if (depth < NODE_DEPTH) {
+    nodes++
+
+    if (y%2 === 0) {
+      countNodes(x - 1, y, depth + 1)
+      countNodes(x + 1, y, depth + 1)
+    }
+
+    if (x%2 === 0) {
+      countNodes(x, y - 1, depth + 1)
+      countNodes(x, y + 1, depth + 1)
+    }
+  }
+
+  tailRecurse(x, y)
+}
+
+// Generates a solution via DFS recursive backtracking
+window.solve = function(p, partialCallback, finalCallback) {
+  if (task != null) throw Error('Cannot start another solve() while one is already in progress')
+  var start = (new Date()).getTime()
+
+  puzzle = p
+  var startPoints = []
+  var numEndpoints = 0
+  puzzle.hasNegations = false
+  puzzle.hasPolyominos = false
+  for (var x=0; x<puzzle.width; x++) {
+    for (var y=0; y<puzzle.height; y++) {
+      var cell = puzzle.grid[x][y]
+      if (cell == null) continue
+      if (cell.start === true) {
+        startPoints.push({'x': x, 'y': y})
+      }
+      if (cell.end != null) numEndpoints++
+      if (cell.type == 'nega') puzzle.hasNegations = true
+      if (cell.type == 'poly' || cell.type == 'ylop') puzzle.hasPolyominos = true
+    }
+  }
+
+  // Puzzles which are small enough should be solved synchronously, since the cost of asynchronizing
+  // is greater than the cost of the puzzle.
+  SOLVE_SYNC = false
+  if (puzzle.symmetry != null) { // 5x5 is the max for symmetry puzzles
+    if (puzzle.width * puzzle.height <= 121) SOLVE_SYNC = true
+  } else if (puzzle.pillar === true) { // 4x5 is the max for non-symmetry, pillar puzzles
+    if (puzzle.width * puzzle.height <= 108) SOLVE_SYNC = true
+  } else { // 5x5 is the max for non-symmetry, non-pillar puzzles
+    if (puzzle.width * puzzle.height <= 121) SOLVE_SYNC = true
+  }
+  console.log('Puzzle is a', puzzle.width, 'by', puzzle.height, 'solving ' + (SOLVE_SYNC ? 'sync' : 'async'))
+
+  // We pre-traverse the grid (only considering obvious failure states like going out of bounds),
+  // and compute a total number of nodes that are reachable within some NODE_DEPTH steps.
+  // Then, during actual traversal, we can compare the number of nodes reached to the precomputed count
+  // to get a (fairly accurate) progress bar.
+  for (var pos of startPoints) {
+    countNodes(pos.x, pos.y, 0)
+  }
+  console.log('Pretraversal found', nodes, 'nodes')
+  percentages = []
+  for (var i=0; i<100; i++) {
+    percentages.push(Math.floor(i * nodes / 100))
+  }
+  nodes = 0
+
+  solutionPaths = []
+  // Some reasonable default data, which will avoid crashes during the solveLoop.
+  var earlyExitData = [false, {'isEdge': false}, {'isEdge': false}]
+  if (window.MAX_SOLUTIONS === 0) window.MAX_SOLUTIONS = 10000
+
+  // Large pruning optimization -- Attempt to early exit once we cut out a region.
+  // Inspired by https://github.com/Overv/TheWitnessSolver
+  // For non-pillar puzzles, every time we draw a line from one edge to another, we cut out two regions.
+  // We can detect this by asking if we've ever left an edge, and determining if we've just touched an edge.
+  // However, just touching the edge isn't sufficient, since we could still enter either region.
+  // As such, we wait one additional step, to see which half we have moved in to, then we evaluate
+  // whichever half you moved away from (since you can no longer re-enter it).
+  //
+  // Consider this pathway (tracing X-X-X-A-B-C).
+  // ....X....
+  // . . X . .
+  // ....X....
+  // . . A . .
+  // ...CB....
+  //
+  // Note that, once we have reached B, the puzzle is divided in half. However, we could go either
+  // left or right -- so we don't know which region is safe to validate.
+  // Once we reach C, however, the region to the right is closed off.
+  // As such, we can start a flood fill from the cell to the right of A, computed by A+(C-B).
+  //
+  // Unfortunately, this optimization doesn't work for pillars, since the two regions are still connected.
+  // Additionally, this optimization doesn't work when custom mechanics are active, as many custom mechanics
+  // depend on the path through the entire puzzle
+  doPruning = (puzzle.pillar === false && !puzzle.settings.CUSTOM_MECHANICS)
+
+  task = {
+    'code': function() {
+      var newTasks = []
+
+      for (var pos of startPoints) {
+        // ;(function(a){}(a))
+        // This syntax is used to forcibly copy arguments which are otherwise part of the loop.
+        // Note that we don't need to copy objects, just value types.
+        ;(function(pos) {
+          newTasks.push(function() {
+            path = [pos]
+            puzzle.startPoint = pos
+            return solveLoop(pos.x, pos.y, numEndpoints, earlyExitData)
+          })
+        }(pos))
+      }
+      return newTasks
+    }
+  }
+
+  taskLoop(partialCallback, function() {
+    var end = (new Date()).getTime()
+    console.log('Solved', puzzle, 'in', (end-start)/1000, 'seconds')
+    if (finalCallback) finalCallback(solutionPaths)
+  })
+  return solutionPaths
+}
+
+function taskLoop(partialCallback, finalCallback) {
+  if (task == null) {
+    finalCallback()
+    return
+  }
+
+  var newTasks = task.code()
+  task = task.nextTask
+  if (newTasks != null && newTasks.length > 0) {
+    // Tasks are pushed in order. To do DFS, we need to enqueue them in reverse order.
+    for (var i=newTasks.length - 1; i >= 0; i--) {
+      task = {
+        'code': newTasks[i],
+        'nextTask': task,
+      }
+    }
+  }
+
+  // Asynchronizing is expensive. As such, we don't want to do it too often.
+  // However, we would like 'cancel solving' to be responsive. So, we call setTimeout every so often.
+  var doAsync = false
+  if (!SOLVE_SYNC) {
+    doAsync = (asyncTimer++ % 100 === 0)
+    while (nodes >= percentages[0]) {
+      if (partialCallback) partialCallback(100 - percentages.length)
+      percentages.shift()
+      doAsync = true
+    }
+  }
+
+  if (doAsync) {
+    setTimeout(function() {
+      taskLoop(partialCallback, finalCallback)
+    }, 0)
+  } else {
+    taskLoop(partialCallback, finalCallback)
+  }
+}
+
+function tailRecurse(x, y) {
+  // Tail recursion: Back out of this cell
+  puzzle.updateCell2(x, y, 'line', window.LINE_NONE)
+  if (puzzle.symmetry != null) {
+    var sym = puzzle.getSymmetricalPos(x, y)
+    puzzle.updateCell2(sym.x, sym.y, 'line', window.LINE_NONE)
+  }
+}
+
+// @Performance: This is the most central loop in this code.
+// Any performance efforts should be focused here.
+// Note: Most mechanics are NP (or harder), so don't feel bad about solving them by brute force.
+// https://arxiv.org/pdf/1804.10193.pdf
+function solveLoop(x, y, numEndpoints, earlyExitData) {
+  // Stop trying to solve once we reach our goal
+  if (solutionPaths.length >= window.MAX_SOLUTIONS) return
+
+  // Check for collisions (outside, gap, self, other)
+  var cell = puzzle.getCell(x, y)
+  if (cell == null) return
+  if (cell.gap > window.GAP_NONE) return
+  if (cell.line !== window.LINE_NONE) return
+
+  if (puzzle.symmetry == null) {
+    puzzle.updateCell2(x, y, 'line', window.LINE_BLACK)
+  } else {
+    var sym = puzzle.getSymmetricalPos(x, y)
+    if (puzzle.matchesSymmetricalPos(x, y, sym.x, sym.y)) return // Would collide with our reflection
+
+    var symCell = puzzle.getCell(sym.x, sym.y)
+    if (symCell.gap > window.GAP_NONE) return
+
+    puzzle.updateCell2(x, y, 'line', window.LINE_BLUE)
+    puzzle.updateCell2(sym.x, sym.y, 'line', window.LINE_YELLOW)
+  }
+
+  if (path.length < NODE_DEPTH) nodes++
+
+  if (cell.end != null) {
+    path.push(PATH_NONE)
+    puzzle.endPoint = {'x': x, 'y': y}
+    var puzzleData = window.validate(puzzle, true)
+    if (puzzleData.valid()) solutionPaths.push(path.slice())
+    path.pop()
+
+    // If there are no further endpoints, tail recurse.
+    // Otherwise, keep going -- we might be able to reach another endpoint.
+    numEndpoints--
+    if (numEndpoints === 0) return tailRecurse(x, y)
+  }
+
+  var newEarlyExitData = null
+  if (doPruning) {
+    var isEdge = x <= 0 || y <= 0 || x >= puzzle.width - 1 || y >= puzzle.height - 1
+    newEarlyExitData = [
+      earlyExitData[0] || (!isEdge && earlyExitData[2].isEdge), // Have we ever left an edge?
+      earlyExitData[2],                                         // The position before our current one
+      {'x':x, 'y':y, 'isEdge':isEdge}                           // Our current position.
+    ]
+    if (earlyExitData[0] && !earlyExitData[1].isEdge && earlyExitData[2].isEdge && isEdge) {
+      // See the above comment for an explanation of this math.
+      var floodX = earlyExitData[2].x + (earlyExitData[1].x - x)
+      var floodY = earlyExitData[2].y + (earlyExitData[1].y - y)
+      var region = puzzle.getRegion(floodX, floodY)
+      if (region != null) {
+        var regionData = window.validateRegion(puzzle, region, true)
+        if (!regionData.valid()) return tailRecurse(x, y)
+
+        // Additionally, we might have left an endpoint in the enclosed region.
+        // If so, we should decrement the number of remaining endpoints (and possibly tail recurse).
+        for (var pos of region) {
+          var endCell = puzzle.grid[pos.x][pos.y]
+          if (endCell != null && endCell.end != null) numEndpoints--
+        }
+
+        if (numEndpoints === 0) return tailRecurse(x, y)
+      }
+    }
+  }
+
+  if (SOLVE_SYNC || path.length > SYNC_THRESHOLD) {
+    path.push(PATH_NONE)
+
+    // Recursion order (LRUD) is optimized for BL->TR and mid-start puzzles
+    if (y%2 === 0) {
+      path[path.length-1] = PATH_LEFT
+      solveLoop(x - 1, y, numEndpoints, newEarlyExitData)
+
+      path[path.length-1] = PATH_RIGHT
+      solveLoop(x + 1, y, numEndpoints, newEarlyExitData)
+    }
+
+    if (x%2 === 0) {
+      path[path.length-1] = PATH_TOP
+      solveLoop(x, y - 1, numEndpoints, newEarlyExitData)
+
+      path[path.length-1] = PATH_BOTTOM
+      solveLoop(x, y + 1, numEndpoints, newEarlyExitData)
+    }
+
+    path.pop()
+    tailRecurse(x, y)
+
+  } else {
+    // Push a dummy element on the end of the path, so that we can fill it correctly as we DFS.
+    // This element is popped when we tail recurse (which always happens *after* all of our DFS!)
+    path.push(PATH_NONE)
+
+    // Recursion order (LRUD) is optimized for BL->TR and mid-start puzzles
+    var newTasks = []
+    if (y%2 === 0) {
+      newTasks.push(function() {
+        path[path.length-1] = PATH_LEFT
+        return solveLoop(x - 1, y, numEndpoints, newEarlyExitData)
+      })
+      newTasks.push(function() {
+        path[path.length-1] = PATH_RIGHT
+        return solveLoop(x + 1, y, numEndpoints, newEarlyExitData)
+      })
+    }
+
+    if (x%2 === 0) {
+      newTasks.push(function() {
+        path[path.length-1] = PATH_TOP
+        return solveLoop(x, y - 1, numEndpoints, newEarlyExitData)
+      })
+      newTasks.push(function() {
+        path[path.length-1] = PATH_BOTTOM
+        return solveLoop(x, y + 1, numEndpoints, newEarlyExitData)
+      })
+    }
+
+    newTasks.push(function() {
+      path.pop()
+      tailRecurse(x, y)
+    })
+
+    return newTasks
+  }
+}
+
+window.cancelSolving = function() {
+  console.info('Cancelled solving')
+  window.MAX_SOLUTIONS = 0 // Causes all new solveLoop calls to exit immediately.
+  tasks = []
+}
+
+// Only modifies the puzzle object (does not do any graphics updates). Used by metapuzzle.js to determine subpuzzle polyshapes.
+window.drawPathNoUI = function(puzzle, path) {
+  puzzle.clearLines()
+
+  // Extract the start data from the first path element
+  var x = path[0].x
+  var y = path[0].y
+  var cell = puzzle.getCell(x, y)
+  if (cell == null || cell.start !== true) throw Error('Path does not begin with a startpoint: ' + JSON.stringify(cell))
+
+  for (var i=1; i<path.length; i++) {
+    var cell = puzzle.getCell(x, y)
+
+    var dx = 0
+    var dy = 0
+    if (path[i] === PATH_NONE) { // Reached an endpoint, move into it
+      console.debug('Reached endpoint')
+      if (i != path.length-1) throw Error('Path contains ' + (path.length - 1 - i) + ' trailing directions')
+      break
+    } else if (path[i] === PATH_LEFT) dx = -1
+    else if (path[i] === PATH_RIGHT)  dx = +1
+    else if (path[i] === PATH_TOP)    dy = -1
+    else if (path[i] === PATH_BOTTOM) dy = +1
+    else throw Error('Path element ' + (i-1) + ' was not a valid path direction: ' + path[i])
+
+    x += dx
+    y += dy
+    // Set the cell color
+    if (puzzle.symmetry == null) {
+      cell.line = window.LINE_BLACK
+    } else {
+      cell.line = window.LINE_BLUE
+      var sym = puzzle.getSymmetricalPos(x, y)
+      puzzle.updateCell2(sym.x, sym.y, 'line', window.LINE_YELLOW)
+    }
+  }
+
+  var cell = puzzle.getCell(x, y)
+  if (cell == null || cell.end == null) throw Error('Path does not end at an endpoint: ' + JSON.stringify(cell))
+}
+
+// Uses trace2 to draw the path on the grid, logs a graphical representation of the solution,
+// and also modifies the puzzle to contain the solution path.
+window.drawPath = function(puzzle, path, target='puzzle') {
+  // @Duplicated with trace2.clearGrid
+  var puzzleElem = document.getElementById(target)
+  window.deleteElementsByClassName(puzzleElem, 'cursor')
+  window.deleteElementsByClassName(puzzleElem, 'line-1')
+  window.deleteElementsByClassName(puzzleElem, 'line-2')
+  window.deleteElementsByClassName(puzzleElem, 'line-3')
+  puzzle.clearLines()
+  
+  if (path == null || path.length === 0) return // "drawing" an empty path is a shorthand for clearing the grid.
+
+  // Extract the start data from the first path element
+  var x = path[0].x
+  var y = path[0].y
+  var cell = puzzle.getCell(x, y)
+  if (cell == null || cell.start !== true) throw Error('Path does not begin with a startpoint: ' + JSON.stringify(cell))
+
+  var start = document.getElementById('start_' + target + '_' + x + '_' + y)
+  var symStart = document.getElementById('symStart_' + target + '_' + x + '_' + y)
+  window.onTraceStart(puzzle, {'x':x, 'y':y}, document.getElementById(target), start, symStart)
+
+  console.info('Drawing solution of length', path.length)
+  for (var i=1; i<path.length; i++) {
+    var cell = puzzle.getCell(x, y)
+
+    var dx = 0
+    var dy = 0
+    if (path[i] === PATH_NONE) { // Reached an endpoint, move into it
+      console.debug('Reached endpoint')
+      if (cell.end === 'left') {
+        window.onMove(-24, 0)
+      } else if (cell.end === 'right') {
+        window.onMove(24, 0)
+      } else if (cell.end === 'top') {
+        window.onMove(0, -24)
+      } else if (cell.end === 'bottom') {
+        window.onMove(0, 24)
+      }
+      if (i != path.length-1) throw Error('Path contains ' + (path.length - 1 - i) + ' trailing directions')
+      break
+    } else if (path[i] === PATH_LEFT) {
+      dx = -1
+      cell.dir = 'left'
+    } else if (path[i] === PATH_RIGHT) {
+      dx = +1
+      cell.dir = 'right'
+    } else if (path[i] === PATH_TOP) {
+      dy = -1
+      cell.dir = 'top'
+    } else if (path[i] === PATH_BOTTOM) {
+      dy = +1
+      cell.dir = 'down'
+    } else {
+      throw Error('Path element ' + (i-1) + ' was not a valid path direction: ' + path[i])
+    }
+
+    console.debug('Currently at', x, y, cell, 'moving', dx, dy)
+
+    x += dx
+    y += dy
+    // Unflag the cell, move into it, and reflag it
+    cell.line = window.LINE_NONE
+    window.onMove(41 * dx, 41 * dy)
+    if (puzzle.symmetry == null) {
+      cell.line = window.LINE_BLACK
+    } else {
+      cell.line = window.LINE_BLUE
+      var sym = puzzle.getSymmetricalPos(x, y)
+      puzzle.updateCell2(sym.x, sym.y, 'line', window.LINE_YELLOW)
+    }
+  }
+  var cell = puzzle.getCell(x, y)
+  if (cell == null || cell.end == null) throw Error('Path does not end at an endpoint: ' + JSON.stringify(cell))
+
+  var rows = '   |'
+  for (var x=0; x<puzzle.width; x++) {
+    rows += ('' + x).padEnd(5, ' ') + '|'
+  }
+  console.log(rows)
+  for (var y=0; y<puzzle.height; y++) {
+    var output = ('' + y).padEnd(3, ' ') + '|'
+    for (var x=0; x<puzzle.width; x++) {
+      var cell = puzzle.grid[x][y]
+      var dir = (cell != null && cell.dir != null ? cell.dir : '')
+      output += dir.padEnd(5, ' ') + '|'
+    }
+    console.log(output)
+  }
+}
+
+window.getSolutionIndex = function(pathList, solution) {
+  for (var i=0; i<pathList.length; i++) {
+    var path = pathList[i]
+    var x = path[0].x
+    var y = path[0].y
+    if (solution.grid[path[0].x][path[0].y].line === 0) continue
+
+    var match = true
+    for (var j=1; j<path.length; j++) {
+      var cell = solution.grid[x][y]
+      if (path[j] === PATH_NONE && cell.end != null) {
+        match = false
+        break
+      } else if (path[j] === PATH_LEFT) {
+        if (cell.dir != 'left') {
+          match = false
+          break
+        }
+        x--
+      } else if (path[j] === PATH_RIGHT) {
+        if (cell.dir != 'right') {
+          match = false
+          break
+        }
+        x++
+      } else if (path[j] === PATH_TOP) {
+        if (cell.dir != 'top') {
+          match = false
+          break
+        }
+        y--
+      } else if (path[j] === PATH_BOTTOM) {
+        if (cell.dir != 'bottom') {
+          match = false
+          break
+        }
+        y++
+      }
+    }
+    if (match) return i
+  }
+  return -1
+}
+
+})
@@ -0,0 +1,422 @@
+namespace(function() {
+
+window.createElement = function(type) {
+  return document.createElementNS('http://www.w3.org/2000/svg', type)
+}
+
+window.drawSymbol = function(params, customMechanics) {
+  var svg = createElement('svg')
+  svg.setAttribute('viewBox', '0 0 ' + params.width + ' ' + params.height)
+  if (!params.x) params.x = 0
+  if (!params.y) params.y = 0
+  drawSymbolWithSvg(svg, params, customMechanics)
+  return svg
+}
+
+window.drawSymbolWithSvg = function(svg, params, customMechanics) {
+  if (params.type == 'square')        square(svg, params)
+  else if (params.type == 'dot')      dot(svg, params)
+  else if (params.type == 'gap')      gap(svg, params)
+  else if (params.type == 'star')     star(svg, params)
+  else if (params.type == 'poly')     poly(svg, params)
+  else if (params.type == 'ylop')     ylop(svg, params)
+  else if (params.type == 'nega')     nega(svg, params)
+  else if (params.type == 'nonce')    { /* Do nothing */ }
+  else if (params.type == 'triangle') triangle(svg, params)
+  else if (params.type == 'crayon')   crayon(svg, params)
+  else if (params.type == 'start')    start(svg, params)
+  else if (params.type == 'end')      end(svg, params)
+  else if (params.type == 'drag')     drag(svg, params)
+  else if (params.type == 'plus')     plus(svg, params)
+  else if (params.type == 'minus')    minus(svg, params)
+  else if (params.type == 'bridge' && customMechanics) bridge(svg, params)
+  else if (params.type == 'arrow'  && customMechanics) arrow(svg, params)
+  else if (params.type == 'sizer'  && customMechanics) sizer(svg, params)
+  else {console.error('Cannot draw unknown SVG type: ' + params.type)}
+}
+
+function square(svg, params) {
+  var rect = createElement('rect')
+  svg.appendChild(rect)
+  rect.setAttribute('width', 28)
+  rect.setAttribute('height', 28)
+  rect.setAttribute('x', params.width/2-14 + params.x)
+  rect.setAttribute('y', params.height/2-14 + params.y)
+  rect.setAttribute('rx', 7)
+  rect.setAttribute('ry', 7)
+  rect.setAttribute('fill', params.color)
+  rect.setAttribute('class', params.class)
+}
+
+function star(svg, params) {
+  var poly = createElement('polygon')
+  svg.appendChild(poly)
+  var points = [
+    '-10.5 -10.5', // Top left
+    '-9.5 -4',
+    '-15 0',
+    '-9.5 4',
+    '-10.5 10.5', // Bottom left
+    '-4 9.5',
+    '0 15',
+    '4 9.5',
+    '10.5 10.5', // Bottom right
+    '9.5 4',
+    '15 0',
+    '9.5 -4',
+    '10.5 -10.5', // Top right
+    '4, -9.5',
+    '0 -15',
+    '-4 -9.5',
+  ]
+  poly.setAttribute('transform', 'translate(' + (params.width/2 + params.x) + ', ' + (params.height/2 + params.y) + ')')
+  poly.setAttribute('points', points.join(', '))
+  poly.setAttribute('fill', params.color)
+  poly.setAttribute('class', params.class)
+}
+
+function poly(svg, params) {
+  if (params.polyshape === 0) return
+  var size = 10 // Side length of individual squares in the polyomino
+  var space = 4 // Gap between squares in the polyomino
+  var polyomino = window.polyominoFromPolyshape(params.polyshape)
+
+  var bounds = {'xmin':0, 'xmax':0, 'ymin':0, 'ymax':0}
+  for (var i=0; i<polyomino.length; i++) {
+    var pos = polyomino[i]
+    bounds.xmin = Math.min(bounds.xmin, pos.x)
+    bounds.xmax = Math.max(bounds.xmax, pos.x)
+    bounds.ymin = Math.min(bounds.ymin, pos.y)
+    bounds.ymax = Math.max(bounds.ymax, pos.y)
+  }
+  var offset = (size+space)/2 // Offset between elements to create the gap
+  var centerX = (params.width - size - offset * (bounds.xmax + bounds.xmin)) / 2 + params.x
+  var centerY = (params.height - size - offset * (bounds.ymax + bounds.ymin)) / 2 + params.y
+
+  for (var i=0; i<polyomino.length; i++) {
+    var pos = polyomino[i]
+    if (pos.x%2 !== 0 || pos.y%2 !== 0) continue
+    var rect = createElement('rect')
+    rect.style.pointerEvents = 'none'
+    var transform = 'translate(' + (centerX + pos.x*offset) + ', ' + (centerY + pos.y*offset) + ')'
+    if (window.isRotated(params.polyshape)) {
+      // -30 degree rotation around the midpoint of the square
+      transform = 'rotate(-30, ' + (params.width/2 + params.x) + ', ' + (params.height/2 + params.y) + ') ' + transform
+    }
+    rect.setAttribute('transform', transform)
+    rect.setAttribute('height', size)
+    rect.setAttribute('width', size)
+    rect.setAttribute('fill', params.color)
+    rect.setAttribute('class', params.class)
+    svg.appendChild(rect)
+  }
+}
+
+function ylop(svg, params) {
+  if (params.polyshape === 0) return
+  var size = 12 // Side length of individual squares in the polyomino
+  var space = 2 // Gap between squares in the polyomino
+  var polyomino = window.polyominoFromPolyshape(params.polyshape)
+
+  var bounds = {'xmin':0, 'xmax':0, 'ymin':0, 'ymax':0}
+  for (var i=0; i<polyomino.length; i++) {
+    var pos = polyomino[i]
+    bounds.xmin = Math.min(bounds.xmin, pos.x)
+    bounds.xmax = Math.max(bounds.xmax, pos.x)
+    bounds.ymin = Math.min(bounds.ymin, pos.y)
+    bounds.ymax = Math.max(bounds.ymax, pos.y)
+  }
+  var offset = (size+space)/2 // Offset between elements to create the gap
+  var centerX = (params.width - size - offset * (bounds.xmax + bounds.xmin)) / 2 + params.x
+  var centerY = (params.height - size - offset * (bounds.ymax + bounds.ymin)) / 2 + params.y
+
+  for (var i=0; i<polyomino.length; i++) {
+    var pos = polyomino[i]
+    if (pos.x%2 !== 0 || pos.y%2 !== 0) continue
+    var poly = createElement('polygon')
+    poly.style.pointerEvents = 'none'
+    var points = [
+      '0 0', '12 0', '12 12', '0 12', '0 3',
+      '3 3', '3 9', '9 9', '9 3', '0 3',
+    ]
+    poly.setAttribute('points', points.join(', '))
+    var transform = 'translate(' + (centerX + pos.x*offset) + ', ' + (centerY + pos.y*offset) + ')'
+    if (window.isRotated(params.polyshape)) {
+      // -30 degree rotation around the midpoint of the square
+      transform = 'rotate(-30, ' + (params.width/2 + params.x) + ', ' + (params.height/2 + params.y) + ') ' + transform
+    }
+    poly.setAttribute('transform', transform)
+    poly.setAttribute('fill', params.color)
+    poly.setAttribute('class', params.class)
+    svg.appendChild(poly)
+  }
+}
+
+function nega(svg, params) {
+  var poly = createElement('polygon')
+  svg.appendChild(poly)
+  var points = [
+    '2.9 -2',
+    '2.9 -10.4',
+    '-2.9 -10.4',
+    '-2.9 -2',
+    '-10.2 2.2',
+    '-7.3 7.2',
+    '0 3',
+    '7.3 7.2',
+    '10.2 2.2',
+  ]
+  poly.setAttribute('transform', 'translate(' + (params.width/2 + params.x) + ', ' + (params.height/2 + params.y) + ')')
+  poly.setAttribute('points', points.join(', '))
+  poly.setAttribute('fill', params.color)
+  poly.setAttribute('class', params.class)
+}
+
+var triangleDistributions = [
+  [],
+  [1],
+  [2],
+  [3],
+  [2, 2],
+  [2, 3],
+  [3, 3],
+  [2, 3, 2],
+  [3, 2, 3],
+  [3, 3, 3]
+]
+
+function triangle(svg, params) {
+  var distribution = triangleDistributions[params.count]
+  var high = distribution.length
+  for (var y=0; y<high; y++) {
+    var wide = distribution[y]
+    for (var x=0; x<wide; x++) {
+      var poly = createElement('polygon')
+      svg.appendChild(poly)
+      var Xcoord = params.x + params.width/2 + 11*(2*x - wide + 1)
+      var Ycoord = params.y + params.height/2 + 10*(2*y - high + 1)
+      poly.setAttribute('transform', 'translate(' + Xcoord + ', ' + Ycoord + ')')
+      poly.setAttribute('points', '0 -8, -8 6, 8 6')
+      poly.setAttribute('fill', params.color)
+      poly.setAttribute('class', params.class)
+    }
+  }
+}
+
+function crayon(svg, params) {
+  var height = params.height
+
+  var poly = createElement('polygon')
+  svg.appendChild(poly)
+  var points = [
+    '0 ' + (height/2),
+    (height/2) + ' 0',
+    (height/2) + ' ' + height,
+  ]
+  poly.setAttribute('points', points.join(', '))
+  poly.setAttribute('fill', params.color)
+  var txt = createElement('text')
+  svg.appendChild(txt)
+  txt.setAttribute('fill', window.TEXT_COLOR)
+  txt.setAttribute('transform', 'translate(' + (height/2 + 10) + ', ' + (height/2 + 6) + ')')
+  txt.textContent = params.text
+}
+
+function start(svg, params) {
+  var circ = createElement('circle')
+  svg.appendChild(circ)
+  circ.setAttribute('r', 24)
+  circ.setAttribute('fill', window.FOREGROUND)
+  circ.setAttribute('cx', params.height/2 + params.x)
+  circ.setAttribute('cy', params.width/2 + params.y)
+}
+
+function end(svg, params) {
+  var rect = createElement('rect')
+  svg.appendChild(rect)
+  rect.setAttribute('width', 24)
+  rect.setAttribute('height', 24)
+  rect.setAttribute('fill', window.FOREGROUND)
+  rect.setAttribute('x', params.height/2 - 12 + params.x)
+  rect.setAttribute('y', params.width/2 - 12 + params.y)
+
+  var circ = createElement('circle')
+  svg.appendChild(circ)
+  circ.setAttribute('r', 12)
+  circ.setAttribute('fill', window.FOREGROUND)
+  circ.setAttribute('cx', params.height/2 + params.x)
+  circ.setAttribute('cy', params.width/2 + params.y)
+
+  if (params.dir === 'left') {
+    rect.setAttribute('x', parseInt(rect.getAttribute('x'), 10) - 12)
+    circ.setAttribute('cx', parseInt(circ.getAttribute('cx'), 10) - 24)
+  } else if (params.dir === 'right') {
+    rect.setAttribute('x', parseInt(rect.getAttribute('x'), 10) + 12)
+    circ.setAttribute('cx', parseInt(circ.getAttribute('cx'), 10) + 24)
+  } else if (params.dir === 'top') {
+    rect.setAttribute('y', parseInt(rect.getAttribute('y'), 10) - 12)
+    circ.setAttribute('cy', parseInt(circ.getAttribute('cy'), 10) - 24)
+  } else if (params.dir === 'bottom') {
+    rect.setAttribute('y', parseInt(rect.getAttribute('y'), 10) + 12)
+    circ.setAttribute('cy', parseInt(circ.getAttribute('cy'), 10) + 24)
+  } else {
+    console.error('Endpoint direction not defined!', JSON.stringify(params))
+  }
+}
+
+function dot(svg, params) {
+  var hex = createElement('polygon')
+  svg.appendChild(hex)
+  hex.setAttribute('points', '5.2 9, 10.4 0, 5.2 -9, -5.2 -9, -10.4 0, -5.2 9')
+  hex.setAttribute('transform', 'translate(' + (params.width/2 + params.x) + ', ' + (params.height/2 + params.y) + ')')
+  hex.setAttribute('fill', params.color)
+  hex.setAttribute('class', params.class)
+  hex.setAttribute('stroke', params.stroke)
+  hex.setAttribute('stroke-width', params.strokeWidth)
+  hex.setAttribute('style', 'pointer-events:none;')
+}
+
+function gap(svg, params) {
+  if (!params.rot) params.rot = 0
+  var centerX = params.height/2 + params.x
+  var centerY = params.width/2 + params.y
+  var rotate = function(degrees) {return 'rotate(' + degrees + ', ' + centerX + ', ' + centerY + ')'}
+
+  var rect = createElement('rect')
+  svg.appendChild(rect)
+  rect.setAttribute('width', 32)
+  rect.setAttribute('height', 24)
+  rect.setAttribute('fill', window.FOREGROUND)
+  rect.setAttribute('transform', rotate(90 * params.rot))
+  rect.setAttribute('x', centerX - 40)
+  rect.setAttribute('y', centerY - 12)
+  rect.setAttribute('shape-rendering', 'crispedges')
+
+  var rect = createElement('rect')
+  svg.appendChild(rect)
+  rect.setAttribute('width', 32)
+  rect.setAttribute('height', 24)
+  rect.setAttribute('fill', window.FOREGROUND)
+  rect.setAttribute('transform', rotate(90 * params.rot))
+  rect.setAttribute('x', centerX + 9)
+  rect.setAttribute('y', centerY - 12)
+  rect.setAttribute('shape-rendering', 'crispedges')
+}
+
+function drag(svg, params) {
+  if (!params.rot) params.rot = 0
+
+  for (var i=0; i<6; i++) {
+    for (var j=0; j<2; j++) {
+      var rect = createElement('rect')
+      svg.appendChild(rect)
+      rect.setAttribute('width', 2)
+      rect.setAttribute('height', 2)
+      if (params.rot === 0) {
+        rect.setAttribute('x', i*4)
+        rect.setAttribute('y', j*4)
+      } else {
+        rect.setAttribute('y', i*4)
+        rect.setAttribute('x', j*4)
+      }
+      rect.setAttribute('fill', window.PAGE_BACKGROUND)
+    }
+  }
+}
+
+function plus(svg, params) {
+  var verti = createElement('rect')
+  svg.appendChild(verti)
+  verti.setAttribute('x', params.width/2 - 1)
+  verti.setAttribute('y', 3)
+  verti.setAttribute('width', 2)
+  verti.setAttribute('height', params.height - 6)
+  verti.setAttribute('fill', window.TEXT_COLOR)
+  minus(svg, params)
+}
+
+function minus(svg, params) {
+  var horiz = createElement('rect')
+  svg.appendChild(horiz)
+  horiz.setAttribute('x', 3)
+  horiz.setAttribute('y', params.height/2 - 1)
+  horiz.setAttribute('width', params.width - 6)
+  horiz.setAttribute('height', 2)
+  horiz.setAttribute('fill', window.TEXT_COLOR)
+}
+
+function bridge(svg, params) {
+  var poly = createElement('polygon')
+  svg.appendChild(poly)
+  var points = [
+    '-10.58 14.56',
+    '-17.12 -5.56',
+    '0 -18',
+    '17.12 -5.56',
+    '10.58 14.56',
+    '5.29 7.28',
+    '8.56 -2.78',
+    '0 -9',
+    '-8.56 -2.78',
+    '-5.29 7.28',
+  ]
+  poly.setAttribute('transform', 'translate(' + (params.width/2 + params.x) + ', ' + (params.height/2 + params.y) + ')')
+  poly.setAttribute('points', points.join(', '))
+  poly.setAttribute('fill', params.color)
+  poly.setAttribute('class', params.class)
+}
+
+function arrow(svg, params) {
+  if (!params.rot) params.rot = 0
+
+  var centerX = params.height/2 + params.x
+  var centerY = params.width/2 + params.y
+  var rotate = function(degrees) {return 'rotate(' + degrees + ', ' + centerX + ', ' + centerY + ')'}
+
+  var rect = createElement('rect')
+  svg.appendChild(rect)
+  rect.setAttribute('width', 8)
+  rect.setAttribute('height', 46)
+  rect.setAttribute('fill', params.color)
+  rect.setAttribute('class', params.class)
+  rect.setAttribute('transform', rotate(45 * params.rot))
+  rect.setAttribute('x', centerX - 4)
+  rect.setAttribute('y', centerY - 22)
+
+  for (var i=0; i<params.count; i++) {
+    var arrowhead = createElement('polygon')
+    svg.appendChild(arrowhead)
+    var points = [
+      '-24 -15',
+      '-21.4 -8.6',
+      '0 -19',
+      '21.4 -8.6',
+      '24 -15',
+      '0 -27',
+    ]
+    var transform = rotate(45 * params.rot)
+    transform += ' translate(' + (params.width/2 + params.x) + ', ' + (params.height/2 + params.y + i*12) + ')'
+    arrowhead.setAttribute('transform', transform)
+    arrowhead.setAttribute('points', points.join(', '))
+    arrowhead.setAttribute('fill', params.color)
+    arrowhead.setAttribute('class', params.class)
+  }
+}
+
+function sizer(svg, params) {
+  var path = createElement('path')
+  svg.appendChild(path)
+  path.setAttribute('d',
+    'M -24 0 ' +
+    'a 24 24 0 0 0  24 -24 ' +
+    'a 24 24 0 0 0  24  24 ' +
+    'a 24 24 0 0 0 -24  24 ' +
+    'a 24 24 0 0 0 -24 -24 ' +
+    'z'
+  )
+  path.setAttribute('fill', params.color)
+  path.setAttribute('class', params.class)
+  path.setAttribute('transform', 'translate(' + (params.width/2 + params.x) + ', ' + (params.height/2 + params.y) + ')')
+}
+
+})
@@ -0,0 +1,988 @@
+namespace(function() {
+
+var BBOX_DEBUG = false
+
+function clamp(value, min, max) {
+  return value < min ? min : value > max ? max : value
+}
+
+class BoundingBox {
+  constructor(x1, x2, y1, y2, sym=false) {
+    this.raw = {'x1':x1, 'x2':x2, 'y1':y1, 'y2':y2}
+    this.sym = sym
+    if (BBOX_DEBUG === true) {
+      this.debug = createElement('rect')
+      data.svg.appendChild(this.debug)
+      this.debug.setAttribute('opacity', 0.5)
+      this.debug.setAttribute('style', 'pointer-events: none;')
+      if (data.puzzle.symmetry == null) {
+        this.debug.setAttribute('fill', 'white')
+      } else {
+        if (this.sym !== true) {
+          this.debug.setAttribute('fill', 'blue')
+        } else {
+          this.debug.setAttribute('fill', 'orange')
+        }
+      }
+    }
+    this._update()
+  }
+
+  shift(dir, pixels) {
+    if (dir === 'left') {
+      this.raw.x2 = this.raw.x1
+      this.raw.x1 -= pixels
+    } else if (dir === 'right') {
+      this.raw.x1 = this.raw.x2
+      this.raw.x2 += pixels
+    } else if (dir === 'top') {
+      this.raw.y2 = this.raw.y1
+      this.raw.y1 -= pixels
+    } else if (dir === 'bottom') {
+      this.raw.y1 = this.raw.y2
+      this.raw.y2 += pixels
+    }
+    this._update()
+  }
+
+  inMain(x, y) {
+    var inMainBox =
+      (this.x1 < x && x < this.x2) &&
+      (this.y1 < y && y < this.y2)
+    var inRawBox =
+      (this.raw.x1 < x && x < this.raw.x2) &&
+      (this.raw.y1 < y && y < this.raw.y2)
+
+    return inMainBox && !inRawBox
+  }
+
+  _update() {
+    this.x1 = this.raw.x1
+    this.x2 = this.raw.x2
+    this.y1 = this.raw.y1
+    this.y2 = this.raw.y2
+
+    // Check for endpoint adjustment
+    if (this.sym !== true) {
+      var cell = data.puzzle.getCell(data.pos.x, data.pos.y)
+    } else {
+      var cell = data.puzzle.getSymmetricalCell(data.sym.x, data.sym.y)
+    }
+    if (cell.end === 'left') {
+      this.x1 -= 24
+    } else if (cell.end === 'right') {
+      this.x2 += 24
+    } else if (cell.end === 'top') {
+      this.y1 -= 24
+    } else if (cell.end === 'bottom') {
+      this.y2 += 24
+    }
+
+    this.middle = { // Note: Middle of the raw object
+      'x':(this.raw.x1 + this.raw.x2)/2,
+      'y':(this.raw.y1 + this.raw.y2)/2
+    }
+
+    if (this.debug != null) {
+      this.debug.setAttribute('x', this.x1)
+      this.debug.setAttribute('y', this.y1)
+      this.debug.setAttribute('width', this.x2 - this.x1)
+      this.debug.setAttribute('height', this.y2 - this.y1)
+    }
+  }
+}
+
+class PathSegment {
+  constructor(dir) {
+    this.poly1 = createElement('polygon')
+    this.circ = createElement('circle')
+    this.poly2 = createElement('polygon')
+    this.pillarCirc = createElement('circle')
+    this.dir = dir
+    data.svg.insertBefore(this.circ, data.cursor)
+    data.svg.insertBefore(this.poly2, data.cursor)
+    data.svg.insertBefore(this.pillarCirc, data.cursor)
+    this.circ.setAttribute('cx', data.bbox.middle.x)
+    this.circ.setAttribute('cy', data.bbox.middle.y)
+
+    if (data.puzzle.pillar === true) {
+      // cx/cy are updated in redraw(), since pillarCirc tracks the cursor
+      this.pillarCirc.setAttribute('cy', data.bbox.middle.y)
+      this.pillarCirc.setAttribute('r', 12)
+      if (data.pos.x === 0 && this.dir === MOVE_RIGHT) {
+        this.pillarCirc.setAttribute('cx', data.bbox.x1)
+        this.pillarCirc.setAttribute('static', true)
+      } else if (data.pos.x === data.puzzle.width - 1 && this.dir === MOVE_LEFT) {
+        this.pillarCirc.setAttribute('cx', data.bbox.x2)
+        this.pillarCirc.setAttribute('static', true)
+      } else {
+        this.pillarCirc.setAttribute('cx', data.bbox.middle.x)
+      }
+    }
+
+    if (data.puzzle.symmetry == null) {
+      this.poly1.setAttribute('class', 'line-1 ' + data.svg.id)
+      this.circ.setAttribute('class', 'line-1 ' + data.svg.id)
+      this.poly2.setAttribute('class', 'line-1 ' + data.svg.id)
+      this.pillarCirc.setAttribute('class', 'line-1 ' + data.svg.id)
+    } else {
+      this.poly1.setAttribute('class', 'line-2 ' + data.svg.id)
+      this.circ.setAttribute('class', 'line-2 ' + data.svg.id)
+      this.poly2.setAttribute('class', 'line-2 ' + data.svg.id)
+      this.pillarCirc.setAttribute('class', 'line-2 ' + data.svg.id)
+
+      this.symPoly1 = createElement('polygon')
+      this.symCirc = createElement('circle')
+      this.symPoly2 = createElement('polygon')
+      this.symPillarCirc = createElement('circle')
+      data.svg.insertBefore(this.symCirc, data.cursor)
+      data.svg.insertBefore(this.symPoly2, data.cursor)
+      data.svg.insertBefore(this.symPillarCirc, data.cursor)
+      this.symPoly1.setAttribute('class', 'line-3 ' + data.svg.id)
+      this.symCirc.setAttribute('class', 'line-3 ' + data.svg.id)
+      this.symPoly2.setAttribute('class', 'line-3 ' + data.svg.id)
+      this.symPillarCirc.setAttribute('class', 'line-3 ' + data.svg.id)
+
+      this.symCirc.setAttribute('cx', data.symbbox.middle.x)
+      this.symCirc.setAttribute('cy', data.symbbox.middle.y)
+
+      if (data.puzzle.pillar === true) {
+        // cx/cy are updated in redraw(), since symPillarCirc tracks the cursor
+        this.symPillarCirc.setAttribute('cy', data.symbbox.middle.y)
+        this.symPillarCirc.setAttribute('r', 12)
+        var symmetricalDir = getSymmetricalDir(data.puzzle, this.dir)
+        if (data.sym.x === 0 && symmetricalDir === MOVE_RIGHT) {
+          this.symPillarCirc.setAttribute('cx', data.symbbox.x1)
+          this.symPillarCirc.setAttribute('static', true)
+        } else if (data.sym.x === data.puzzle.width - 1 && symmetricalDir === MOVE_LEFT) {
+          this.symPillarCirc.setAttribute('cx', data.symbbox.x2)
+          this.symPillarCirc.setAttribute('static', true)
+        } else {
+          this.symPillarCirc.setAttribute('cx', data.symbbox.middle.x)
+        }
+      }
+    }
+
+    if (this.dir === MOVE_NONE) { // Start point
+      this.circ.setAttribute('r', 24)
+      this.circ.setAttribute('class', this.circ.getAttribute('class') + ' start')
+      if (data.puzzle.symmetry != null) {
+        this.symCirc.setAttribute('r', 24)
+        this.symCirc.setAttribute('class', this.symCirc.getAttribute('class') + ' start')
+      }
+    } else {
+      // Only insert poly1 in non-startpoints
+      data.svg.insertBefore(this.poly1, data.cursor)
+      this.circ.setAttribute('r', 12)
+      if (data.puzzle.symmetry != null) {
+        data.svg.insertBefore(this.symPoly1, data.cursor)
+        this.symCirc.setAttribute('r', 12)
+      }
+    }
+  }
+
+  destroy() {
+    data.svg.removeChild(this.poly1)
+    data.svg.removeChild(this.circ)
+    data.svg.removeChild(this.poly2)
+    data.svg.removeChild(this.pillarCirc)
+    if (data.puzzle.symmetry != null) {
+      data.svg.removeChild(this.symPoly1)
+      data.svg.removeChild(this.symCirc)
+      data.svg.removeChild(this.symPoly2)
+      data.svg.removeChild(this.symPillarCirc)
+    }
+  }
+
+  redraw() { // Uses raw bbox because of endpoints
+    // Move the cursor and related objects
+    var x = clamp(data.x, data.bbox.x1, data.bbox.x2)
+    var y = clamp(data.y, data.bbox.y1, data.bbox.y2)
+    data.cursor.setAttribute('cx', x)
+    data.cursor.setAttribute('cy', y)
+    if (data.puzzle.symmetry != null) {
+      data.symcursor.setAttribute('cx', this._reflX(x))
+      data.symcursor.setAttribute('cy', this._reflY(y))
+    }
+    if (data.puzzle.pillar === true) {
+      if (this.pillarCirc.getAttribute('static') == null) {
+        this.pillarCirc.setAttribute('cx', x)
+        this.pillarCirc.setAttribute('cy', y)
+      }
+      if (data.puzzle.symmetry != null) {
+        if (this.symPillarCirc.getAttribute('static') == null) {
+          this.symPillarCirc.setAttribute('cx', this._reflX(x))
+          this.symPillarCirc.setAttribute('cy', this._reflY(y))
+        }
+      }
+    }
+
+    // Draw the first-half box
+    var points1 = JSON.parse(JSON.stringify(data.bbox.raw))
+    if (this.dir === MOVE_LEFT) {
+      points1.x1 = clamp(data.x, data.bbox.middle.x, data.bbox.x2)
+    } else if (this.dir === MOVE_RIGHT) {
+      points1.x2 = clamp(data.x, data.bbox.x1, data.bbox.middle.x)
+    } else if (this.dir === MOVE_TOP) {
+      points1.y1 = clamp(data.y, data.bbox.middle.y, data.bbox.y2)
+    } else if (this.dir === MOVE_BOTTOM) {
+      points1.y2 = clamp(data.y, data.bbox.y1, data.bbox.middle.y)
+    }
+    this.poly1.setAttribute('points',
+      points1.x1 + ' ' + points1.y1 + ',' +
+      points1.x1 + ' ' + points1.y2 + ',' +
+      points1.x2 + ' ' + points1.y2 + ',' +
+      points1.x2 + ' ' + points1.y1
+    )
+
+    var firstHalf = false
+    var isEnd = (data.puzzle.grid[data.pos.x][data.pos.y].end != null)
+    // The second half of the line uses the raw so that it can enter the endpoint properly.
+    var points2 = JSON.parse(JSON.stringify(data.bbox.raw))
+    if (data.x < data.bbox.middle.x && this.dir !== MOVE_RIGHT) {
+      points2.x1 = clamp(data.x, data.bbox.x1, data.bbox.middle.x)
+      points2.x2 = data.bbox.middle.x
+      if (isEnd && data.pos.x%2 === 0 && data.pos.y%2 === 1) {
+        points2.y1 += 17
+        points2.y2 -= 17
+      }
+    } else if (data.x > data.bbox.middle.x && this.dir !== MOVE_LEFT) {
+      points2.x1 = data.bbox.middle.x
+      points2.x2 = clamp(data.x, data.bbox.middle.x, data.bbox.x2)
+      if (isEnd && data.pos.x%2 === 0 && data.pos.y%2 === 1) {
+        points2.y1 += 17
+        points2.y2 -= 17
+      }
+    } else if (data.y < data.bbox.middle.y && this.dir !== MOVE_BOTTOM) {
+      points2.y1 = clamp(data.y, data.bbox.y1, data.bbox.middle.y)
+      points2.y2 = data.bbox.middle.y
+      if (isEnd && data.pos.x%2 === 1 && data.pos.y%2 === 0) {
+        points2.x1 += 17
+        points2.x2 -= 17
+      }
+    } else if (data.y > data.bbox.middle.y && this.dir !== MOVE_TOP) {
+      points2.y1 = data.bbox.middle.y
+      points2.y2 = clamp(data.y, data.bbox.middle.y, data.bbox.y2)
+      if (isEnd && data.pos.x%2 === 1 && data.pos.y%2 === 0) {
+        points2.x1 += 17
+        points2.x2 -= 17
+      }
+    } else {
+      firstHalf = true
+    }
+
+    this.poly2.setAttribute('points',
+      points2.x1 + ' ' + points2.y1 + ',' +
+      points2.x1 + ' ' + points2.y2 + ',' +
+      points2.x2 + ' ' + points2.y2 + ',' +
+      points2.x2 + ' ' + points2.y1
+    )
+
+    // Show the second poly only in the second half of the cell
+    this.poly2.setAttribute('opacity', (firstHalf ? 0 : 1))
+    // Show the circle in the second half of the cell AND in the start
+    if (firstHalf && this.dir !== MOVE_NONE) {
+      this.circ.setAttribute('opacity', 0)
+    } else {
+      this.circ.setAttribute('opacity', 1)
+    }
+
+    // Draw the symmetrical path based on the original one
+    if (data.puzzle.symmetry != null) {
+      this.symPoly1.setAttribute('points',
+        this._reflX(points1.x2) + ' ' + this._reflY(points1.y2) + ',' +
+        this._reflX(points1.x2) + ' ' + this._reflY(points1.y1) + ',' +
+        this._reflX(points1.x1) + ' ' + this._reflY(points1.y1) + ',' +
+        this._reflX(points1.x1) + ' ' + this._reflY(points1.y2)
+      )
+
+      this.symPoly2.setAttribute('points',
+        this._reflX(points2.x2) + ' ' + this._reflY(points2.y2) + ',' +
+        this._reflX(points2.x2) + ' ' + this._reflY(points2.y1) + ',' +
+        this._reflX(points2.x1) + ' ' + this._reflY(points2.y1) + ',' +
+        this._reflX(points2.x1) + ' ' + this._reflY(points2.y2)
+      )
+
+      this.symCirc.setAttribute('opacity', this.circ.getAttribute('opacity'))
+      this.symPoly2.setAttribute('opacity', this.poly2.getAttribute('opacity'))
+    }
+  }
+
+  _reflX(x) {
+    if (data.puzzle.symmetry == null) return x
+    if (data.puzzle.symmetry.x === true) {
+      // Mirror position inside the bounding box
+      return (data.bbox.middle.x - x) + data.symbbox.middle.x
+    }
+    // Copy position inside the bounding box
+    return (x - data.bbox.middle.x) + data.symbbox.middle.x
+  }
+
+  _reflY(y) {
+    if (data.puzzle.symmetry == null) return y
+    if (data.puzzle.symmetry.y === true) {
+      // Mirror position inside the bounding box
+      return (data.bbox.middle.y - y) + data.symbbox.middle.y
+    }
+    // Copy position inside the bounding box
+    return (y - data.bbox.middle.y) + data.symbbox.middle.y
+  }
+}
+
+var data = {}
+
+function clearGrid(svg, puzzle) {
+  if (data.bbox != null && data.bbox.debug != null) {
+    data.svg.removeChild(data.bbox.debug)
+    data.bbox = null
+  }
+  if (data.symbbox != null && data.symbbox.debug != null) {
+    data.svg.removeChild(data.symbbox.debug)
+    data.symbbox = null
+  }
+
+  window.deleteElementsByClassName(svg, 'cursor')
+  window.deleteElementsByClassName(svg, 'line-1')
+  window.deleteElementsByClassName(svg, 'line-2')
+  window.deleteElementsByClassName(svg, 'line-3')
+  puzzle.clearLines()
+}
+
+// This copy is an exact copy of puzzle.getSymmetricalDir, except that it uses MOVE_* values instead of strings
+function getSymmetricalDir(puzzle, dir) {
+  if (puzzle.symmetry != null) {
+    if (puzzle.symmetry.x === true) {
+      if (dir === MOVE_LEFT) return MOVE_RIGHT
+      if (dir === MOVE_RIGHT) return MOVE_LEFT
+    }
+    if (puzzle.symmetry.y === true) {
+      if (dir === MOVE_TOP) return MOVE_BOTTOM
+      if (dir === MOVE_BOTTOM) return MOVE_TOP
+    }
+  }
+  return dir
+}
+
+window.trace = function(event, puzzle, pos, start, symStart=null) {
+  /*if (data.start == null) {*/
+  if (data.tracing !== true) { // could be undefined or false
+    var svg = start.parentElement
+    data.tracing = true
+    window.PLAY_SOUND('start')
+    // Cleans drawn lines & puzzle state
+    clearGrid(svg, puzzle)
+    onTraceStart(puzzle, pos, svg, start, symStart)
+    data.animations.insertRule('.' + svg.id + '.start {animation: 150ms 1 forwards start-grow}\n')
+
+    hookMovementEvents(start)
+  } else {
+    event.stopPropagation()
+    // Signal the onMouseMove to stop accepting input (race condition)
+    data.tracing = false
+
+    // At endpoint and in main box
+    var cell = puzzle.getCell(data.pos.x, data.pos.y)
+    if (cell.end != null && data.bbox.inMain(data.x, data.y)) {
+      data.cursor.onpointerdown = null
+      setTimeout(function() { // Run validation asynchronously so we can free the pointer immediately.
+        puzzle.endPoint = data.pos
+        var puzzleData = window.validate(puzzle, false) // We want all invalid elements so we can show the user.
+
+        for (var negation of puzzleData.negations) {
+          console.debug('Rendering negation', negation)
+          data.animations.insertRule('.' + data.svg.id + '_' + negation.source.x + '_' + negation.source.y + ' {animation: 0.75s 1 forwards fade}\n')
+          data.animations.insertRule('.' + data.svg.id + '_' + negation.target.x + '_' + negation.target.y + ' {animation: 0.75s 1 forwards fade}\n')
+        }
+
+        if (puzzleData.valid()) {
+          window.PLAY_SOUND('success')
+          // !important to override the child animation
+          data.animations.insertRule('.' + data.svg.id + ' {animation: 1s 1 forwards line-success !important}\n')
+
+          // Convert the traced path into something suitable for solve.drawPath (for publishing purposes)
+          var rawPath = [puzzle.startPoint]
+          for (var i=1; i<data.path.length; i++) rawPath.push(data.path[i].dir)
+          rawPath.push(0)
+
+          if (window.TRACE_COMPLETION_FUNC) window.TRACE_COMPLETION_FUNC(puzzle, rawPath)
+        } else {
+          window.PLAY_SOUND('fail')
+          data.animations.insertRule('.' + data.svg.id + ' {animation: 1s 1 forwards line-fail !important}\n')
+          // Get list of invalid elements
+          if (puzzle.settings.FLASH_FOR_ERRORS) {
+            for (var invalidElement of puzzleData.invalidElements) {
+              data.animations.insertRule('.' + data.svg.id + '_' + invalidElement.x + '_' + invalidElement.y + ' {animation: 0.4s 20 alternate-reverse error}\n')
+            }
+          }
+        }
+      }, 1)
+
+    // Right-clicked (or double-tapped) and not at the end: Clear puzzle
+    } else if (event.isRightClick()) {
+      window.PLAY_SOUND('abort')
+      clearGrid(data.svg, puzzle)
+    } else { // Exit lock but allow resuming from the cursor (Desktop only)
+      data.cursor.onpointerdown = function() {
+        if (start.parentElement !== data.svg) return // Another puzzle is live, so data is gone
+        data.tracing = true
+        hookMovementEvents(start)
+      }
+    }
+
+    unhookMovementEvents()
+  }
+}
+
+window.clearAnimations = function() {
+  if (data.animations == null) return
+  for (var i=0; i<data.animations.cssRules.length; i++) {
+    var rule = data.animations.cssRules[i]
+    if (rule.selectorText != null && rule.selectorText.startsWith('.' + data.svg.id)) {
+      data.animations.deleteRule(i--)
+    }
+  }
+}
+
+window.onTraceStart = function(puzzle, pos, svg, start, symStart=null) {
+  var x = parseFloat(start.getAttribute('cx'))
+  var y = parseFloat(start.getAttribute('cy'))
+
+  var cursor = createElement('circle')
+  cursor.setAttribute('r', 12)
+  cursor.setAttribute('fill', window.CURSOR)
+  cursor.setAttribute('stroke', 'black')
+  cursor.setAttribute('stroke-width', '2px')
+  cursor.setAttribute('stroke-opacity', '0.4')
+  cursor.setAttribute('class', 'cursor')
+  cursor.setAttribute('cx', x)
+  cursor.setAttribute('cy', y)
+  svg.insertBefore(cursor, svg.getElementById('cursorPos'))
+
+  data.svg = svg
+  data.cursor = cursor
+  data.x = x
+  data.y = y
+  data.pos = pos
+  data.sym = puzzle.getSymmetricalPos(pos.x, pos.y)
+  data.puzzle = puzzle
+  data.path = []
+  puzzle.startPoint = {'x': pos.x, 'y': pos.y}
+
+  if (pos.x % 2 === 1) { // Start point is on a horizontal segment
+    data.bbox = new BoundingBox(x - 29, x + 29, y - 12, y + 12)
+  } else if (pos.y % 2 === 1) { // Start point is on a vertical segment
+    data.bbox = new BoundingBox(x - 12, x + 12, y - 29, y + 29)
+  } else { // Start point is at an intersection
+    data.bbox = new BoundingBox(x - 12, x + 12, y - 12, y + 12)
+  }
+
+  for (var styleSheet of document.styleSheets) {
+    if (styleSheet.title === 'animations') {
+      data.animations = styleSheet
+      break
+    }
+  }
+
+  clearAnimations()
+
+  // Add initial line segments + secondary symmetry cursor, if needed
+  if (puzzle.symmetry == null) {
+    data.puzzle.updateCell2(data.pos.x, data.pos.y, 'type', 'line')
+    data.puzzle.updateCell2(data.pos.x, data.pos.y, 'line', window.LINE_BLACK)
+  } else {
+    data.puzzle.updateCell2(data.pos.x, data.pos.y, 'type', 'line')
+    data.puzzle.updateCell2(data.pos.x, data.pos.y, 'line', window.LINE_BLUE)
+    data.puzzle.updateCell2(data.sym.x, data.sym.y, 'type', 'line')
+    data.puzzle.updateCell2(data.sym.x, data.sym.y, 'line', window.LINE_YELLOW)
+
+    var dx = parseFloat(symStart.getAttribute('cx')) - data.x
+    var dy = parseFloat(symStart.getAttribute('cy')) - data.y
+    data.symbbox = new BoundingBox(
+      data.bbox.raw.x1 + dx,
+      data.bbox.raw.x2 + dx,
+      data.bbox.raw.y1 + dy,
+      data.bbox.raw.y2 + dy,
+      sym = true)
+
+    data.symcursor = createElement('circle')
+    svg.insertBefore(data.symcursor, data.cursor)
+    data.symcursor.setAttribute('class', 'line-3 ' + data.svg.id)
+    data.symcursor.setAttribute('cx', symStart.getAttribute('cx'))
+    data.symcursor.setAttribute('cy', symStart.getAttribute('cy'))
+    data.symcursor.setAttribute('r', 12)
+  }
+
+  // Fixup: Mark out of bounds cells as null, setting inbounds cells as {}
+  // This allows tracing to correctly identify inbounds cells (and thus interior walls) and correctly handle exterior walls for oddly shaped puzzles.
+  {
+    var savedGrid = data.puzzle.switchToMaskedGrid()
+    var maskedGrid = data.puzzle.grid
+    data.puzzle.grid = savedGrid
+
+    for (var x=1; x<data.puzzle.width; x+=2) {
+      for (var y=1; y<data.puzzle.height; y+=2) {
+        if (maskedGrid[x][y] == null) { // null == MASKED_OOB
+          data.puzzle.grid[x][y] = null
+        } else if (data.puzzle.grid[x][y] == null) {
+          data.puzzle.grid[x][y] = {'type':'nonce'}
+        }
+      }
+    }
+  }
+  data.path.push(new PathSegment(MOVE_NONE)) // Must be created after initializing data.symbbox
+}
+
+// In case the user exit the pointer lock via another means (clicking outside the window, hitting esc, etc)
+// we still need to disengage our tracing hooks.
+document.onpointerlockchange = function() {
+  if (document.pointerLockElement == null) unhookMovementEvents()
+}
+
+function unhookMovementEvents() {
+  data.start = null
+  document.onmousemove = null
+  document.ontouchstart = null
+  document.ontouchmove = null
+  document.ontouchend = null
+  if (document.exitPointerLock != null) document.exitPointerLock()
+  if (document.mozExitPointerLock != null) document.mozExitPointerLock()
+}
+
+function hookMovementEvents(start) {
+  data.start = start
+  if (start.requestPointerLock != null) start.requestPointerLock()
+  if (start.mozRequestPointerLock != null) start.mozRequestPointerLock()
+
+  var sens = parseFloat(document.getElementById('sens').value)
+  document.onmousemove = function(event) {
+    // Working around a race condition where movement events fire after the handler is removed.
+    if (data.tracing !== true) return
+    // Prevent accidental fires on mobile platforms (ios and android). They will be handled via ontouchmove instead.
+    if (event.movementX == null) return
+    onMove(sens * event.movementX, sens * event.movementY)
+  }
+  document.ontouchstart = function(event) {
+    if (event.touches.length > 1) {
+      // Stop tracing for two+ finger touches (the equivalent of a right click on desktop)
+      window.trace(event, data.puzzle, null, null, null)
+      return
+    }
+    data.lastTouchPos = event.position
+  }
+  document.ontouchmove = function(event) {
+    if (data.tracing !== true) return
+
+    var eventIsWithinPuzzle = false
+    for (var node = event.target; node != null; node = node.parentElement) {
+      if (node == data.svg) {
+        eventIsWithinPuzzle = true
+        break
+      }
+    }
+    if (!eventIsWithinPuzzle) return // Ignore drag events that aren't within the puzzle
+    event.preventDefault() // Prevent accidental scrolling if the touch event is within the puzzle.
+
+    var newPos = event.position
+    onMove(newPos.x - data.lastTouchPos.x, newPos.y - data.lastTouchPos.y)
+    data.lastTouchPos = newPos
+  }
+  document.ontouchend = function(event) {
+    data.lastTouchPos = null
+    // Only call window.trace (to stop tracing) if we're really in an endpoint.
+    var cell = data.puzzle.getCell(data.pos.x, data.pos.y)
+    if (cell.end != null && data.bbox.inMain(data.x, data.y)) {
+      window.trace(event, data.puzzle, null, null, null)
+    }
+  }
+}
+
+// @Volatile -- must match order of PATH_* in solve
+var MOVE_NONE   = 0
+var MOVE_LEFT   = 1
+var MOVE_RIGHT  = 2
+var MOVE_TOP    = 3
+var MOVE_BOTTOM = 4
+
+window.onMove = function(dx, dy) {
+  {
+    // Also handles some collision
+    var collidedWith = pushCursor(dx, dy)
+    console.spam('Collided with', collidedWith)
+  }
+
+  while (true) {
+    hardCollision()
+
+    // Potentially move the location to a new cell, and make absolute boundary checks
+    var moveDir = move()
+    data.path[data.path.length - 1].redraw()
+    if (moveDir === MOVE_NONE) break
+    console.debug('Moved', ['none', 'left', 'right', 'top', 'bottom'][moveDir])
+
+    // Potentially adjust data.x/data.y if our position went around a pillar
+    if (data.puzzle.pillar === true) pillarWrap(moveDir)
+
+    var lastDir = data.path[data.path.length - 1].dir
+    var backedUp = ((moveDir === MOVE_LEFT && lastDir === MOVE_RIGHT)
+                 || (moveDir === MOVE_RIGHT && lastDir === MOVE_LEFT)
+                 || (moveDir === MOVE_TOP && lastDir === MOVE_BOTTOM)
+                 || (moveDir === MOVE_BOTTOM && lastDir === MOVE_TOP))
+
+    if (data.puzzle.symmetry != null) {
+      var symMoveDir = getSymmetricalDir(data.puzzle, moveDir)
+    }
+
+    // If we backed up, remove a path segment and mark the old cell as unvisited
+    if (backedUp) {
+      data.path.pop().destroy()
+      data.puzzle.updateCell2(data.pos.x, data.pos.y, 'line', window.LINE_NONE)
+      if (data.puzzle.symmetry != null) {
+        data.puzzle.updateCell2(data.sym.x, data.sym.y, 'line', window.LINE_NONE)
+      }
+    }
+
+    // Move to the next cell
+    changePos(data.bbox, data.pos, moveDir)
+    if (data.puzzle.symmetry != null) {
+      changePos(data.symbbox, data.sym, symMoveDir)
+    }
+
+    // If we didn't back up, add a path segment and mark the new cell as visited
+    if (!backedUp) {
+      data.path.push(new PathSegment(moveDir))
+      if (data.puzzle.symmetry == null) {
+        data.puzzle.updateCell2(data.pos.x, data.pos.y, 'line', window.LINE_BLACK)
+      } else {
+        data.puzzle.updateCell2(data.pos.x, data.pos.y, 'line', window.LINE_BLUE)
+        data.puzzle.updateCell2(data.sym.x, data.sym.y, 'line', window.LINE_YELLOW)
+      }
+    }
+  }
+}
+
+// Helper function for pushCursor. Used to determine the direction and magnitude of redirection.
+function push(dx, dy, dir, targetDir) {
+  // Fraction of movement to redirect in the other direction
+  var movementRatio = null
+  if (targetDir === 'left' || targetDir === 'top') {
+    movementRatio = -3
+  } else if (targetDir === 'right' || targetDir === 'bottom') {
+    movementRatio = 3
+  }
+  if (window.settings.disablePushing === true) movementRatio *= 1000
+
+  if (dir === 'left') {
+    var overshoot = data.bbox.x1 - (data.x + dx) + 12
+    if (overshoot > 0) {
+      data.y += dy + overshoot / movementRatio
+      data.x = data.bbox.x1 + 12
+      return true
+    }
+  } else if (dir === 'right') {
+    var overshoot = (data.x + dx) - data.bbox.x2 + 12
+    if (overshoot > 0) {
+      data.y += dy + overshoot / movementRatio
+      data.x = data.bbox.x2 - 12
+      return true
+    }
+  } else if (dir === 'leftright') {
+    data.y += dy + Math.abs(dx) / movementRatio
+    return true
+  } else if (dir === 'top') {
+    var overshoot = data.bbox.y1 - (data.y + dy) + 12
+    if (overshoot > 0) {
+      data.x += dx + overshoot / movementRatio
+      data.y = data.bbox.y1 + 12
+      return true
+    }
+  } else if (dir === 'bottom') {
+    var overshoot = (data.y + dy) - data.bbox.y2 + 12
+    if (overshoot > 0) {
+      data.x += dx + overshoot / movementRatio
+      data.y = data.bbox.y2 - 12
+      return true
+    }
+  } else if (dir === 'topbottom') {
+    data.x += dx + Math.abs(dy) / movementRatio
+    return true
+  }
+  return false
+}
+
+// Redirect momentum from pushing against walls, so that all further moment steps
+// will be strictly linear. Returns a string for logging purposes only.
+function pushCursor(dx, dy) {
+  // Outer wall collision
+  var cell = data.puzzle.getCell(data.pos.x, data.pos.y)
+  if (cell == null) return 'nothing'
+
+  // Only consider non-endpoints or endpoints which are parallel
+  if ([undefined, 'top', 'bottom'].includes(cell.end)) {
+    var leftCell = data.puzzle.getCell(data.pos.x - 1, data.pos.y)
+    if (leftCell == null || leftCell.gap === window.GAP_FULL) {
+      if (push(dx, dy, 'left', 'top')) return 'left outer wall'
+    }
+    var rightCell = data.puzzle.getCell(data.pos.x + 1, data.pos.y)
+    if (rightCell == null || rightCell.gap === window.GAP_FULL) {
+      if (push(dx, dy, 'right', 'top')) return 'right outer wall'
+    }
+  }
+  // Only consider non-endpoints or endpoints which are parallel
+  if ([undefined, 'left', 'right'].includes(cell.end)) {
+    var topCell = data.puzzle.getCell(data.pos.x, data.pos.y - 1)
+    if (topCell == null || topCell.gap === window.GAP_FULL) {
+      if (push(dx, dy, 'top', 'right')) return 'top outer wall'
+    }
+    var bottomCell = data.puzzle.getCell(data.pos.x, data.pos.y + 1)
+    if (bottomCell == null || bottomCell.gap === window.GAP_FULL) {
+      if (push(dx, dy, 'bottom', 'right')) return 'bottom outer wall'
+    }
+  }
+
+  // Inner wall collision
+  if (cell.end == null) {
+    if (data.pos.x%2 === 1 && data.pos.y%2 === 0) { // Horizontal cell
+      if (data.x < data.bbox.middle.x) {
+        push(dx, dy, 'topbottom', 'left')
+        return 'topbottom inner wall, moved left'
+      } else {
+        push(dx, dy, 'topbottom', 'right')
+        return 'topbottom inner wall, moved right'
+      }
+    } else if (data.pos.x%2 === 0 && data.pos.y%2 === 1) { // Vertical cell
+      if (data.y < data.bbox.middle.y) {
+        push(dx, dy, 'leftright', 'top')
+        return 'leftright inner wall, moved up'
+      } else {
+        push(dx, dy, 'leftright', 'bottom')
+        return 'leftright inner wall, moved down'
+      }
+    }
+  }
+
+  // Intersection & endpoint collision
+  // Ratio of movement to be considered turning at an intersection
+  var turnMod = 2
+  if ((data.pos.x%2 === 0 && data.pos.y%2 === 0) || cell.end != null) {
+    if (data.x < data.bbox.middle.x) {
+      push(dx, dy, 'topbottom', 'right')
+      // Overshot the intersection and appears to be trying to turn
+      if (data.x > data.bbox.middle.x && Math.abs(dy) * turnMod > Math.abs(dx)) {
+        data.y += Math.sign(dy) * (data.x - data.bbox.middle.x)
+        data.x = data.bbox.middle.x
+        return 'overshot moving right'
+      }
+      return 'intersection moving right'
+    } else if (data.x > data.bbox.middle.x) {
+      push(dx, dy, 'topbottom', 'left')
+      // Overshot the intersection and appears to be trying to turn
+      if (data.x < data.bbox.middle.x && Math.abs(dy) * turnMod > Math.abs(dx)) {
+        data.y += Math.sign(dy) * (data.bbox.middle.x - data.x)
+        data.x = data.bbox.middle.x
+        return 'overshot moving left'
+      }
+      return 'intersection moving left'
+    }
+    if (data.y < data.bbox.middle.y) {
+      push(dx, dy, 'leftright', 'bottom')
+      // Overshot the intersection and appears to be trying to turn
+      if (data.y > data.bbox.middle.y && Math.abs(dx) * turnMod > Math.abs(dy)) {
+        data.x += Math.sign(dx) * (data.y - data.bbox.middle.y)
+        data.y = data.bbox.middle.y
+        return 'overshot moving down'
+      }
+      return 'intersection moving down'
+    } else if (data.y > data.bbox.middle.y) {
+      push(dx, dy, 'leftright', 'top')
+      // Overshot the intersection and appears to be trying to turn
+      if (data.y < data.bbox.middle.y && Math.abs(dx) * turnMod > Math.abs(dy)) {
+        data.x += Math.sign(dx) * (data.bbox.middle.y - data.y)
+        data.y = data.bbox.middle.y
+        return 'overshot moving up'
+      }
+      return 'intersection moving up'
+    }
+  }
+
+  // No collision, limit movement to X or Y only to prevent out-of-bounds
+  if (Math.abs(dx) > Math.abs(dy)) {
+    data.x += dx
+    return 'nothing, x'
+  } else {
+    data.y += dy
+    return 'nothing, y'
+  }
+}
+
+// Check to see if we collided with any gaps, or with a symmetrical line, or a startpoint.
+// In any case, abruptly zero momentum.
+function hardCollision() {
+  var lastDir = data.path[data.path.length - 1].dir
+  var cell = data.puzzle.getCell(data.pos.x, data.pos.y)
+  if (cell == null) return
+
+  var gapSize = 0
+  if (cell.gap === window.GAP_BREAK) {
+    console.spam('Collided with a gap')
+    gapSize = 21
+  } else {
+    var nextCell = null
+    if (lastDir === MOVE_LEFT)   nextCell = data.puzzle.getCell(data.pos.x - 1, data.pos.y)
+    if (lastDir === MOVE_RIGHT)  nextCell = data.puzzle.getCell(data.pos.x + 1, data.pos.y)
+    if (lastDir === MOVE_TOP)    nextCell = data.puzzle.getCell(data.pos.x, data.pos.y - 1)
+    if (lastDir === MOVE_BOTTOM) nextCell = data.puzzle.getCell(data.pos.x, data.pos.y + 1)
+    if (nextCell != null && nextCell.start === true && nextCell.line > window.LINE_NONE) {
+      gapSize = -5
+    }
+  }
+
+  if (data.puzzle.symmetry != null) {
+    if (data.sym.x === data.pos.x && data.sym.y === data.pos.y) {
+      console.spam('Collided with our symmetrical line')
+      gapSize = 13
+    } else if (data.puzzle.getCell(data.sym.x, data.sym.y).gap === window.GAP_BREAK) {
+      console.spam('Symmetrical line hit a gap')
+      gapSize = 21
+    }
+  }
+  if (gapSize === 0) return // Didn't collide with anything
+
+  if (lastDir === MOVE_LEFT) {
+    data.x = Math.max(data.bbox.middle.x + gapSize, data.x)
+  } else if (lastDir === MOVE_RIGHT) {
+    data.x = Math.min(data.x, data.bbox.middle.x - gapSize)
+  } else if (lastDir === MOVE_TOP) {
+    data.y = Math.max(data.bbox.middle.y + gapSize, data.y)
+  } else if (lastDir === MOVE_BOTTOM) {
+    data.y = Math.min(data.y, data.bbox.middle.y - gapSize)
+  }
+}
+
+// Check to see if we've gone beyond the edge of puzzle cell, and if the next cell is safe,
+// i.e. not out of bounds. Reports the direction we are going to move (or none),
+// but does not actually change data.pos
+function move() {
+  var lastDir = data.path[data.path.length - 1].dir
+
+  if (data.x < data.bbox.x1 + 12) { // Moving left
+    var cell = data.puzzle.getCell(data.pos.x - 1, data.pos.y)
+    if (cell == null || cell.type !== 'line' || cell.gap === window.GAP_FULL) {
+      console.spam('Collided with outside / gap-2', cell)
+      data.x = data.bbox.x1 + 12
+    } else if (cell.line > window.LINE_NONE && lastDir !== MOVE_RIGHT) {
+      console.spam('Collided with other line', cell.line)
+      data.x = data.bbox.x1 + 12
+    } else if (data.puzzle.symmetry != null) {
+      var symCell = data.puzzle.getSymmetricalCell(data.pos.x - 1, data.pos.y)
+      if (symCell == null || symCell.type !== 'line' || symCell.gap === window.GAP_FULL) {
+        console.spam('Collided with symmetrical outside / gap-2', cell)
+        data.x = data.bbox.x1 + 12
+      }
+    }
+    if (data.x < data.bbox.x1) {
+      return MOVE_LEFT
+    }
+  } else if (data.x > data.bbox.x2 - 12) { // Moving right
+    var cell = data.puzzle.getCell(data.pos.x + 1, data.pos.y)
+    if (cell == null || cell.type !== 'line' || cell.gap === window.GAP_FULL) {
+      console.spam('Collided with outside / gap-2', cell)
+      data.x = data.bbox.x2 - 12
+    } else if (cell.line > window.LINE_NONE && lastDir !== MOVE_LEFT) {
+      console.spam('Collided with other line', cell.line)
+      data.x = data.bbox.x2 - 12
+    } else if (data.puzzle.symmetry != null) {
+      var symCell = data.puzzle.getSymmetricalCell(data.pos.x + 1, data.pos.y)
+      if (symCell == null || symCell.type !== 'line' || symCell.gap === window.GAP_FULL) {
+        console.spam('Collided with symmetrical outside / gap-2', cell)
+        data.x = data.bbox.x2 - 12
+      }
+    }
+    if (data.x > data.bbox.x2) {
+      return MOVE_RIGHT
+    }
+  } else if (data.y < data.bbox.y1 + 12) { // Moving up
+    var cell = data.puzzle.getCell(data.pos.x, data.pos.y - 1)
+    if (cell == null || cell.type !== 'line' || cell.gap === window.GAP_FULL) {
+      console.spam('Collided with outside / gap-2', cell)
+      data.y = data.bbox.y1 + 12
+    } else if (cell.line > window.LINE_NONE && lastDir !== MOVE_BOTTOM) {
+      console.spam('Collided with other line', cell.line)
+      data.y = data.bbox.y1 + 12
+    } else if (data.puzzle.symmetry != null) {
+      var symCell = data.puzzle.getSymmetricalCell(data.pos.x, data.pos.y - 1)
+      if (symCell == null || symCell.type !== 'line' || symCell.gap === window.GAP_FULL) {
+        console.spam('Collided with symmetrical outside / gap-2', cell)
+        data.y = data.bbox.y1 + 12
+      }
+    }
+    if (data.y < data.bbox.y1) {
+      return MOVE_TOP
+    }
+  } else if (data.y > data.bbox.y2 - 12) { // Moving down
+    var cell = data.puzzle.getCell(data.pos.x, data.pos.y + 1)
+    if (cell == null || cell.type !== 'line' || cell.gap === window.GAP_FULL) {
+      console.spam('Collided with outside / gap-2')
+      data.y = data.bbox.y2 - 12
+    } else if (cell.line > window.LINE_NONE && lastDir !== MOVE_TOP) {
+      console.spam('Collided with other line', cell.line)
+      data.y = data.bbox.y2 - 12
+    } else if (data.puzzle.symmetry != null) {
+      var symCell = data.puzzle.getSymmetricalCell(data.pos.x, data.pos.y + 1)
+      if (symCell == null || symCell.type !== 'line' || symCell.gap === window.GAP_FULL) {
+        console.spam('Collided with symmetrical outside / gap-2', cell)
+        data.y = data.bbox.y2 - 12
+      }
+    }
+    if (data.y > data.bbox.y2) {
+      return MOVE_BOTTOM
+    }
+  }
+  return MOVE_NONE
+}
+
+// Check to see if you moved beyond the edge of a pillar.
+// If so, wrap the cursor x to preserve momentum.
+// Note that this still does not change the position.
+function pillarWrap(moveDir) {
+  if (moveDir === MOVE_LEFT && data.pos.x === 0) {
+    data.x += data.puzzle.width * 41
+  }
+  if (moveDir === MOVE_RIGHT && data.pos.x === data.puzzle.width - 1) {
+    data.x -= data.puzzle.width * 41
+  }
+}
+
+// Actually change the data position. (Note that this takes in pos to allow easier symmetry).
+// Note that this doesn't zero the momentum, so that we can adjust appropriately on further loops.
+// This function also shifts the bounding box that we use to determine the bounds of the cell.
+function changePos(bbox, pos, moveDir) {
+  if (moveDir === MOVE_LEFT) {
+    pos.x--
+    // Wrap around the left
+    if (data.puzzle.pillar === true && pos.x < 0) {
+      pos.x += data.puzzle.width
+      bbox.shift('right', data.puzzle.width * 41 - 82)
+      bbox.shift('right', 58)
+    } else {
+      bbox.shift('left', (pos.x%2 === 0 ? 24 : 58))
+    }
+  } else if (moveDir === MOVE_RIGHT) {
+    pos.x++
+    // Wrap around to the right
+    if (data.puzzle.pillar === true && pos.x >= data.puzzle.width) {
+      pos.x -= data.puzzle.width
+      bbox.shift('left', data.puzzle.width * 41 - 82)
+      bbox.shift('left', 24)
+    } else {
+      bbox.shift('right', (pos.x%2 === 0 ? 24 : 58))
+    }
+  } else if (moveDir === MOVE_TOP) {
+    pos.y--
+    bbox.shift('top', (pos.y%2 === 0 ? 24 : 58))
+  } else if (moveDir === MOVE_BOTTOM) {
+    pos.y++
+    bbox.shift('bottom', (pos.y%2 === 0 ? 24 : 58))
+  }
+}
+
+})
@@ -0,0 +1,697 @@
+function namespace(code) {
+  code()
+}
+
+namespace(function() {
+
+/*** Start cross-compatibility ***/
+// Used to detect if IDs include a direction, e.g. resize-top-left
+if (!String.prototype.includes) {
+  String.prototype.includes = function() {
+    return String.prototype.indexOf.apply(this, arguments) !== -1
+  }
+}
+Event.prototype.movementX = Event.prototype.movementX || Event.prototype.mozMovementX
+Event.prototype.movementY = Event.prototype.movementY || Event.prototype.mozMovementY
+Event.prototype.isRightClick = function() {
+  return this.which === 3 || (this.touches && this.touches.length > 1)
+}
+Element.prototype.disable = function() {
+  this.disabled = true
+  this.style.pointerEvents = 'none'
+  this.className = 'noselect'
+}
+Element.prototype.enable = function() {
+  this.disabled = false
+  this.style.pointerEvents = null
+  this.className = null
+}
+Object.defineProperty(Event.prototype, 'position', {
+  'get': function() {
+    return {
+      'x': event.pageX || event.clientX || (event.touches && event.touches[0].pageX) || null,
+      'y': event.pageY || event.clientY || (event.touches && event.touches[0].pageY) || null,
+    }
+  }
+})
+/*** End cross-compatibility ***/
+
+var proxy = {
+  'get': function(_, key) {
+    try {
+      return this._map[key]
+    } catch (e) {
+      return null
+    }
+  },
+  'set': function(_, key, value) {
+    if (value == null) {
+      delete this._map[key]
+    } else {
+      this._map[key] = value.toString()
+      window.localStorage.setItem('settings', JSON.stringify(this._map))
+    }
+  },
+  'init': function() {
+    this._map = {}
+    try {
+      var j = window.localStorage.getItem('settings')
+      if (j != null) this._map = JSON.parse(j)
+    } catch (e) {/* Do nothing */}
+
+    function setIfNull(map, key, value) {
+      if (map[key] == null) map[key] = value
+    }
+
+    // Set any values which are not defined
+    setIfNull(this._map, 'theme', 'light')
+    setIfNull(this._map, 'volume', '0.12')
+    setIfNull(this._map, 'sensitivity', '0.7')
+    setIfNull(this._map, 'expanded', 'false')
+    setIfNull(this._map, 'customMechanics', 'false')
+    return this
+  },
+}
+window.settings = new Proxy({}, proxy.init())
+
+var tracks = {
+  'start':   new Audio(src = '<%= asset_url("wittle/panel_start_tracing.aac") %>'),
+  'success': new Audio(src = '<%= asset_url("wittle/panel_success.aac") %>'),
+  'fail':    new Audio(src = '<%= asset_url("wittle/panel_failure.aac") %>'),
+  'abort':   new Audio(src = '<%= asset_url("wittle/panel_abort_tracing.aac") %>'),
+}
+
+var currentAudio = null
+window.PLAY_SOUND = function(name) {
+  if (currentAudio) currentAudio.pause()
+  var audio = tracks[name]
+  audio.load()
+  audio.volume = parseFloat(window.settings.volume)
+  audio.play().then(function() {
+    currentAudio = audio
+  }).catch(function() {
+    // Do nothing.
+  })
+}
+
+window.LINE_PRIMARY = '#8FF'
+window.LINE_SECONDARY = '#FF2'
+
+if (window.settings.theme == 'night') {
+  window.BACKGROUND       = '#221'
+  window.OUTER_BACKGROUND = '#070704'
+  window.FOREGROUND       = '#751'
+  window.BORDER           = '#666'
+  window.LINE_DEFAULT     = '#888'
+  window.LINE_SUCCESS     = '#BBB'
+  window.LINE_FAIL        = '#000'
+  window.CURSOR           = '#FFF'
+  window.TEXT_COLOR       = '#AAA'
+  window.PAGE_BACKGROUND  = '#000'
+  window.ALT_BACKGROUND   = '#333' // An off-black. Good for mild contrast.
+  window.ACTIVE_COLOR     = '#555' // Color for 'while the element is being pressed'
+} else if (window.settings.theme == 'light') {
+  window.BACKGROUND       = '#0A8'
+  window.OUTER_BACKGROUND = '#113833'
+  window.FOREGROUND       = '#344'
+  window.BORDER           = '#000'
+  window.LINE_DEFAULT     = '#AAA'
+  window.LINE_SUCCESS     = '#FFF'
+  window.LINE_FAIL        = '#000'
+  window.CURSOR           = '#FFF'
+  window.TEXT_COLOR       = '#000'
+  window.PAGE_BACKGROUND  = '#FFF'
+  window.ALT_BACKGROUND   = '#EEE' // An off-white. Good for mild contrast.
+  window.ACTIVE_COLOR     = '#DDD' // Color for 'while the element is being pressed'
+}
+
+window.LINE_NONE     = 0
+window.LINE_BLACK    = 1
+window.LINE_BLUE     = 2
+window.LINE_YELLOW   = 3
+window.DOT_NONE      = 0
+window.DOT_BLACK     = 1
+window.DOT_BLUE      = 2
+window.DOT_YELLOW    = 3
+window.DOT_INVISIBLE = 4
+window.GAP_NONE      = 0
+window.GAP_BREAK     = 1
+window.GAP_FULL      = 2
+
+var animations = ''
+var l = function(line) {animations += line + '\n'}
+// pointer-events: none; allows for events to bubble up (so that editor hooks still work)
+l('.line-1 {')
+l('  fill: ' + window.LINE_DEFAULT + ';')
+l('  pointer-events: none;')
+l('}')
+l('.line-2 {')
+l('  fill: ' + window.LINE_PRIMARY + ';')
+l('  pointer-events: none;')
+l('}')
+l('.line-3 {')
+l('  fill: ' + window.LINE_SECONDARY + ';')
+l('  pointer-events: none;')
+l('}')
+l('@keyframes line-success {to {fill: ' + window.LINE_SUCCESS + ';}}')
+l('@keyframes line-fail {to {fill: ' + window.LINE_FAIL + ';}}')
+l('@keyframes error {to {fill: red;}}')
+l('@keyframes fade {to {opacity: 0.35;}}')
+l('@keyframes start-grow {from {r:12;} to {r:24;}}')
+// Neutral button style
+l('button {')
+l('  background-color: ' + window.ALT_BACKGROUND + ';')
+l('  border: 1px solid ' + window.BORDER + ';')
+l('  border-radius: 2px;')
+l('  color: ' + window.TEXT_COLOR + ';')
+l('  display: inline-block;')
+l('  margin: 0px;')
+l('  outline: none;')
+l('  opacity: 1.0;')
+l('  padding: 1px 6px;')
+l('  -moz-appearance: none;')
+l('  -webkit-appearance: none;')
+l('}')
+// Active (while held down) button style
+l('button:active {background-color: ' + window.ACTIVE_COLOR + ';}')
+// Disabled button style
+l('button:disabled {opacity: 0.5;}')
+// Selected button style (see https://stackoverflow.com/a/63108630)
+l('button:focus {outline: none;}')
+l = null
+
+var style = document.createElement('style')
+style.type = 'text/css'
+style.title = 'animations'
+style.appendChild(document.createTextNode(animations))
+document.head.appendChild(style)
+
+// Custom logging to allow leveling
+var consoleError = console.error
+var consoleWarn = console.warn
+var consoleInfo = console.log
+var consoleLog = console.log
+var consoleDebug = console.log
+var consoleSpam = console.log
+var consoleGroup = console.group
+var consoleGroupEnd = console.groupEnd
+
+window.setLogLevel = function(level) {
+  console.error = function() {}
+  console.warn = function() {}
+  console.info = function() {}
+  console.log = function() {}
+  console.debug = function() {}
+  console.spam = function() {}
+  console.group = function() {}
+  console.groupEnd = function() {}
+
+  if (level === 'none') return
+
+  // Instead of throw, but still red flags and is easy to find
+  console.error = consoleError
+  if (level === 'error') return
+
+  // Less serious than error, but flagged nonetheless
+  console.warn = consoleWarn
+  if (level === 'warn') return
+
+  // Default visible, important information
+  console.info = consoleInfo
+  if (level === 'info') return
+
+  // Useful for debugging (mainly validation)
+  console.log = consoleLog
+  if (level === 'log') return
+
+  // Useful for serious debugging (mainly graphics/misc)
+  console.debug = consoleDebug
+  if (level === 'debug') return
+
+  // Useful for insane debugging (mainly tracing/recursion)
+  console.spam = consoleSpam
+  console.group = consoleGroup
+  console.groupEnd = consoleGroupEnd
+  if (level === 'spam') return
+}
+setLogLevel('info')
+
+window.deleteElementsByClassName = function(rootElem, className) {
+  var elems = []
+  while (true) {
+    elems = rootElem.getElementsByClassName(className)
+    if (elems.length === 0) break
+    elems[0].remove()
+  }
+}
+
+window.loadHeader = function(titleText) {
+  document.body.style.marginLeft = '0px'
+
+  var navbar = document.createElement('div')
+  document.body.appendChild(navbar)
+  navbar.className = 'navbar'
+  navbar.style = 'min-width: 700px; position: absolute; top: 0; width: 100%; z-index: 1'
+  navbar.style.borderBottom = '2px solid ' + window.BORDER
+  navbar.style.background = window.PAGE_BACKGROUND
+
+  var navbarPadding = document.createElement('div')
+  document.body.appendChild(navbarPadding)
+  navbarPadding.className = 'navbar-padding'
+
+  var titleDiv = document.createElement('div')
+  navbar.appendChild(titleDiv)
+  titleDiv.style = 'position: absolute; width: 100%; pointer-events: none'
+
+  var titleLabel = document.createElement('label')
+  titleDiv.appendChild(titleLabel)
+  titleLabel.style = 'font-size: 48; pointer-events: auto'
+  titleLabel.id = 'title'
+  titleLabel.innerText = titleText
+
+  var link = document.createElement('label')
+  navbar.appendChild(link)
+  link.style = 'float: left; margin-left: 32px; cursor: pointer; line-height: 60px'
+  link.className = 'navbar-content'
+
+  if (window.location.href.endsWith('browse.html')) {
+    navbar.style.position = 'fixed' // When browsing, pin the navbar to the top so that it's visible during infinite scroll.
+
+    link.innerText = 'Create a puzzle'
+    link.onpointerdown = function() {window.location = 'editor.html'}
+
+    var link2 = document.createElement('label')
+    navbar.appendChild(link2)
+    link2.style = 'float: left; margin-left: 20px; cursor: pointer; line-height: 60px; display: none'
+    link2.className = 'navbar-content'
+    link2.innerText = 'Jump to top'
+    link2.id = 'scrollToTop'
+    link2.onpointerdown = function() {window.scrollTo(0, 0)}
+
+  } else if (window.location.href.includes('/play/')) {
+    link.innerText = 'Back to all puzzles'
+    link.onpointerdown = function() {window.location = '../browse.html'}
+  } else /* All other pages */ {
+    link.innerText = 'Browse all puzzles'
+    link.onpointerdown = function() {window.location = 'browse.html'}
+  }
+
+  var feedbackButton = document.createElement('label')
+  navbar.appendChild(feedbackButton)
+  feedbackButton.id = 'feedbackButton'
+  feedbackButton.style = 'float: right; margin-right: 8px; cursor: pointer; line-height: 60px'
+  feedbackButton.innerText = 'Send feedback'
+  feedbackButton.className = 'navbar-content'
+  feedbackButton.onpointerdown = function() {
+    var feedback = prompt('Provide feedback:')
+    if (feedback) {
+      sendFeedback(feedback)
+    }
+  }
+
+  var separator = document.createElement('label')
+  navbar.appendChild(separator)
+  separator.style = 'float: right; line-height: 60px; padding-left: 6px; padding-right: 6px'
+  separator.className = 'navbar-content'
+  separator.innerText = '|'
+
+  var sourceLink = document.createElement('label')
+  navbar.appendChild(sourceLink)
+  sourceLink.style = 'float: right; line-height: 60px; cursor: pointer'
+  sourceLink.innerText = 'Source code'
+  sourceLink.className = 'navbar-content'
+  sourceLink.onpointerdown = function() {window.open('https://github.com/jbzdarkid/jbzdarkid.github.io', '_blank')}
+
+  var collapsedSettings = drawSymbol({'type': 'plus', 'width':20, 'height':20})
+  navbar.appendChild(collapsedSettings)
+  collapsedSettings.style = 'width: 20px; height: 20px; position: absolute; left: 0; cursor: pointer'
+  collapsedSettings.style.border = '2px solid ' + window.BORDER
+  collapsedSettings.id = 'collapsedSettings'
+  collapsedSettings.onpointerdown = function() {
+    this.style.display = 'none'
+    var expandedSettings = document.getElementById('expandedSettings')
+    expandedSettings.style.display = null
+    window.settings.expanded = 'true'
+  }
+
+  var expandedSettings = document.createElement('div')
+  navbar.appendChild(expandedSettings)
+  expandedSettings.style = 'width: 300px; position: absolute; left: 0; display: none; padding: 10px'
+  expandedSettings.style.border = '2px solid ' + window.BORDER
+  expandedSettings.style.background = window.PAGE_BACKGROUND
+  expandedSettings.id = 'expandedSettings'
+
+  var minus = drawSymbol({'type':'minus', 'width':20, 'height':20})
+  minus.style = 'width: 20px; height: 20px; cursor: pointer; position: absolute; top: 0; left: 0'
+  expandedSettings.appendChild(minus)
+  minus.onpointerdown = function() {
+    this.parentElement.style.display = 'none'
+    var collapsedSettings = document.getElementById('collapsedSettings')
+    collapsedSettings.style.display = null
+    window.settings.expanded = 'false'
+  }
+
+  if (window.settings.expanded == 'true') {
+    collapsedSettings.onpointerdown()
+  }
+
+  // Now, for the contents of the settings
+  var settingsLabel = document.createElement('label')
+  expandedSettings.appendChild(settingsLabel)
+  settingsLabel.innerText = 'settings'
+  settingsLabel.style = 'line-height: 0px' // Attach to the top
+
+  expandedSettings.appendChild(document.createElement('br'))
+  expandedSettings.appendChild(document.createElement('br'))
+
+  // Theme
+  document.body.style.color = window.TEXT_COLOR
+  document.body.style.background = window.PAGE_BACKGROUND
+  var themeButton = document.createElement('button')
+  expandedSettings.appendChild(themeButton)
+  if (window.settings.theme == 'night') {
+    themeButton.innerText = 'Night theme'
+    themeButton.onpointerdown = function() {
+      window.settings.theme = 'light'
+      location.reload()
+    }
+  } else if (window.settings.theme == 'light') {
+    themeButton.innerText = 'Light theme'
+    themeButton.onpointerdown = function() {
+      window.settings.theme = 'night'
+      location.reload()
+    }
+  }
+
+  expandedSettings.appendChild(document.createElement('br'))
+
+  // Sensitivity
+  var sensLabel = document.createElement('label')
+  expandedSettings.appendChild(sensLabel)
+  sensLabel.htmlFor = 'sens'
+  sensLabel.innerText = 'Mouse Speed 2D'
+
+  var sens = document.createElement('input')
+  expandedSettings.appendChild(sens)
+  sens.type = 'range'
+  sens.id = 'sens'
+  sens.min = '0.1'
+  sens.max = '1.3'
+  sens.step = '0.1'
+  sens.value = window.settings.sensitivity
+  sens.onchange = function() {
+    window.settings.sensitivity = this.value
+  }
+  sens.style.backgroundImage = 'linear-gradient(to right, ' + window.ALT_BACKGROUND + ', ' + window.ACTIVE_COLOR + ')'
+
+  // Volume
+  var volumeLabel = document.createElement('label')
+  expandedSettings.appendChild(volumeLabel)
+  volumeLabel.htmlFor = 'volume'
+  volumeLabel.innerText = 'Volume'
+
+  var volume = document.createElement('input')
+  expandedSettings.appendChild(volume)
+  volume.type = 'range'
+  volume.id = 'volume'
+  volume.min = '0'
+  volume.max = '0.24'
+  volume.step = '0.02'
+  volume.value = parseFloat(window.settings.volume)
+  volume.onchange = function() {
+    window.settings.volume = this.value
+  }
+  volume.style.backgroundImage = 'linear-gradient(to right, ' + window.ALT_BACKGROUND + ', ' + window.ACTIVE_COLOR + ')'
+
+  // Custom mechanics -- disabled for now
+  window.settings.customMechanics = false
+  /*
+  var customMechanics = createCheckbox()
+  expandedSettings.appendChild(customMechanics)
+  customMechanics.id = 'customMechanics'
+  if (window.settings.customMechanics == 'true') {
+    customMechanics.style.background = window.BORDER
+    customMechanics.checked = true
+  }
+
+  customMechanics.onpointerdown = function() {
+    this.checked = !this.checked
+    this.style.background = (this.checked ? window.BORDER : window.PAGE_BACKGROUND)
+    window.settings.customMechanics = this.checked
+    window.location.reload()
+  }
+
+  var mechLabel = document.createElement('label')
+  expandedSettings.appendChild(mechLabel)
+  mechLabel.style.marginLeft = '6px'
+  mechLabel.htmlFor = 'customMechanics'
+  mechLabel.innerText = 'Custom mechanics'
+  */
+}
+
+// Automatically solve the puzzle
+window.solvePuzzle = function() {
+  if (window.setSolveMode) window.setSolveMode(false)
+  document.getElementById('solutionViewer').style.display = 'none'
+  document.getElementById('progressBox').style.display = null
+  document.getElementById('solveAuto').innerText = 'Cancel Solving'
+  document.getElementById('solveAuto').onpointerdown = function() {
+    this.innerText = 'Cancelling...'
+    this.onpointerdown = null
+    window.setTimeout(window.cancelSolving, 0)
+  }
+
+  window.solve(window.puzzle, function(percent) {
+    document.getElementById('progressPercent').innerText = percent + '%'
+    document.getElementById('progress').style.width = percent + '%'
+  }, function(paths) {
+    document.getElementById('progressBox').style.display = 'none'
+    document.getElementById('solutionViewer').style.display = null
+    document.getElementById('progressPercent').innerText = '0%'
+    document.getElementById('progress').style.width = '0%'
+    document.getElementById('solveAuto').innerText = 'Solve (automatically)'
+    document.getElementById('solveAuto').onpointerdown = solvePuzzle
+
+    window.puzzle.autoSolved = true
+    paths = window.onSolvedPuzzle(paths)
+    window.showSolution(window.puzzle, paths, 0)
+  })
+}
+
+window.showSolution = function(puzzle, paths, num, suffix) {
+  if (suffix == null) {
+    var previousSolution = document.getElementById('previousSolution')
+    var solutionCount = document.getElementById('solutionCount')
+    var nextSolution = document.getElementById('nextSolution')
+  } else if (suffix instanceof Array) {
+    var previousSolution = document.getElementById('previousSolution-' + suffix[0])
+    var solutionCount = document.getElementById('solutionCount-' + suffix[0])
+    var nextSolution = document.getElementById('nextSolution-' + suffix[0])
+  } else {
+    var previousSolution = document.getElementById('previousSolution-' + suffix)
+    var solutionCount = document.getElementById('solutionCount-' + suffix)
+    var nextSolution = document.getElementById('nextSolution-' + suffix)
+  }
+
+  if (paths.length === 0) { // 0 paths, arrows are useless
+    solutionCount.innerText = '0 of 0'
+    previousSolution.disable()
+    nextSolution.disable()
+    return
+  }
+
+  while (num < 0) num = paths.length + num
+  while (num >= paths.length) num = num - paths.length
+
+  if (paths.length === 1) { // 1 path, arrows are useless
+    solutionCount.innerText = '1 of 1'
+    if (paths.length >= window.MAX_SOLUTIONS) solutionCount.innerText += '+'
+    previousSolution.disable()
+    nextSolution.disable()
+  } else {
+    solutionCount.innerText = (num + 1) + ' of ' + paths.length
+    if (paths.length >= window.MAX_SOLUTIONS) solutionCount.innerText += '+'
+    previousSolution.enable()
+    nextSolution.enable()
+    previousSolution.onpointerdown = function(event) {
+      if (event.shiftKey) {
+        window.showSolution(puzzle, paths, num - 10, suffix)
+      } else {
+        window.showSolution(puzzle, paths, num - 1, suffix)
+      }
+    }
+    nextSolution.onpointerdown = function(event) {
+      if (event.shiftKey) {
+        window.showSolution(puzzle, paths, num + 10, suffix)
+      } else {
+        window.showSolution(puzzle, paths, num + 1, suffix)
+      }
+    }
+  }
+
+  if (paths[num] != null) {
+    if (puzzle instanceof Array) { // Special case for multiple related panels
+      for (var i = 0; i < puzzle.length; i++) {
+        // Save the current path on the puzzle object (so that we can pass it along with publishing)
+        puzzle.path = paths[num][i]
+        // Draws the given path, and also updates the puzzle to have path annotations on it.
+        window.drawPath(puzzle[i], paths[num][i], suffix[i])
+      }
+    } else { // Default case for a single panel
+      // Save the current path on the puzzle object (so that we can pass it along with publishing)
+      puzzle.path = paths[num]
+      // Draws the given path, and also updates the puzzle to have path annotations on it.
+      window.drawPath(puzzle, paths[num], suffix)
+    }
+  }
+}
+
+window.createCheckbox = function() {
+  var checkbox = document.createElement('div')
+  checkbox.style.width = '22px'
+  checkbox.style.height = '22px'
+  checkbox.style.borderRadius = '6px'
+  checkbox.style.display = 'inline-block'
+  checkbox.style.verticalAlign = 'text-bottom'
+  checkbox.style.marginRight = '6px'
+  checkbox.style.borderWidth = '1.5px'
+  checkbox.style.borderStyle = 'solid'
+  checkbox.style.borderColor = window.BORDER
+  checkbox.style.background = window.PAGE_BACKGROUND
+  checkbox.style.color = window.TEXT_COLOR
+  return checkbox
+}
+
+// Required global variables/functions: <-- HINT: This means you're writing bad code.
+// window.puzzle
+// window.onSolvedPuzzle()
+// window.MAX_SOLUTIONS // defined by solve.js
+window.addSolveButtons = function() {
+  var parent = document.currentScript.parentElement
+
+  var solveMode = createCheckbox()
+  solveMode.id = 'solveMode'
+  parent.appendChild(solveMode)
+
+  solveMode.onpointerdown = function() {
+    this.checked = !this.checked
+    this.style.background = (this.checked ? window.BORDER : window.PAGE_BACKGROUND)
+    document.getElementById('solutionViewer').style.display = 'none'
+    if (window.setSolveMode) window.setSolveMode(this.checked)
+  }
+
+  var solveManual = document.createElement('label')
+  parent.appendChild(solveManual)
+  solveManual.id = 'solveManual'
+  solveManual.onpointerdown = function() {solveMode.onpointerdown()}
+  solveManual.innerText = 'Solve (manually)'
+  solveManual.style = 'margin-right: 8px'
+
+  var solveAuto = document.createElement('button')
+  parent.appendChild(solveAuto)
+  solveAuto.id = 'solveAuto'
+  solveAuto.innerText = 'Solve (automatically)'
+  solveAuto.onpointerdown = solvePuzzle
+  solveAuto.style = 'margin-right: 8px'
+
+  var div = document.createElement('div')
+  parent.appendChild(div)
+  div.style = 'display: inline-block; vertical-align:top'
+
+  var progressBox = document.createElement('div')
+  div.appendChild(progressBox)
+  progressBox.id = 'progressBox'
+  progressBox.style = 'display: none; width: 220px; border: 1px solid black; margin-top: 2px'
+
+  var progressPercent = document.createElement('label')
+  progressBox.appendChild(progressPercent)
+  progressPercent.id = 'progressPercent'
+  progressPercent.style = 'float: left; margin-left: 4px'
+  progressPercent.innerText = '0%'
+
+  var progress = document.createElement('div')
+  progressBox.appendChild(progress)
+  progress.id = 'progress'
+  progress.style = 'z-index: -1; height: 38px; width: 0%; background-color: #390'
+
+  var solutionViewer = document.createElement('div')
+  div.appendChild(solutionViewer)
+  solutionViewer.id = 'solutionViewer'
+  solutionViewer.style = 'display: none'
+
+  var previousSolution = document.createElement('button')
+  solutionViewer.appendChild(previousSolution)
+  previousSolution.id = 'previousSolution'
+  previousSolution.innerHTML = '&larr;'
+
+  var solutionCount = document.createElement('label')
+  solutionViewer.appendChild(solutionCount)
+  solutionCount.id = 'solutionCount'
+  solutionCount.style = 'padding: 6px'
+
+  var nextSolution = document.createElement('button')
+  solutionViewer.appendChild(nextSolution)
+  nextSolution.id = 'nextSolution'
+  nextSolution.innerHTML = '&rarr;'
+}
+
+var SECONDS_PER_LOOP = 1
+window.httpGetLoop = function(url, maxTimeout, action, onError, onSuccess) {
+  if (maxTimeout <= 0) {
+    onError()
+    return
+  }
+
+  sendHttpRequest('GET', url, SECONDS_PER_LOOP, null, function(httpCode, response) {
+    if (httpCode >= 200 && httpCode <= 299) {
+      var output = action(JSON.parse(response))
+      if (output) {
+        onSuccess(output)
+        return
+      } // Retry if action returns null
+    } // Retry on non-success HTTP codes
+
+    window.setTimeout(function() {
+      httpGetLoop(url, maxTimeout - SECONDS_PER_LOOP, action, onError, onSuccess)
+    }, 1000)
+  })
+}
+
+window.fireAndForget = function(verb, url, body) {
+  sendHttpRequest(verb, url, 600, body, function() {})
+}
+
+// Only used for errors
+var HTTP_STATUS = {
+  401: '401 unauthorized', 403: '403 forbidden', 404: '404 not found', 409: '409 conflict', 413: '413 payload too large',
+  500: '500 internal server error',
+}
+
+var etagCache = {}
+function sendHttpRequest(verb, url, timeoutSeconds, data, onResponse) {
+  currentHttpRequest = new XMLHttpRequest()
+  currentHttpRequest.onreadystatechange = function() {
+    if (this.readyState != XMLHttpRequest.DONE) return
+    etagCache[url] = this.getResponseHeader('ETag')
+    currentHttpRequest = null
+    onResponse(this.status, this.responseText || HTTP_STATUS[this.status])
+  }
+  currentHttpRequest.ontimeout = function() {
+    currentHttpRequest = null
+    onResponse(0, 'Request timed out')
+  }
+  currentHttpRequest.timeout = timeoutSeconds * 1000
+  currentHttpRequest.open(verb, url, true)
+  currentHttpRequest.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded')
+
+  var etag = etagCache[url]
+  if (etag != null) currentHttpRequest.setRequestHeader('If-None-Match', etag)
+
+  currentHttpRequest.send(data)
+}
+
+function sendFeedback(feedback) {
+  console.error('Please disregard the following CORS exception. It is expected and the request will succeed regardless.')
+}
+
+})
@@ -0,0 +1,391 @@
+namespace(function() {
+
+class RegionData {
+  constructor() {
+    this.invalidElements = []
+    this.veryInvalidElements = []
+    this.negations = []
+  }
+
+  addInvalid(elem) {
+    this.invalidElements.push(elem)
+  }
+
+  addVeryInvalid(elem) {
+    this.veryInvalidElements.push(elem)
+  }
+
+  valid() {
+    return (this.invalidElements.length === 0 && this.veryInvalidElements.length === 0)
+  }
+}
+
+// Sanity checks for data which comes from the user. Now that people have learned that /publish is an open endpoint,
+// we have to make sure they don't submit data which passes validation but is untrustworthy.
+// These checks should always pass for puzzles created by the built-in editor.
+window.validateUserData = function(puzzle, path) {
+  if (path == null) throw Error('Path cannot be null')
+
+  var sizeError = puzzle.getSizeError(puzzle.width, puzzle.height)
+  if (sizeError != null) throw Error(sizeError)
+
+  var puzzleHasStart = false
+  var puzzleHasEnd = false
+
+  if (puzzle.grid.length !== puzzle.width) throw Error('Puzzle width does not match grid size')
+  for (var x=0; x<puzzle.width; x++) {
+    if (puzzle.grid[x].length !== puzzle.height) throw Error('Puzzle height does not match grid size')
+    for (var y=0; y<puzzle.height; y++) {
+      var cell = puzzle.grid[x][y]
+      if (cell == null) continue
+
+      if (cell.start === true) {
+        puzzleHasStart = true
+        if (puzzle.symmetry != null) {
+          var symCell = puzzle.getSymmetricalCell(x, y)
+          if (symCell == null || symCell.start !== true) {
+            throw Error('Startpoint at ' + x + ' ' + y + ' does not have a symmetrical startpoint')
+          }
+        }
+      }
+      if (cell.end != null) {
+        puzzleHasEnd = true
+        if (puzzle.symmetry != null) {
+          var symCell = puzzle.getSymmetricalCell(x, y)
+          if (symCell == null || symCell.end == null || symCell.end != puzzle.getSymmetricalDir(cell.end)) {
+            throw Error('Endpoint at ' + x + ' ' + y + ' does not have a symmetrical endpoint')
+          }
+        }
+      }
+    }
+  }
+  if (!puzzleHasStart) throw Error('Puzzle does not have a startpoint')
+  if (!puzzleHasEnd) throw Error('Puzzle does not have an endpoint')
+}
+// Determines if the current grid state is solvable. Modifies the puzzle element with:
+// valid: Whether or not the puzzle is valid
+// invalidElements: Symbols which are invalid (for the purpose of negating / flashing)
+// negations: Negation pairs (for the purpose of darkening)
+window.validate = function(puzzle, quick) {
+  console.log('Validating', puzzle)
+  var puzzleData = new RegionData() // Assumed valid until we find an invalid element
+
+  var needsRegions = false
+  // These two are both used by validateRegion, so they are saved on the puzzle itself.
+  puzzle.hasNegations = false
+  puzzle.hasPolyominos = false
+
+  // Validate gap failures as an early exit.
+  for (var x=0; x<puzzle.width; x++) {
+    for (var y=0; y<puzzle.height; y++) {
+      var cell = puzzle.grid[x][y]
+      if (cell == null) continue
+      if (!needsRegions && cell.type != 'line' && cell.type != 'triangle') needsRegions = true
+      if (cell.type == 'nega') puzzle.hasNegations = true
+      if (cell.type == 'poly' || cell.type == 'ylop') puzzle.hasPolyominos = true
+      if (cell.line > window.LINE_NONE) {
+        if (cell.gap > window.GAP_NONE) {
+          console.log('Solution line goes over a gap at', x, y)
+          puzzleData.invalidElements.push({'x': x, 'y': y})
+          if (quick) return puzzleData
+        }
+        if ((cell.dot === window.DOT_BLUE && cell.line === window.LINE_YELLOW) ||
+            (cell.dot === window.DOT_YELLOW && cell.line === window.LINE_BLUE)) {
+          console.log('Incorrectly covered dot: Dot is', cell.dot, 'but line is', cell.line)
+          puzzleData.invalidElements.push({'x': x, 'y': y})
+          if (quick) return puzzleData
+        }
+      }
+    }
+  }
+
+  if (needsRegions) {
+    var regions = puzzle.getRegions()
+  } else {
+    var monoRegion = []
+    for (var x=0; x<puzzle.width; x++) {
+      for (var y=0; y<puzzle.height; y++) {
+        if (x%2 === 1 && y%2 === 1) {
+          monoRegion.push({'x': x, 'y': y})
+        } else if (puzzle.grid[x][y].line === window.LINE_NONE) {
+          monoRegion.push({'x': x, 'y': y})
+        }
+      }
+    }
+    var regions = [monoRegion]
+  }
+  console.log('Found', regions.length, 'region(s)')
+  console.debug(regions)
+
+  if (puzzle.settings.CUSTOM_MECHANICS) {
+    for (var region of regions) {
+      regionData = validateRegion(puzzle, region, quick)
+      puzzleData.negations = puzzleData.negations.concat(regionData.negations)
+      puzzleData.invalidElements = puzzleData.invalidElements.concat(regionData.invalidElements)
+      puzzleData.invalidElements = puzzleData.invalidElements.concat(regionData.veryInvalidElements)
+    }
+    // When using custom mechanics, we have to handle negations slightly differently.
+    // Negations need to be applied after all regions are validated, so that we can evaluate negations for
+    // all regions simultaneously. This is because certain custom mechanics are cross-region.
+
+    // ...
+
+  } else {
+    for (var region of regions) {
+      regionData = validateRegion(puzzle, region, quick)
+      console.log('Region valid:', regionData.valid())
+      puzzleData.negations = puzzleData.negations.concat(regionData.negations)
+      puzzleData.invalidElements = puzzleData.invalidElements.concat(regionData.invalidElements)
+      // Note: Not using veryInvalid because I don't need to do logic on these elements, just flash them.
+      puzzleData.invalidElements = puzzleData.invalidElements.concat(regionData.veryInvalidElements)
+      if (quick && !puzzleData.valid()) break
+    }
+  }
+  console.log('Puzzle has', puzzleData.invalidElements.length, 'invalid elements')
+  return puzzleData
+}
+
+// Determines whether or not a particular region is valid or not, including negation symbols.
+// If quick is true, exits after the first invalid element is found (small performance gain)
+// This function applies negations to all "very invalid elements", i.e. elements which cannot become
+// valid by another element being negated. Then, it passes off to regionCheckNegations2,
+// which attempts to apply any remaining negations to any other invalid elements.
+window.validateRegion = function(puzzle, region, quick) {
+  if (!puzzle.hasNegations) return regionCheck(puzzle, region, quick)
+
+  // Get a list of negation symbols in the grid, and set them to 'nonce'
+  var negationSymbols = []
+  for (var pos of region) {
+    var cell = puzzle.grid[pos.x][pos.y]
+    if (cell != null && cell.type === 'nega') {
+      pos.cell = cell
+      negationSymbols.push(pos)
+      puzzle.updateCell2(pos.x, pos.y, 'type', 'nonce')
+    }
+  }
+  console.debug('Found', negationSymbols.length, 'negation symbols')
+  if (negationSymbols.length === 0) {
+    // No negation symbols in this region. Note that there must be negation symbols elsewhere
+    // in the puzzle, since puzzle.hasNegations was true.
+    return regionCheck(puzzle, region, quick)
+  }
+
+  // Get a list of elements that are currently invalid (before any negations are applied)
+  // This cannot be quick, as we need a full list (for the purposes of negation).
+  var regionData = regionCheck(puzzle, region, false)
+  console.debug('Negation-less regioncheck valid:', regionData.valid())
+
+  // Set 'nonce' back to 'nega' for the negation symbols
+  for (var pos of negationSymbols) {
+    puzzle.updateCell2(pos.x, pos.y, 'type', 'nega')
+  }
+
+  var invalidElements = regionData.invalidElements
+  var veryInvalidElements = regionData.veryInvalidElements
+
+  for (var i=0; i<invalidElements.length; i++) {
+    invalidElements[i].cell = puzzle.getCell(invalidElements[i].x, invalidElements[i].y)
+  }
+  for (var i=0; i<veryInvalidElements.length; i++) {
+    veryInvalidElements[i].cell = puzzle.getCell(veryInvalidElements[i].x, veryInvalidElements[i].y)
+  }
+
+  console.debug('Forcibly negating', veryInvalidElements.length, 'symbols')
+  var baseCombination = []
+  while (negationSymbols.length > 0 && veryInvalidElements.length > 0) {
+    var source = negationSymbols.pop()
+    var target = veryInvalidElements.pop()
+    puzzle.setCell(source.x, source.y, null)
+    puzzle.setCell(target.x, target.y, null)
+    baseCombination.push({'source':source, 'target':target})
+  }
+
+  var regionData = regionCheckNegations2(puzzle, region, negationSymbols, invalidElements)
+
+  // Restore required negations
+  for (var combination of baseCombination) {
+    puzzle.setCell(combination.source.x, combination.source.y, combination.source.cell)
+    puzzle.setCell(combination.target.x, combination.target.y, combination.target.cell)
+    regionData.negations.push(combination)
+  }
+  return regionData
+}
+
+// Recursively matches negations and invalid elements from the grid. Note that this function
+// doesn't actually modify the two lists, it just iterates through them with index/index2.
+function regionCheckNegations2(puzzle, region, negationSymbols, invalidElements, index=0, index2=0) {
+  if (index2 >= negationSymbols.length) {
+    console.debug('0 negation symbols left, returning negation-less regionCheck')
+    return regionCheck(puzzle, region, false) // @Performance: We could pass quick here.
+  }
+
+  if (index >= invalidElements.length) {
+    var i = index2
+    // pair off all negation symbols, 2 at a time
+    if (puzzle.settings.NEGATIONS_CANCEL_NEGATIONS) {
+      for (; i<negationSymbols.length-1; i+=2) {
+        var source = negationSymbols[i]
+        var target = negationSymbols[i+1]
+        puzzle.setCell(source.x, source.y, null)
+        puzzle.setCell(target.x, target.y, null)
+      }
+    }
+
+    console.debug(negationSymbols.length - i, 'negation symbol(s) left over with nothing to negate')
+    for (; i<negationSymbols.length; i++) {
+      puzzle.updateCell2(negationSymbols[i].x, negationSymbols[i].y, 'type', 'nonce')
+    }
+    // Cannot be quick, as we need the full list of invalid symbols.
+    var regionData = regionCheck(puzzle, region, false)
+
+    i = index2
+    if (puzzle.settings.NEGATIONS_CANCEL_NEGATIONS) {
+      for (; i<negationSymbols.length-1; i+=2) {
+        var source = negationSymbols[i]
+        var target = negationSymbols[i+1]
+        puzzle.setCell(source.x, source.y, source.cell)
+        puzzle.setCell(target.x, target.y, target.cell)
+        regionData.negations.push({'source':source, 'target':target})
+      }
+    }
+    for (; i<negationSymbols.length; i++) {
+      puzzle.updateCell2(negationSymbols[i].x, negationSymbols[i].y, 'type', 'nega')
+      regionData.addInvalid(negationSymbols[i])
+    }
+    return regionData
+  }
+
+  var source = negationSymbols[index2++]
+  puzzle.setCell(source.x, source.y, null)
+
+  var firstRegionData = null
+  for (var i=index; i<invalidElements.length; i++) {
+    var target = invalidElements[i]
+    console.spam('Attempting negation pair', source, target)
+
+    console.group()
+    puzzle.setCell(target.x, target.y, null)
+    var regionData = regionCheckNegations2(puzzle, region, negationSymbols, invalidElements, i + 1, index2)
+    puzzle.setCell(target.x, target.y, target.cell)
+    console.groupEnd()
+
+    if (!firstRegionData) {
+      firstRegionData = regionData
+      firstRegionData.negations.push({'source':source, 'target':target})
+    }
+    if (regionData.valid()) {
+      regionData.negations.push({'source':source, 'target':target})
+      break
+    }
+  }
+
+  puzzle.setCell(source.x, source.y, source.cell)
+  // For display purposes only. The first attempt will always pair off the most negation symbols,
+  // so it's the best choice to display (if we're going to fail).
+  return (regionData.valid() ? regionData : firstRegionData)
+}
+
+// Checks if a region is valid. This does not handle negations -- we assume that there are none.
+// Note that this function needs to always ask the puzzle for the current contents of the cell,
+// since the region is only coordinate locations, and might be modified by regionCheckNegations2
+// @Performance: This is a pretty core function to the solve loop.
+function regionCheck(puzzle, region, quick) {
+  console.log('Validating region of size', region.length, region)
+  var regionData = new RegionData()
+
+  var squares = []
+  var stars = []
+  var coloredObjects = {}
+  var squareColor = null
+
+  for (var pos of region) {
+    var cell = puzzle.grid[pos.x][pos.y]
+    if (cell == null) continue
+
+    // Check for uncovered dots
+    if (cell.dot > window.DOT_NONE) {
+      console.log('Dot at', pos.x, pos.y, 'is not covered')
+      regionData.addVeryInvalid(pos)
+      if (quick) return regionData
+    }
+
+    // Check for triangles
+    if (cell.type === 'triangle') {
+      var count = 0
+      if (puzzle.getLine(pos.x - 1, pos.y) > window.LINE_NONE) count++
+      if (puzzle.getLine(pos.x + 1, pos.y) > window.LINE_NONE) count++
+      if (puzzle.getLine(pos.x, pos.y - 1) > window.LINE_NONE) count++
+      if (puzzle.getLine(pos.x, pos.y + 1) > window.LINE_NONE) count++
+      if (cell.count !== count) {
+        console.log('Triangle at grid['+pos.x+']['+pos.y+'] has', count, 'borders')
+        regionData.addVeryInvalid(pos)
+        if (quick) return regionData
+      }
+    }
+
+    // Count color-based elements
+    if (cell.color != null) {
+      var count = coloredObjects[cell.color]
+      if (count == null) {
+        count = 0
+      }
+      coloredObjects[cell.color] = count + 1
+
+      if (cell.type === 'square') {
+        squares.push(pos)
+        if (squareColor == null) {
+          squareColor = cell.color
+        } else if (squareColor != cell.color) {
+          squareColor = -1 // Signal value which indicates square color collision
+        }
+      }
+
+      if (cell.type === 'star') {
+        pos.color = cell.color
+        stars.push(pos)
+      }
+    }
+  }
+
+  if (squareColor === -1) {
+    regionData.invalidElements = regionData.invalidElements.concat(squares)
+    if (quick) return regionData
+  }
+
+  for (var star of stars) {
+    var count = coloredObjects[star.color]
+    if (count === 1) {
+      console.log('Found a', star.color, 'star in a region with 1', star.color, 'object')
+      regionData.addVeryInvalid(star)
+      if (quick) return regionData
+    } else if (count > 2) {
+      console.log('Found a', star.color, 'star in a region with', count, star.color, 'objects')
+      regionData.addInvalid(star)
+      if (quick) return regionData
+    }
+  }
+
+  if (puzzle.hasPolyominos) {
+    if (!window.polyFit(region, puzzle)) {
+      for (var pos of region) {
+        var cell = puzzle.grid[pos.x][pos.y]
+        if (cell == null) continue
+        if (cell.type === 'poly' || cell.type === 'ylop') {
+          regionData.addInvalid(pos)
+          if (quick) return regionData
+        }
+      }
+    }
+  }
+
+  if (puzzle.settings.CUSTOM_MECHANICS) {
+    window.validateBridges(puzzle, region, regionData)
+    window.validateArrows(puzzle, region, regionData)
+    window.validateSizers(puzzle, region, regionData)
+  }
+
+  console.debug('Region has', regionData.veryInvalidElements.length, 'very invalid elements')
+  console.debug('Region has', regionData.invalidElements.length, 'invalid elements')
+  return regionData
+}
+})