Added sliding around solid tiles

#3

5 files changed, 78 insertions, 3 deletions

@@ -153,7 +153,7 @@ void CharacterSystem::tick(double dt) {
         pLoc += (unitVecInDirection(sprite.movementDir) * speed);
 
         // Check collision.
-        CollisionResult collision = game_.getSystem<TransformSystem>().checkCollision(spriteId, sprite.loc, pLoc, sprite.movementDir);
+        CollisionResult collision = game_.getSystem<TransformSystem>().checkCollision(spriteId, sprite.loc, pLoc, sprite.movementDir, CheckCollisionOptions::AllowSliding);
 
         if (!(collision.blocked && sprite.clipping)) {
           pLoc = collision.adjustedLoc;
@@ -42,6 +42,7 @@ void loop(Renderer& renderer, std::mt19937& rng) {
   game.getSprite(lucasSprite).player = true;
   game.getSprite(lucasSprite).controllable = true;
   game.getSprite(lucasSprite).persistent = true;
+  game.getSprite(lucasSprite).sliding = true;
   game.getSystem<CharacterSystem>().initSprite(lucasSprite, LUCAS_MOVEMENT_SPEED);
   game.getSystem<CameraSystem>().setFollowingSprite(lucasSprite);
   game.getSystem<CameraSystem>().unlockCamera();
@@ -83,6 +83,7 @@ public:
   std::string walkthroughScript;
   std::string bumpPlayerScript;
   std::string enclosureZone;
+  bool sliding = false;
 
   // Animation (internals)
   bool isAnimated = false;
@@ -2,6 +2,10 @@
 #include "game.h"
 #include "map.h"
 
+bool checkCollisionOptionsContains(CheckCollisionOptions options, CheckCollisionOptions value) {
+  return (static_cast<int>(options) & static_cast<int>(value)) != 0;
+}
+
 void TransformSystem::initSprite(int spriteId, vec2i loc, SpriteLayer layer) {
   Sprite& sprite = game_.getSprite(spriteId);
   sprite.loc = loc;
@@ -47,7 +51,7 @@ void TransformSystem::moveSprite(int spriteId, vec2i newLoc) {
   }
 }
 
-CollisionResult TransformSystem::checkCollision(int spriteId, vec2i curLoc, vec2i newLoc, Direction dir) {
+CollisionResult TransformSystem::checkCollision(int spriteId, vec2i curLoc, vec2i newLoc, Direction dir, CheckCollisionOptions options) {
   CollisionResult result;
 
   Sprite& sprite = game_.getSprite(spriteId);
@@ -87,6 +91,22 @@ CollisionResult TransformSystem::checkCollision(int spriteId, vec2i curLoc, vec2
           break;
         }
       }
+
+      if (checkCollisionOptionsContains(options, CheckCollisionOptions::AllowSliding) &&
+          sprite.sliding &&
+          dir == Direction::right &&
+          horizBlocked &&
+          oldTileUL.y() != oldTileDR.y()) {
+        // If sliding is enabled for this sprite, check if we can slide
+        // either perpendicular direction. Because sliding can only happen
+        // if we were moving in a cardinal direction, we can use tail
+        // recursion and exit early.
+        if (!map.isBlocked(oldTileDR.x()+1, oldTileUL.y())) {
+          return checkCollision(spriteId, curLoc, curLoc - vec2i{0,1} * sprite.movementSpeed, Direction::up);
+        } else if (!map.isBlocked(oldTileDR.x()+1, oldTileDR.y())) {
+          return checkCollision(spriteId, curLoc, curLoc + vec2i{0,1} * sprite.movementSpeed, Direction::down);
+        }
+      }
     }
 
     if (!horizBlocked && enclosureZone) {
@@ -128,6 +148,22 @@ CollisionResult TransformSystem::checkCollision(int spriteId, vec2i curLoc, vec2
           break;
         }
       }
+
+      if (checkCollisionOptionsContains(options, CheckCollisionOptions::AllowSliding) &&
+          sprite.sliding &&
+          dir == Direction::left &&
+          horizBlocked &&
+          oldTileUL.y() != oldTileDR.y()) {
+        // If sliding is enabled for this sprite, check if we can slide
+        // either perpendicular direction. Because sliding can only happen
+        // if we were moving in a cardinal direction, we can use tail
+        // recursion and exit early.
+        if (!map.isBlocked(oldTileUL.x()-1, oldTileUL.y())) {
+          return checkCollision(spriteId, curLoc, curLoc - vec2i{0,1} * sprite.movementSpeed, Direction::up);
+        } else if (!map.isBlocked(oldTileUL.x()-1, oldTileDR.y())) {
+          return checkCollision(spriteId, curLoc, curLoc + vec2i{0,1} * sprite.movementSpeed, Direction::down);
+        }
+      }
     }
 
     if (!horizBlocked && enclosureZone) {
@@ -191,6 +227,22 @@ CollisionResult TransformSystem::checkCollision(int spriteId, vec2i curLoc, vec2
           break;
         }
       }
+
+      if (checkCollisionOptionsContains(options, CheckCollisionOptions::AllowSliding) &&
+          sprite.sliding &&
+          dir == Direction::down &&
+          vertBlocked &&
+          oldTileUL.x() != oldTileDR.x()) {
+        // If sliding is enabled for this sprite, check if we can slide
+        // either perpendicular direction. Because sliding can only happen
+        // if we were moving in a cardinal direction, we can use tail
+        // recursion and exit early.
+        if (!map.isBlocked(oldTileUL.x(), oldTileDR.y()+1)) {
+          return checkCollision(spriteId, curLoc, curLoc - vec2i{1,0} * sprite.movementSpeed, Direction::left);
+        } else if (!map.isBlocked(oldTileDR.x(), oldTileDR.y()+1)) {
+          return checkCollision(spriteId, curLoc, curLoc + vec2i{1,0} * sprite.movementSpeed, Direction::right);
+        }
+      }
     }
 
     if (!vertBlocked && enclosureZone) {
@@ -232,6 +284,22 @@ CollisionResult TransformSystem::checkCollision(int spriteId, vec2i curLoc, vec2
           break;
         }
       }
+
+      if (checkCollisionOptionsContains(options, CheckCollisionOptions::AllowSliding) &&
+          sprite.sliding &&
+          dir == Direction::up &&
+          vertBlocked &&
+          oldTileUL.x() != oldTileDR.x()) {
+        // If sliding is enabled for this sprite, check if we can slide
+        // either perpendicular direction. Because sliding can only happen
+        // if we were moving in a cardinal direction, we can use tail
+        // recursion and exit early.
+        if (!map.isBlocked(oldTileUL.x(), oldTileUL.y()-1)) {
+          return checkCollision(spriteId, curLoc, curLoc - vec2i{1,0} * sprite.movementSpeed, Direction::left);
+        } else if (!map.isBlocked(oldTileDR.x(), oldTileUL.y()-1)) {
+          return checkCollision(spriteId, curLoc, curLoc + vec2i{1,0} * sprite.movementSpeed, Direction::right);
+        }
+      }
     }
 
     if (!vertBlocked && enclosureZone) {
@@ -21,6 +21,11 @@ struct CollisionResult {
   vec2i adjustedLoc;
 };
 
+enum class CheckCollisionOptions {
+  None         = 0,
+  AllowSliding = 1 << 0
+};
+
 class TransformSystem : public System {
 public:
 
@@ -42,7 +47,7 @@ public:
     });
   }
 
-  CollisionResult checkCollision(int spriteId, vec2i curLoc, vec2i newLoc, Direction dir);
+  CollisionResult checkCollision(int spriteId, vec2i curLoc, vec2i newLoc, Direction dir, CheckCollisionOptions options = CheckCollisionOptions::None);
 
   CharacterMedium getMediumAtPosition(int spriteId, vec2i newLoc);