streamline collision detection

combat.c

@@ -109,84 +109,94 @@ void populateTargetCollision(struct CompiledSpriteRender *sprite) {
   collisionDetection.targetEY = bounds.bottom;
 }
 
-void handleRabbitToEnemyCollisions(
+// We are hardcoding a 2x2 grid on the screen as our collision partitioning
+// scheme.
+int rabbitBulletGrid[4][RABBIT_BULLET_LIMIT];
+int enemyGrid[4][ENEMY_MAX_COUNT];
+int rabbitGrid[4];
+int rabbitBulletGridIndex[4], enemyGridIndex[4];
+
+int gridPosition[4];
+
+#define CALCULATE_GRID_POS(x,y) ((x / COLLISION_GRID_SIZE) + (y / COLLISION_GRID_SIZE) * 2)
+
+void determineGridPositionsForSprite(struct CompiledSpriteRender *sprite) {
+  int i;
+
+  getSpriteBounds(sprite, &bounds);
+
+  for (i = 0; i < 4; ++i) {
+    gridPosition[i] = 0;
+  }
+
+  gridPosition[CALCULATE_GRID_POS(bounds.left, bounds.top)] = 1;
+  gridPosition[CALCULATE_GRID_POS(bounds.right, bounds.top)] = 1;
+  gridPosition[CALCULATE_GRID_POS(bounds.left, bounds.bottom)] = 1;
+  gridPosition[CALCULATE_GRID_POS(bounds.right, bounds.bottom)] = 1;
+}
+
+void buildCollisionGrids(
+  struct BulletPosition rabbitBulletPosition[],
   struct RabbitPosition *rabbitPosition,
   struct EnemyPosition enemyPosition[]
 ) {
-  int enemyIdx;
+  int grid, i;
+
+  for (grid = 0; grid < 4; ++grid) {
+    rabbitBulletGridIndex[grid] = 0;
+    enemyGridIndex[grid] = 0;
+  }
 
-  // to start: brute force items
-  // possible performance improvements:
-  // * grid partitioning
   rabbit.x = rabbitPosition->rabbitPosition[0];
   rabbit.y = rabbitPosition->rabbitPosition[1];
-  populateSourceCollision(&rabbit);
+  determineGridPositionsForSprite(&rabbit);
 
-  for (enemyIdx = 0; enemyIdx < ENEMY_MAX_COUNT; ++enemyIdx) {
+  for (grid = 0; grid < 4; ++grid) {
-    if (!enemyPosition[enemyIdx].isActive) continue;
+    rabbitGrid[grid] = gridPosition[grid];
-    if (enemyPosition[enemyIdx].willBeInactive) continue;
+  }
 
-    enemy.x = enemyPosition[enemyIdx].enemyPosition[0];
+  for (i = 0; i < RABBIT_BULLET_LIMIT; ++i) {
-    enemy.y = enemyPosition[enemyIdx].enemyPosition[1];
+    if (!rabbitBulletPosition[i].isActive) continue;
-    populateTargetCollision(&enemy);
+    if (rabbitBulletPosition[i].willBeInactive) continue;
 
-    if (isCollision()) {
+    bullet.x = rabbitBulletPosition[i].x;
-      enemyPosition[enemyIdx].willBeInactive = 1;
+    bullet.y = rabbitBulletPosition[i].y;
+    determineGridPositionsForSprite(&bullet);
+
+    for (grid = 0; grid < 4; ++grid) {
+      if (gridPosition[grid]) {
+        rabbitBulletGrid[grid][rabbitBulletGridIndex[grid]++] = i;
+      }
+    }
+  }
+
+  for (i = 0; i < ENEMY_MAX_COUNT; ++i) {
+    if (!enemyPosition[i].isActive) continue;
+    if (enemyPosition[i].willBeInactive) continue;
+
+    enemy.x = enemyPosition[i].enemyPosition[0];
+    enemy.y = enemyPosition[i].enemyPosition[1];
+    determineGridPositionsForSprite(&enemy);
+
+    for (grid = 0; grid < 4; ++grid) {
+      if (gridPosition[grid]) {
+        enemyGrid[grid][enemyGridIndex[grid]++] = i;
+      }
     }
   }
 }
 
-int rabbitBulletGrid[4][RABBIT_BULLET_LIMIT];
-int enemyGrid[4][ENEMY_MAX_COUNT];
-
 void handleRabbitBulletToEnemyCollisions(
   struct BulletPosition rabbitBulletPosition[],
   struct EnemyPosition enemyPosition[]
 ) {
   int bulletIdx, enemyIdx, grid;
   int resolvedBulletIdx, resolvedEnemyIdx;
-  int rabbitGridIndex[4], enemyGridIndex[4];
-
-  char buffer[30];
-
-  for (grid = 0; grid < 4; ++grid) {
-    rabbitGridIndex[grid] = 0;
-  }
-
-  for (bulletIdx = 0; bulletIdx < RABBIT_BULLET_LIMIT; ++bulletIdx) {
-    if (!rabbitBulletPosition[bulletIdx].isActive) continue;
-    if (rabbitBulletPosition[bulletIdx].willBeInactive) continue;
-
-    grid = (
-      rabbitBulletPosition[bulletIdx].x / (TILE_SIZE * 5)
-    ) + (
-      (rabbitBulletPosition[bulletIdx].y / (TILE_SIZE * 5)) * 2
-    );
-
-    rabbitBulletGrid[grid][rabbitGridIndex[grid]++] = bulletIdx;
-  }
-
-  for (grid = 0; grid < 4; ++grid) {
-    enemyGridIndex[grid] = 0;
-  }
-
-  for (enemyIdx = 0; enemyIdx < ENEMY_MAX_COUNT; ++enemyIdx) {
-    if (!enemyPosition[enemyIdx].isActive) continue;
-    if (enemyPosition[enemyIdx].willBeInactive) continue;
-
-    grid = (
-      enemyPosition[enemyIdx].enemyPosition[0] / (TILE_SIZE * 5)
-    ) + (
-      (enemyPosition[enemyIdx].enemyPosition[1] / (TILE_SIZE * 5)) * 2
-    );
-
-    enemyGrid[grid][enemyGridIndex[grid]++] = enemyIdx;
-  }
 
   for (grid = 0; grid < 4; ++grid) {
     if (enemyGridIndex[grid] == 0) continue;
 
-    for (bulletIdx = 0; bulletIdx < rabbitGridIndex[grid]; ++bulletIdx) {
+    for (bulletIdx = 0; bulletIdx < rabbitBulletGridIndex[grid]; ++bulletIdx) {
       resolvedBulletIdx = rabbitBulletGrid[grid][bulletIdx];
 
       if (!rabbitBulletPosition[resolvedBulletIdx].isActive) continue;
@@ -216,3 +226,37 @@ void handleRabbitBulletToEnemyCollisions(
   }
 }
 
+void handleRabbitToEnemyCollisions(
+  struct RabbitPosition *rabbitPosition,
+  struct EnemyPosition enemyPosition[]
+) {
+  int enemyIdx, grid, resolvedEnemyIdx;
+
+  // to start: brute force items
+  // possible performance improvements:
+  // * grid partitioning
+  rabbit.x = rabbitPosition->rabbitPosition[0];
+  rabbit.y = rabbitPosition->rabbitPosition[1];
+  populateSourceCollision(&rabbit);
+
+  for (grid = 0; grid < 4; ++grid) {
+    if (!rabbitGrid[grid]) continue;
+    if (enemyGridIndex[grid] == 0) continue;
+
+    for (enemyIdx = 0; enemyIdx < enemyGridIndex[grid]; ++enemyIdx) {
+      resolvedEnemyIdx = enemyGrid[grid][enemyIdx];
+
+      if (!enemyPosition[resolvedEnemyIdx].isActive) continue;
+      if (enemyPosition[resolvedEnemyIdx].willBeInactive) continue;
+
+      enemy.x = enemyPosition[resolvedEnemyIdx].enemyPosition[0];
+      enemy.y = enemyPosition[resolvedEnemyIdx].enemyPosition[1];
+      populateTargetCollision(&enemy);
+
+      if (isCollision()) {
+        enemyPosition[resolvedEnemyIdx].willBeInactive = 1;
+      }
+    }
+  }
+}
+

combat.h

@@ -18,3 +18,9 @@ void handleRabbitToEnemyCollisions(
   struct RabbitPosition*,
   struct EnemyPosition[]
 );
+
+void buildCollisionGrids(
+  struct BulletPosition rabbitBulletPosition[],
+  struct RabbitPosition *rabbitPosition,
+  struct EnemyPosition enemyPosition[]
+);

const.h

@@ -1,6 +1,7 @@
 #define TILE_SIZE (20)
 #define ARENA_WIDTH_TILES (10)
 #define ARENA_HEIGHT_TILES (10)
+#define COLLISION_GRID_SIZE (ARENA_WIDTH_TILES / 2 * TILE_SIZE)
 
 #define MOUSE_DISTANCE (32)
 

game.c

@@ -286,6 +286,12 @@ void handleCombat() {
     &rabbitWeaponry
   );
 
+  buildCollisionGrids(
+    rabbitBulletPosition,
+    &rabbitPosition,
+    enemyPosition
+  );
+
   handleRabbitToEnemyCollisions(
     &rabbitPosition,
     enemyPosition
@@ -337,10 +343,10 @@ int main(void) {
 
     handleMovement();
     handleRedraw();
+    handleCombat();
 
     waitStartVbl();
     copyDrawBufferToDisplay();
-    handleCombat();
     waitEndVbl();
 
     if (keyboardKeydownState.KEY_ESC) { keepRunning = 0; }