1 files changed, 105 insertions, 0 deletions
diff --git a/collision_system.c b/collision_system.c
new file mode 100644
index 0000000..abd5dc9
--- /dev/null
+++ b/collision_system.c
@@ -0,0 +1,105 @@
+#ifndef systems_h
+#define systems_h
+
+#include "config.h"
+#include "fx.h"
+#include "rect.h"
+#include "world.h"
+
+static void handle_bullet_vs_player(
+	World* world,
+	Entity bullet,
+	Entity player
+) {
+	const CPosition* pos;
+
+	pos = &world->positions[bullet];
+
+	destroy_entity(world, bullet);
+	new_enemy_bullet_explosion(world, pos->x, pos->y);
+}
+
+static void handle_bullet_vs_enemy(
+	World* world,
+	Entity bullet,
+	Entity enemy
+) {
+	CEnemy* e;
+
+	e = &world->enemies[enemy];
+	e->hp--;
+	destroy_entity(world, bullet);
+}
+
+static void handle(World* world, Entity a, Entity b) {
+	unsigned ab, bb;
+
+	ab = world->bitmask[a];
+	bb = world->bitmask[b];
+
+	if ((ab & ctype_enemy_bullet) && (bb & ctype_player)) {
+		handle_bullet_vs_player(world, a, b);
+		return;
+	}
+
+	if ((ab & ctype_player) && (bb & ctype_enemy_bullet)) {
+		handle_bullet_vs_player(world, b, a);
+		return;
+	}
+
+	if ((ab & ctype_player_bullet) && (bb & ctype_enemy)) {
+		handle_bullet_vs_enemy(world, a, b);
+		return;
+	}
+
+	if ((ab & ctype_enemy) && (bb & ctype_player_bullet)) {
+		handle_bullet_vs_enemy(world, b, a);
+		return;
+	}
+}
+
+void collision_system(World* world) {
+	int i, j, p0x, p0y;
+	unsigned bits;
+	const CPosition* pos0, * pos1;
+	const CCollider* col0, * col1;
+
+	for (i = 0; i < world->entity_count; i++) {
+		bits = world->bitmask[i];
+		if (
+			!(bits & ctype_collider) ||
+			!(bits & ctype_position)
+		) { continue; }
+
+		pos0 = &world->positions[i];
+		col0 = &world->colliders[i];
+		p0x = pos0->x + col0->x;
+		p0y = pos0->y + col0->y;
+
+		for (j = i + 1; j < world->entity_count; j++) {
+			bits = world->bitmask[j];
+			if (
+				!(bits & ctype_collider) ||
+				!(bits & ctype_position)
+			) { continue; }
+
+			pos1 = &world->positions[j];
+			col1 = &world->colliders[j];
+
+			if (rects_overlap2(
+				p0x,
+				p0y,
+				col0->w,
+				col0->h,
+				pos1->x + col1->x,
+				pos1->y + col1->y,
+				col1->w,
+				col1->h
+			)) {
+				handle(world, i, j);
+			}
+		}
+	}
+}
+
+#endif