Refactor into more modular architecture

collisions.c

@@ -0,0 +1,87 @@
+#include "collisions.h"
+
+#include "entity.h"
+
+#include <assert.h>
+#include <string.h>
+
+typedef struct {
+	bool valid;
+	unsigned component_id;
+	float r;
+	unsigned priority;
+	collision_cb_t cb;
+} entry_t;
+
+static unsigned max;
+static entry_t entries[MAX_ENTITIES];
+
+static void update(unsigned new_entity_id, void *ref)
+{
+	entry_t *old_e = (entry_t *)ref;
+	entry_t *new_e = entries + new_entity_id;
+	memcpy(new_e, old_e, sizeof(entry_t));
+	old_e->valid = false;
+	entity_update_component(new_entity_id, new_e->component_id, new_e);
+}
+
+static void remove(void *ref)
+{
+	entry_t *e = (entry_t *)ref;
+	e->valid = false;
+}
+
+void collisions_init()
+{
+	max = 0;
+}
+
+void collisions_update()
+{
+	for (unsigned i = 0; i < max; ++i) {
+		if (!entries[i].valid)
+			continue;
+
+		for (unsigned j = i + 1; j < max; ++j) {
+			if (!entries[j].valid)
+				continue;
+
+			const physics_sep_t sep = physics_separation(i, j);
+			if (sep.dist > entries[i].r + entries[j].r)
+				continue;
+			if (sep.va - sep.vb <= 0)
+				continue;
+
+			if (entries[i].priority >= entries[j].priority) {
+				entries[i].cb(i, j, sep);
+			} else {
+				const physics_sep_t flip_sep = {
+					.dist = sep.dist,
+					.norm = vec2_scale(sep.norm, -1),
+					.va = -sep.vb,
+					.vb = -sep.va,
+				};
+				entries[j].cb(j, i, flip_sep);
+			}
+		}
+	}
+}
+
+void collisions_add(
+    unsigned entity, float radius, unsigned priority, collision_cb_t cb)
+{
+	assert(entity < MAX_ENTITIES);
+	if (entity >= max)
+		max = entity + 1;
+	else
+		assert(!entries[entity].valid);
+
+	entry_t *entry = entries + entity;
+	entry->valid = true;
+	entry->component_id
+	    = entity_add_component(entity, update, remove, entry);
+
+	entry->r = radius;
+	entry->priority = priority;
+	entry->cb = cb;
+}