Fixed orbit

mechanics.c

@@ -73,25 +73,23 @@ void collide_rigid(mass_body_t *a, float restitution) {
 }
 
 void mechanics(universe_t *uni) {
-  mass_body_t body_1;
-  mass_body_t body_2;
-  Vector2 collision;
-  Vector2 scaled_speed;
+  // Advance every body to the same simulated time before checking contacts.
   for (unsigned int i = 0; i < uni->num_bodies; i++) {
-    body_1 = uni->bodies[i];
-    scaled_speed = vec2_scale(body_1.speed, 1.0 / simx);
-    body_1.position = vec2_sum(body_1.position, scaled_speed);
-    if (i < uni->num_bodies - 1) {
-      for (unsigned int y = i + 1; y < uni->num_bodies; y++) {
-        body_2 = uni->bodies[y];
-        collision = body_collision(&body_1, &body_2);
-        if (!vec2_is_null(collision)) {
-          collide(&body_1, &body_2, collision, 0.99);
-        }
-        uni->bodies[y] = body_2;
+    mass_body_t *body = &uni->bodies[i];
+    body->position = vec2_sum(body->position,
+                             vec2_scale(body->speed, PHYSICS_TIMESTEP));
+  }
+  for (unsigned int i = 0; i < uni->num_bodies; i++) {
+    mass_body_t *body_1 = &uni->bodies[i];
+    for (unsigned int y = i + 1; y < uni->num_bodies; y++) {
+      mass_body_t *body_2 = &uni->bodies[y];
+      Vector2 collision = body_collision(body_1, body_2);
+      if (!vec2_is_null(collision)) {
+        collide(body_1, body_2, collision, 0.99);
       }
     }
-    collide_rigid(&body_1, 1.1);
-    uni->bodies[i] = body_1;
+    if (WALL_COLLISIONS) {
+      collide_rigid(body_1, 1.0f);
+    }
   }
 }