use static, fixed arrays for circle geometry data instead of allocating for each one

src/rendering/twn_circles.c

@@ -22,18 +22,14 @@ void draw_circle(Vec2 position, float radius, Color color) {
     arrput(ctx.render_queue_2d, primitive);
 }
 
-/* TODO: caching and reuse scheme */
-/* vertices_out and indices_out MUST BE FREED */
+
 void create_circle_geometry(Vec2 position,
                             Color color,
                             float radius,
                             size_t num_vertices,
-                            SDL_Vertex **vertices_out,
-                            int **indices_out)
+                            SDL_Vertex vertices[],
+                            int indices[])
 {
-    SDL_Vertex *vertices = cmalloc(sizeof *vertices * (num_vertices + 1));
-    int *indices = cmalloc(sizeof *indices * (num_vertices * 3));
-
     /* the angle (in radians) to rotate by on each iteration */
     float seg_rotation_angle = (360.0f / (float)num_vertices) * ((float)M_PI / 180);
 
@@ -82,7 +78,4 @@ void create_circle_geometry(Vec2 position,
             index = num_vertices;
         indices[triangle_offset + 2] = (int)index;
     }
-
-    *vertices_out = vertices;
-    *indices_out = indices;
 }