optimize case of sequential shared radius circle drawing by reusing the geometry by just offsetting it

apps/demos/platformer/player.c

@@ -255,6 +255,10 @@ static void drawdef(Player *player) {
     draw_circle((Vec2) { 256, 128 },
                 24,
                 (Color) { 255, 0, 0, 255 });
+
+    draw_circle((Vec2) { 304, 128 },
+                24,
+                (Color) { 255, 0, 0, 255 });
 }
 
 

src/rendering/twn_gl_15_rendering.c

@@ -911,12 +911,26 @@ static void load_cubemap_side(const char *path, GLenum target) {
 
 void render_circle(const CirclePrimitive *circle) {
     static Vec2 vertices[CIRCLE_VERTICES_MAX];
-    int num_vertices = MIN((int)circle->radius, CIRCLE_VERTICES_MAX);
+    static int prev_num_vertices = 0;
+    static Vec2 prev_position = {0};
 
-    create_circle_geometry(circle->position,
+    int const num_vertices = MIN((int)circle->radius, CIRCLE_VERTICES_MAX);
-                           circle->radius,
+
-                           num_vertices,
+    if (prev_num_vertices != num_vertices) {
-                           vertices);
+        create_circle_geometry(circle->position,
+                               circle->radius,
+                               num_vertices,
+                               vertices);
+        prev_num_vertices = num_vertices;
+        prev_position = circle->position;
+    } else {
+        /* reuse the data, but offset it by difference with previously generated position */
+        /* no evil cos sin ops this way, if radius is shared in sequential calls */
+        Vec2 const d = { prev_position.x - circle->position.x, prev_position.y - circle->position.y };
+        for (int i = 0; i < num_vertices; ++i)
+            vertices[i] = (Vec2){ vertices[i].x - d.x, vertices[i].y - d.y };
+        prev_position = circle->position;
+    }
 
     VertexBuffer buffer = get_scratch_vertex_array();
     specify_vertex_buffer(buffer, vertices, sizeof (Vec2) * num_vertices);