rendering: use sprite batching techniques for rect primitives, unite their render path

src/rendering/twn_sprites.c

@@ -60,15 +60,18 @@ void draw_sprite_args(const DrawSpriteArgs args) {
 }
 
 
-struct SpriteBatch collect_sprite_batch(const Primitive2D primitives[], size_t len) {
-    /* assumes that first primitive is already a sprite */
+struct QuadBatch collect_sprite_batch(const Primitive2D primitives[], size_t len) {
+    SDL_assert(primitives[0].type == PRIMITIVE_2D_SPRITE);
+    SDL_assert(primitives && len != 0);
+
     const uint16_t texture_key_id = primitives[0].sprite.texture_key.id;
     const int atlas_id = textures_get_atlas_id(&ctx.texture_cache, primitives[0].sprite.texture_key);
 
-    struct SpriteBatch batch = {
+    struct QuadBatch batch = {
         .mode = textures_get_mode(&ctx.texture_cache, primitives[0].sprite.texture_key),
         .constant_colored = true,
         .repeat = primitives[0].sprite.repeat,
+        .textured = true,
     };
 
     const uint32_t uniform_color = *(const uint32_t *)&primitives[0].sprite.color;
@@ -116,9 +119,12 @@ struct SpriteBatch collect_sprite_batch(const Primitive2D primitives[], size_t l
 
 
 /* assumes that orthogonal matrix setup is done already */
-void render_sprites(const Primitive2D primitives[],
-                    const struct SpriteBatch batch)
+void render_sprite_batch(const Primitive2D primitives[],
+                         const struct QuadBatch batch)
 {
+    SDL_assert(primitives && batch.size != 0);
+    SDL_assert(primitives[0].type == PRIMITIVE_2D_SPRITE);
+
     /* single vertex array is used for every batch with NULL glBufferData() trick at the end */
     static VertexBuffer vertex_array = 0;
     if (vertex_array == 0)
@@ -131,10 +137,10 @@ void render_sprites(const Primitive2D primitives[],
 
     /* vertex population over a vertex buffer builder interface */
     {
-        VertexBufferBuilder payload = build_vertex_buffer(vertex_array, get_sprite_payload_size(batch) * batch.size);
+        VertexBufferBuilder payload = build_vertex_buffer(vertex_array, get_quad_payload_size(batch) * batch.size);
 
         for (size_t i = 0; i < batch.size; ++i) {
-            /* render opaques front to back */
+            /* render opaques front to back, to gain benefit of an early z rejection */
             const size_t cur = batch.mode == TEXTURE_MODE_GHOSTLY ? i : batch.size - i - 1;
             const SpritePrimitive sprite = primitives[cur].sprite;
 
@@ -233,9 +239,9 @@ void render_sprites(const Primitive2D primitives[],
                 v3 = (Vec2){ c.x + t.x * +h.x - t.y * -h.y, c.y + t.y * +h.x + t.x * -h.y };
             }
 
-            push_sprite_payload_to_vertex_buffer_builder(batch, &payload, v0, v1, v2, v3, uv0, uv1, uv2, uv3, sprite.color);
+            push_quad_payload_to_vertex_buffer_builder(batch, &payload, v0, v1, v2, v3, uv0, uv1, uv2, uv3, sprite.color);
         }
     }
 
-    finally_render_sprites(primitives, batch, vertex_array);
+    finally_render_quads(primitives, batch, vertex_array);
 }