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

src/rendering/twn_quads.c

@@ -0,0 +1,30 @@
+#include "twn_draw_c.h"
+
+#include <stddef.h>
+
+
+struct QuadBatch collect_quad_batch(const Primitive2D primitives[], size_t len) {
+    if (primitives[0].type == PRIMITIVE_2D_SPRITE)
+        return collect_sprite_batch(primitives, len);
+    else if (primitives[0].type == PRIMITIVE_2D_RECT)
+        return collect_rect_batch(primitives, len);
+    else
+        SDL_assert(false);
+
+    return (struct QuadBatch){0};
+}
+
+
+/* assumes that orthogonal matrix setup is done already */
+void render_quad_batch(const Primitive2D primitives[],
+                       const struct QuadBatch batch)
+{
+    if (primitives[0].type == PRIMITIVE_2D_SPRITE)
+        render_sprite_batch(primitives, batch);
+    else if (primitives[0].type == PRIMITIVE_2D_RECT)
+        render_rect_batch(primitives, batch);
+    else
+        SDL_assert(false);
+
+    return (struct QuadBatch){0};
+}