Fix major incorrect usage of mrb class definitions causing segfaults

include/window/window.h

@@ -14,6 +14,11 @@ struct Font {
   bool pixel_art;
 };
 
+struct Text {
+  SDL_Texture *texture;
+  Vec2<float> size;
+};
+
 struct Event {
   enum Type {
     NONE,
@@ -57,8 +62,11 @@ struct Animation {
   std::vector<int> frames;
   float frame_rate;
   bool loop;
+  int reference_count = 0;
 };
 
+inline Pool<Animation> animation_pool;
+
 struct Window {
 public:
   // title can be free'd by the caller after the window is created, as it's copied internally.
@@ -70,10 +78,12 @@ public:
 
   // Rendering functions
   int load_image(const char *path, float alpha = 1.0f, bool pixel_art = false);
+  void use_image(int image_id);
   void unload_image(int image_id);
   Vec2<float> get_image_size(int image_id);
 
   int load_font(const char *path, int font_size, bool bold = false, bool italic = false, bool underline = false, bool pixel_art = false);
+  void use_font(int font_id);
   void unload_font(int font_id);
 
   // text is copied internally, so it can be free'd by the caller after the text is created.
@@ -135,7 +145,7 @@ private:
   Pool<Font> font_pool;
 
   // Text pool
-  Pool<SDL_Texture *> text_pool;
+  Pool<Text> text_pool;
 
   struct RenderInstruction {
     enum Type {