Added support for desktop full screen with pillarboxing and letterboxing

and started adding some comments to the code

src/Renderer.c

@@ -15,24 +15,24 @@ struct renderer {
   SDL_Renderer *SDL_base_renderer;
 };
 
-Renderer *create_renderer() { return (Renderer *)malloc(sizeof(Renderer)); }
-
-bool init_renderer(Renderer *renderer, SDL_Window *window) {
-  if (!renderer || !window) {
-    return false;
+Renderer *create_renderer(SDL_Window *window) {
+  Renderer *renderer = (Renderer *)malloc(sizeof(Renderer));
+  if (!renderer) {
+    return NULL;
   }
 
   renderer->SDL_base_renderer = SDL_CreateRenderer(
       window, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
+  if (!(renderer->SDL_base_renderer)) {
+    destroy_renderer(&renderer);
 
-  // Technically speaking, I believe it should be possible to just return
-  // the pointer. However, to make sure that everything is clear, I am
-  // performing a test that returns true or false based on whether the
-  // pointer was initialised or not.
-  return renderer->SDL_base_renderer ? true : false;
+    return NULL;
+  }
+
+  return renderer;
 }
 
-void get_drawable_size(Renderer *renderer, int32_t *w, int32_t *h) {
+void get_render_output_size(Renderer *renderer, int32_t *w, int32_t *h) {
   SDL_GetRendererOutputSize(renderer->SDL_base_renderer, w, h);
 }
 
@@ -47,6 +47,15 @@ void render_clear(const Renderer *renderer, SDL_Color color) {
   SDL_RenderClear(renderer->SDL_base_renderer);
 }
 
+void fill_rect(const Renderer *renderer, SDL_Color color, float x, float y,
+               float w, float h) {
+  SDL_FRect dest = {x, y, w, h};
+
+  SDL_SetRenderDrawColor(renderer->SDL_base_renderer, color.r, color.g, color.b,
+                         color.a);
+  SDL_RenderFillRectF(renderer->SDL_base_renderer, &dest);
+}
+
 void render_surface(const Renderer *renderer, SDL_Surface *surface, float x,
                     float y, float w, float h) {
   SDL_Texture *texture =