Added support for desktop full screen with pillarboxing and letterboxing

and started adding some comments to the code

include/Renderer.h

@@ -14,16 +14,41 @@ extern "C" {
 
 typedef struct renderer Renderer;
 
-Renderer *create_renderer();
-bool init_renderer(Renderer *renderer, SDL_Window *window);
-void get_drawable_size(Renderer *renderer, int32_t *w, int32_t *h);
+/**
+ * Attempts to allocate a Renderer object on the heap.
+ *
+ * Returns the pointer to the object when it succeeds, or NULL if it fails.
+ */
+Renderer *create_renderer(SDL_Window *window);
+
+/**
+ * Returns the valid drawable area that the renderer can use.
+ *
+ * Useful when rendering on screens that support high DPI since the drawable
+ * area is usually bigger than the user-defined size.
+ */
+void get_render_output_size(Renderer *renderer, int32_t *w, int32_t *h);
+
+/**
+ * Attempts to load an SDL_Texture from a file path.
+ *
+ * Returns a pointer to the object if it succeeds or NULL when it fails.
+ */
 SDL_Texture *load_texture(const Renderer *renderer, const char *path);
+
 void render_clear(const Renderer *renderer, SDL_Color color);
+void fill_rect(const Renderer *renderer, SDL_Color color, float x, float y,
+               float w, float h);
 void render_surface(const Renderer *renderer, SDL_Surface *surface, float x,
                     float y, float w, float h);
 void render_texture(const Renderer *renderer, SDL_Texture *texture, float x,
                     float y, float w, float h);
 void swap_buffers(const Renderer *renderer);
+
+/**
+ * Frees the memory allocated to the Renderer object and performs the
+ * necessary cleanup.
+ */
 void destroy_renderer(Renderer **renderer);
 
 #ifdef __cplusplus