Added support for desktop full screen with pillarboxing and letterboxing

and started adding some comments to the code

include/Window.h

@@ -16,12 +16,27 @@ typedef struct window_size {
   int32_t height;
 } WindowSize;
 
+typedef struct drawing_area {
+  float x;
+  float y;
+  float width;
+  float height;
+} WindowDrawingArea;
+
 typedef struct window {
+  // We need to store the defined size because the coordinates of the mouse
+  // cursor are calculated according to it. In the case of displays that support
+  // high DPI, this creates a problem, because the mouse coordinates retrieved
+  // from an SDL_Event won't work with the actual window size. By storing the
+  // defined size of the window, this allows us to convert the mouse coordinates
+  // to a ratio of the defined size, then multiply that ratio by the real size.
   WindowSize defined_size;
-  WindowSize drawable_size;
+  WindowSize real_size;
+  WindowDrawingArea drawing_area;
   Renderer *renderer;
   SDL_Window *SDL_base_window;
   SDL_Color background_color;
+  bool full_screen;
 } Window;
 
 bool init_window(Window *wnd, const char *title, WindowSize size,