void app_keyboard(int key, bool pressed);
void app_mouse_button(int bn, bool pressed, int x, int y);
void app_mouse_motion(int x, int y);
+void app_mouse_delta(int dx, int dy);
// the following functions are implemented by the window system backend
void app_resize(int x, int y);
void app_fullscreen(bool fs);
+void app_toggle_fullscreen();
+bool app_is_fullscreen();
+void app_grab_mouse(bool grab);
+void app_toggle_grab_mouse();
+bool app_is_mouse_grabbed();
void app_quit();
void app_redraw();
void app_swap_buffers();