extern int win_width, win_height;
extern float win_aspect;
extern long time_msec;
+extern double time_sec;
extern Mat4 view_matrix;
void app_mouse_motion(int x, int y);
// the following functions are implemented by the window system backend
+void app_resize(int x, int y);
+void app_fullscreen(bool fs);
void app_quit();
void app_redraw();
void app_swap_buffers();