The callback that is invoked every time glview is about to display a frame.
#include <glview/glview.h>
typedef void(* frame_callback)(void *callback_data);
The frame_callback is invoked within the glview_loop() function every time the application is expected to draw a single frame. By default this occurs 60 times a second.
The callback will not be invoked if the app is no longer expected to draw a frame. This can occur if the app has been minimized, or is hidden in some way (by the user's action, or on idle timeout). An app can still draw during this time (for example, to show a pause screen) by calling the glview_display_once() function.