SDL_SetEventFilter- Sets up a filter to process all events before they are
posted to the event queue.
void SDL_SetEventFilter(SDL_EventFilter filter);
This function sets up a filter to process all events before they are posted to
the event queue. This is a very powerful and flexible feature. The filter is
typedef int (*SDL_EventFilter)(const SDL_Event *event);
If the filter returns 1, then the event will be added to the internal queue. If
it returns 0, then the event will be dropped from the queue. This allows
selective filtering of dynamically.
There is one caveat when dealing with the SDL_QUITEVENT event type. The event
filter is only called when the window manager desires to close the application
window. If the event filter returns 1, then the window will be closed, otherwise
the window will remain open if possible. If the quit event is generated by an
interrupt signal, it will bypass the internal queue and be delivered to the
application at the next event poll.
Events pushed onto the queue with SDL_PushEvent or SDL_PeepEvents do not get
passed through the event filter.
Be Careful! The event filter function may run in a different thread so be
careful what you do within it.
SDL_Event, SDL_GetEventFilter, SDL_PushEvent