Add a callback to be triggered when an event is added to the event queue.
filter will be called when an event happens, and its return value is
ignored.
**WARNING**: Be very careful of what you do in the event filter function,
as it may run in a different thread!
If the quit event is generated by a signal (e.g. SIGINT), it will bypass
the internal queue and be delivered to the watch callback immediately, and
arrive at the next event poll.
Note: the callback is called for events posted by the user through
SDL_PushEvent(), but not for disabled events, nor for events by a filter
callback set with SDL_SetEventFilter(), nor for events posted by the user
through SDL_PeepEvents().
\param filter an SDL_EventFilter function to call when an event happens.
\param userdata a pointer that is passed to filter.
\returns true on success or false on failure; call SDL_GetError() for more
information.
\threadsafety It is safe to call this function from any thread.
\since This function is available since SDL 3.2.0.
Add a callback to be triggered when an event is added to the event queue.
filter will be called when an event happens, and its return value is ignored.
**WARNING**: Be very careful of what you do in the event filter function, as it may run in a different thread!
If the quit event is generated by a signal (e.g. SIGINT), it will bypass the internal queue and be delivered to the watch callback immediately, and arrive at the next event poll.
Note: the callback is called for events posted by the user through SDL_PushEvent(), but not for disabled events, nor for events by a filter callback set with SDL_SetEventFilter(), nor for events posted by the user through SDL_PeepEvents().
\param filter an SDL_EventFilter function to call when an event happens. \param userdata a pointer that is passed to filter. \returns true on success or false on failure; call SDL_GetError() for more information.
\threadsafety It is safe to call this function from any thread.
\since This function is available since SDL 3.2.0.
\sa SDL_RemoveEventWatch \sa SDL_SetEventFilter