A user-defined event type (event.user.*)
Defined in SDL_events.h
typedef struct SDL_UserEvent
{/**< SDL_USEREVENT through SDL_LASTEVENT-1 */
Uint32 type; /**< In milliseconds, populated using SDL_GetTicks() */
Uint32 timestamp; /**< The associated window if any */
Uint32 windowID; /**< User defined event code */
Sint32 code; void *data1; /**< User defined data pointer */
void *data2; /**< User defined data pointer */
} SDL_UserEvent;