Event Example

This sample code shows an example of:

• filtering window close events
• handling mouse events
• polling keyboard state
• detecting iconification

#include <stdio.h>
#include <stdlib.h>

#include "SDL.h"

/* This function may run in a separate event thread */
int FilterEvents(const SDL_Event *event) {
	static int boycott = 1;

	/* This quit event signals the closing of the window */
	if ( (event->type == SDL_QUIT) && boycott ) {
		printf("Quit event filtered out -- try again.\n");
		boycott = 0;
		return(0);
	}
	if ( event->type == SDL_MOUSEMOTION ) {
		printf("Mouse moved to (%d,%d)\n",
					event->motion.x, event->motion.y);
		return(0);	/* Drop it, we've handled it */
	}
	return(1);
}

int main(int argc, char *argv[])
{
	SDL_Event event;

	/* Initialize the SDL library (starts the event loop) */
	if ( SDL_Init(SDL_INIT_VIDEO) < 0 ) {
		fprintf(stderr,
			"Couldn't initialize SDL: %s\n", SDL_GetError());
		exit(1);
	}

	/* Clean up on exit, exit on window close and interrupt */
	atexit(SDL_Quit);

	/* Ignore key events */
	SDL_EventState(SDL_KEYDOWN, SDL_IGNORE);
	SDL_EventState(SDL_KEYUP, SDL_IGNORE);

	/* Filter quit and mouse motion events */
	SDL_SetEventFilter(FilterEvents);

	/* The mouse isn't much use unless we have a display for reference */
	if ( SDL_SetVideoMode(640, 480, 8, 0) == NULL ) {
		fprintf(stderr, "Couldn't set 640x480x8 video mode: %s\n",
							SDL_GetError());
		exit(1);
	}

	/* Loop waiting for ESC+Mouse_Button */
	while ( SDL_WaitEvent(&event) >= 0 ) {
		switch (event.type) {
			case SDL_ACTIVEEVENT: {
				if ( event.active.state & SDL_APPACTIVE ) {
					if ( event.active.gain ) {
						printf("App activated\n");
					} else {
						printf("App iconified\n");
					}
				}
			}
			break;
					
			case SDL_MOUSEBUTTONDOWN: {
				Uint8 *keys;

				keys = SDL_GetKeyState(NULL);
				if ( keys[SDLK_ESCAPE] == SDL_PRESSED ) {
					printf("Bye bye...\n");
					exit(0);
				}
				printf("Mouse button pressed\n");
			}
			break;

			case SDL_QUIT: {
				printf("Quit requested, quitting.\n");
				exit(0);
			}
			break;
		}
	}
	/* This should never happen */
	printf("SDL_WaitEvent error: %s\n", SDL_GetError());
	exit(1);
}