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# Event Examples

## Filtering and Handling Events

    #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);
    }

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