SDL Guide 中文译版(四)[2]

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); }

打开音频设备

    sdl_audiospec wanted;
    extern void fill_audio(void *udata, uint8 *stream, int len);

    /* set the audio format */
    wanted.freq = 22050;
    wanted.format = audio_s16;
    wanted.channels = 2;    /* 1 = mono, 2 = stereo */
    wanted.samples = 1024;  /* good low-latency value for callback */
    wanted.callback = fill_audio;
    wanted.userdata = null;

    /* open the audio device, forcing the desired format */
    if ( sdl_openaudio(&wanted, null) < 0 ) {
        fprintf(stderr, "couldn't open audio: %s\n", sdl_geterror());
        return(-1);
    }
    return(0);

播放音频

    static uint8 *audio_chunk;
    static uint32 audio_len;
    static uint8 *audio_pos;

    /* the audio function callback takes the following parameters:
       stream:  a pointer to the audio buffer to be filled
       len:     the length (in bytes) of the audio buffer
    */
    void fill_audio(void *udata, uint8 *stream, int len)
    {
        /* only play if we have data left */
        if ( audio_len == 0 )
            return;

        /* mix as much data as possible */
        len = ( len > audio_len ? audio_len : len );
        sdl_mixaudio(stream, audio_pos, len, sdl_mix_maxvolume)
        audio_pos += len;
        audio_len -= len;
    }

    /* load the audio data ... */

    ;;;;;

    audio_pos = audio_chunk;

    /* let the callback function play the audio chunk */
    sdl_pauseaudio(0);

    /* do some processing */

    ;;;;;

    /* wait for sound to complete */
    while ( audio_len > 0 ) {
        sdl_delay(100);         /* sleep 1/10 second */
    }
    sdl_closeaudio();

列出所有cdrom

    #include "sdl.h"

    /* initialize sdl first */
    if ( sdl_init(sdl_init_cdrom) < 0 ) {
        fprintf(stderr, "couldn't initialize sdl: %s\n",sdl_geterror());
        exit(1);
    }
    atexit(sdl_quit);

    /* find out how many cd-rom drives are connected to the system */
    printf("drives available: %d\n", sdl_cdnumdrives());
    for ( i=0; i<sdl_cdnumdrives(); ++i ) {
        printf("drive %d:  \"%s\"\n", i, sdl_cdname(i));
    }

打开缺省cdrom驱动器

    sdl_cd *cdrom;
    cdstatus status;
    char *status_str;

    cdrom = sdl_cdopen(0);
    if ( cdrom == null ) {
        fprintf(stderr, "couldn't open default cd-rom drive: %s\n",
                        sdl_geterror());
        exit(2);
    }

    status = sdl_cdstatus(cdrom);
    switch (status) {
        case cd_trayempty:
            status_str = "tray empty";
            break;
        case cd_stopped:
            status_str = "stopped";
            break;
        case cd_playing:
            status_str = "playing";
            break;
        case cd_paused:
            status_str = "paused";
            break;
        case cd_error:
            status_str = "error state";
            break;
    }
    printf("drive status: %s\n", status_str);
    if ( status >= cd_playing ) {
        int m, s, f;
        frames_to_msf(cdrom->cur_frame, &m, &s, &f);
        printf("currently playing track %d, %d:%2.2d\n",
        cdrom->track[cdrom->cur_track].id, m, s);
    }

列出cd上所有音轨

    sdl_cd *cdrom;          /* assuming this has already been set.. */
    int i;
    int m, s, f;

    sdl_cdstatus(cdrom);
    printf("drive tracks: %d\n", cdrom->numtracks);
    for ( i=0; i<cdrom->numtracks; ++i ) {
        frames_to_msf(cdrom->track[i].length, &m, &s, &f);
        if ( f > 0 )
            ++s;
        printf("\ttrack (index %d) %d: %d:%2.2d\n", i,
        cdrom->track[i].id, m, s);
    }

播放cd

    sdl_cd *cdrom;          /* assuming this has already been set.. */

    // play entire cd:
    if ( cd_indrive(sdl_cdstatus(cdrom)) )
        sdl_cdplaytracks(cdrom, 0, 0, 0, 0);

        // play last track:
        if ( cd_indrive(sdl_cdstatus(cdrom)) ) {
            sdl_cdplaytracks(cdrom, cdrom->numtracks-1, 0, 0, 0);
        }

        // play first and second track and 10 seconds of third track:
        if ( cd_indrive(sdl_cdstatus(cdrom)) )
            sdl_cdplaytracks(cdrom, 0, 0, 2, 10);

基于时间的游戏主循环

#define tick_interval    30

uint32 timeleft(void)
{
    static uint32 next_time = 0;
    uint32 now;

    now = sdl_getticks();
    if ( next_time <= now ) {
        next_time = now+tick_interval;
        return(0);
    }
    return(next_time-now);
}


/* main game loop

    while ( game_running ) {
        updategamestate();