/*

cc -g  -o modewhacker -framework CoreGraphics modewhacker.c

*/

#include <ApplicationServices/ApplicationServices.h>

#include <stdlib.h>

#include <unistd.h>

static int numberForKey( CFDictionaryRef desc, CFStringRef key )

{

    CFNumberRef value;

    int num = 0;

    if ( (value = CFDictionaryGetValue(desc, key)) == NULL )

        return 0;

    CFNumberGetValue(value, kCFNumberIntType, &num);

    return num;

}

static void printDesc( CFDictionaryRef desc )

{

    char * msg;

    if ( CFDictionaryGetValue(desc, kCGDisplayModeUsableForDesktopGUI) == kCFBooleanTrue )

        msg = "Supports Aqua GUI";

    else

        msg = "Not for Aqua GUI";

    printf( "\t%d x %d,\t%d BPP,\t%d Hz\t(%s)\n",

            numberForKey(desc, kCGDisplayWidth),

            numberForKey(desc, kCGDisplayHeight),

            numberForKey(desc, kCGDisplayBitsPerPixel),

            numberForKey(desc, kCGDisplayRefreshRate),

            msg );

}

struct myMode

{

    size_t width;

    size_t height;

    size_t bitsPerPixel;

};

const struct myMode myModeList[] =

{

    { 640, 480, 8 },        /* 640 x 480,  8 bits per pixel */

    { 832, 624, 16 },       /* 832 x 624, 16 bits per pixel */

    { 1120, 832, 32 },      /* 1120 x 832, 32 bits per pixel */

};

static void modewhacker( CGDirectDisplayID dspy )

{

    int i;

    CFDictionaryRef mode;

    CFDictionaryRef originalMode;

    boolean_t exactMatch;

    CGDisplayErr err;

    originalMode = CGDisplayCurrentMode( dspy );

    if ( originalMode == NULL )

    {

        printf( "Display is invalid\n" );

        return;

    }

    for ( i = 0; i < (sizeof myModeList / sizeof myModeList[0]); ++i )

    {

        printf( "Display 0x%x: Looking for %ld x %ld, %ld Bits Per Pixel\n",

                (unsigned int)dspy,

                myModeList[i].width,

                myModeList[i].height,

                myModeList[i].bitsPerPixel );

        mode = CGDisplayBestModeForParameters(dspy,

                                              myModeList[i].bitsPerPixel,

                                              myModeList[i].width,

                                              myModeList[i].height,

                                              &exactMatch);

        if ( exactMatch )

            printf( "Found an exact match, switching modes:\n" );

        else

            printf( "Found a mode, switching modes:\n" );

        printDesc( mode );

        sleep( 1 ); // Short pause, then switch

        err = CGDisplaySwitchToMode(dspy, mode);

        if ( err != CGDisplayNoErr )

        {

            printf( "Oops!  Mode switch failed?!?? (%d)\n", err );

            break;

        }

        printf( "Pausing for 5 seconds...\n" );

        sleep( 5 );

    }

    err = CGDisplaySwitchToMode(dspy, originalMode);

    if ( err != CGDisplayNoErr )

        printf( "Oops!  Mode restore failed?!?? (%d)\n", err );

}

/*

 * Arbitrary value.  For purposes of this example I don't expect

 * more than this many on a typical desktop system...

 */

#define kMaxDisplays    16

int

main(int argc, const char *argv[])

{

    CGDirectDisplayID display[kMaxDisplays];

    CGDisplayCount numDisplays;

    CGDisplayCount i;

    CGDisplayErr err;

    err = CGGetActiveDisplayList(kMaxDisplays,

                                 display,

                                 &numDisplays);

    if ( err != CGDisplayNoErr )

    {

        printf("Cannot get displays (%d)\n", err);

        exit( 1 );

    }

    printf( "%d displays found\n", (int)numDisplays );

    for ( i = 0; i < numDisplays; ++i )

    {

        modewhacker(display[i]);

    }

    exit(0);

}