How does on-screen color inversion work in OS X?

Question

This is what OS X\'s built in color inversion feature can turn your screen into:

Answer 1

The way OS X itself does it is through a set of undocumented CoreGraphics API calls. I don't think they're declared in any official header file, but you can always just declare the prototypes yourself.

// clang -g -O2 -std=c11 -Wall -framework ApplicationServices

#include 
#include 

CG_EXTERN bool CGDisplayUsesInvertedPolarity(void);
CG_EXTERN void CGDisplaySetInvertedPolarity(bool invertedPolarity);

int
main(int argc, char** argv)
{
    bool isInverted = CGDisplayUsesInvertedPolarity();
    printf("isInverted = %d\n", isInverted);

    sleep(2);
    CGDisplaySetInvertedPolarity(!isInverted);
    printf("Polarity is now: %d\n", CGDisplayUsesInvertedPolarity());

    sleep(2);
    CGDisplaySetInvertedPolarity(isInverted);
    printf("Polarity is now: %d\n", CGDisplayUsesInvertedPolarity());

    return 0;
}

There are similar API calls for other accessibility features, such as grayscale:

CG_EXTERN bool CGDisplayUsesForceToGray(void);
CG_EXTERN void CGDisplayForceToGray(bool forceToGray);