Here’s a piece of code to help changing the main display with Quartz Display Services for a 2 displays configuration

#include <ApplicationServices/ApplicationServices.h>

#define MAX_DISPLAYS 32

int main (int argc, const char ** argv) {

CGDirectDisplayID activeDisplays[MAX_DISPLAYS]; CGDisplayErr err; CGDisplayCount displayCount; CGDisplayConfigRef config;

err = CGGetActiveDisplayList(MAX_DISPLAYS, activeDisplays, &displayCount); if ( err != kCGErrorSuccess ) { printf(“Cannot get displays (%d)\n”, err); exit(1); }

CGBeginDisplayConfiguration(&config); CGConfigureDisplayOrigin(config,activeDisplays[1], 0, 0); //Set the second display as the new main display by positionning at 0,0 CGConfigureDisplayOrigin(config,activeDisplays[0], CGDisplayPixelsWide(activeDisplays[1])+1, 0); //Arrangement of the old main display to the right of the new main display CGCompleteDisplayConfiguration(config,kCGConfigureForSession);

return 0; }