OSIT-AE-App-Native-Electron/scripts/display_control.m

/*
 * display_control.m
 * Native macOS CLI for programmatic display mirror/extend control.
 *
 * Derived from the OSIT MasterKey app (LegacyUtilities.m, Ian Kohl 2019).
 * Uses CoreGraphics APIs — no external dependencies (no displayplacer/Homebrew required).
 *
 * Build: run scripts/build-display-control.sh on a Mac (requires Xcode Command Line Tools)
 * Usage: display_control <mirror|extend|status>
 */

#import <Cocoa/Cocoa.h>
#include <Carbon/Carbon.h>

#define MAX_DISPLAYS 8

static int mirror_displays(void) {
    CGDirectDisplayID onlineDspys[MAX_DISPLAYS] = {0};
    CGDisplayCount numOnline = 0;

    CGGetOnlineDisplayList(MAX_DISPLAYS, onlineDspys, &numOnline);

    if (numOnline < 2) {
        fprintf(stderr, "No secondary display detected (%u online).\n", numOnline);
        return 1;
    }

    CGDirectDisplayID mainID = CGMainDisplayID();

    CGDisplayConfigRef config;
    CGError err = CGBeginDisplayConfiguration(&config);
    if (err != kCGErrorSuccess) {
        fprintf(stderr, "CGBeginDisplayConfiguration failed: %d\n", err);
        return 1;
    }

    BOOL any_configured = NO;
    for (CGDisplayCount i = 0; i < numOnline; i++) {
        if (onlineDspys[i] != mainID) {
            err = CGConfigureDisplayMirrorOfDisplay(config, onlineDspys[i], mainID);
            if (err != kCGErrorSuccess) {
                fprintf(stderr, "CGConfigureDisplayMirrorOfDisplay failed: %d\n", err);
                CGCancelDisplayConfiguration(config);
                return 1;
            }
            any_configured = YES;
        }
    }

    if (!any_configured) {
        CGCancelDisplayConfiguration(config);
        fprintf(stderr, "No secondary displays to mirror.\n");
        return 1;
    }

    err = CGCompleteDisplayConfiguration(config, kCGConfigurePermanently);
    if (err != kCGErrorSuccess) {
        fprintf(stderr, "CGCompleteDisplayConfiguration failed: %d\n", err);
        return 1;
    }

    printf("Mirrored %u display(s).\n", numOnline - 1);
    return 0;
}

static int extend_displays(void) {
    CGDirectDisplayID onlineDspys[MAX_DISPLAYS] = {0};
    CGDirectDisplayID activeDspys[MAX_DISPLAYS] = {0};
    CGDisplayCount numOnline = 0, numActive = 0;

    CGGetOnlineDisplayList(MAX_DISPLAYS, onlineDspys, &numOnline);
    CGGetActiveDisplayList(MAX_DISPLAYS, activeDspys, &numActive);

    if (numOnline < 2) {
        fprintf(stderr, "No secondary display detected (%u online).\n", numOnline);
        return 1;
    }

    if (numActive >= numOnline) {
        printf("Displays already extended.\n");
        return 0;
    }

    CGDirectDisplayID mainID = CGMainDisplayID();

    CGDisplayConfigRef config;
    CGError err = CGBeginDisplayConfiguration(&config);
    if (err != kCGErrorSuccess) {
        fprintf(stderr, "CGBeginDisplayConfiguration failed: %d\n", err);
        return 1;
    }

    for (CGDisplayCount i = 0; i < numOnline; i++) {
        if (onlineDspys[i] != mainID) {
            // kCGNullDirectDisplay as master = un-mirror (extend)
            err = CGConfigureDisplayMirrorOfDisplay(config, onlineDspys[i], kCGNullDirectDisplay);
            if (err != kCGErrorSuccess) {
                fprintf(stderr, "CGConfigureDisplayMirrorOfDisplay(null) failed: %d\n", err);
                CGCancelDisplayConfiguration(config);
                return 1;
            }
        }
    }

    err = CGCompleteDisplayConfiguration(config, kCGConfigurePermanently);
    if (err != kCGErrorSuccess) {
        fprintf(stderr, "CGCompleteDisplayConfiguration failed: %d\n", err);
        return 1;
    }

    printf("Displays extended.\n");
    return 0;
}

static void print_status(void) {
    CGDirectDisplayID onlineDspys[MAX_DISPLAYS] = {0};
    CGDirectDisplayID activeDspys[MAX_DISPLAYS] = {0};
    CGDisplayCount numOnline = 0, numActive = 0;

    CGGetOnlineDisplayList(MAX_DISPLAYS, onlineDspys, &numOnline);
    CGGetActiveDisplayList(MAX_DISPLAYS, activeDspys, &numActive);

    printf("online=%u active=%u %s\n",
           numOnline, numActive,
           (numOnline > 1 && numActive < numOnline) ? "mirrored" : "extended");
}

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        if (argc < 2) {
            fprintf(stderr, "Usage: display_control <mirror|extend|status>\n");
            return 1;
        }

        const char *cmd = argv[1];

        if (strcmp(cmd, "mirror") == 0) {
            return mirror_displays();
        } else if (strcmp(cmd, "extend") == 0) {
            return extend_displays();
        } else if (strcmp(cmd, "status") == 0) {
            print_status();
            return 0;
        } else {
            fprintf(stderr, "Unknown command: %s\nUsage: display_control <mirror|extend|status>\n", cmd);
            return 1;
        }
    }
}