What problem does this solve or what need does it fill?

increasing iOS and macOS game performance whilst saving battery live is a hard task but can be done quite easily, since macOS and iOS usually fix application framerate (with the exclusion to scrollviews or when programmatically demmanded). Currently a basic bevy app uses ~100% cpu on mac, which is a shame because it can be lower

What solution would you like?

Since application framerate is capped, using CADisplayLink on iOS and CVDisplayLink on macOS will give you a non-blocking 60 tick per second callback

What alternative(s) have you considered?

There's no other way on macOS , because the most common run loop [NSApp getevent.....] is really slow and CoreVideo bypasses all of the objc event system

Additional context

As someone who has implemented both CADisplayLink and CVDisplayLink once in the past. I can assure you it saves alot on cpu usage going from ~>100% to <20% which in turn saves on a lot of battery life. Also because apple ctr-alt-deleted there good old CoreVideo documention here’s a quick overview in obj-c (even though corevideo is mostly a c-api):

//create a display link
CVDisplayLinkRef displayLink;
CGDirectDisplayID   displayID = CGMainDisplayID();
CVReturn  error = kCVReturnSuccess;
error = CVDisplayLinkCreateWithCGDisplay(displayID, &displayLink);
if (error){
      NSLog(@"error:%d", error);
      displayLink = NULL;
}
//link callback
CVDisplayLinkSetOutputCallback(displayLink, renderCallback, (__bridge void *)self);
//start
CVDisplayLinkStart(displayLink);

//callback
CVReturn renderCallback(CVDisplayLinkRef displayLink, 
                               const CVTimeStamp *inNow, 
                               const CVTimeStamp *inOutputTime, 
                               CVOptionFlags flagsIn, 
                               CVOptionFlags *flagsOut, 
                               void *displayLinkContext){
    @autoreleasepool {
        update();
        //get access to the main thread when drawing to screen (this method is also blocking but way less demanding than the NSApp runloop)
        dispatch_sync(dispatch_get_main_queue(), ^{ 
            [gview setNeedsDisplay:YES];
        });
    }
    return 0;
}