Capture screen with CGDisplayStream

Question

I'm trying to implement a feature in my app that will record the screen. I have bits of code that I have found in some sample code and a WWDC 2012 video.

So far I have this.

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {

    // Get a list of displays.  Copied from working apple source code.
    [self getDisplayList];

    DisplayRegistrationCallBackSuccessful = NO;

    // Register the event for modifying displays.
    CGError err =  CGDisplayRegisterReconfigurationCallback(DisplayRegisterReconfigurationCallback, NULL);
    if (err == kCGErrorSuccess) {
        DisplayRegistrationCallBackSuccessful = YES;
    }

    // Insert code here to initialize your application

    const void *keys[1] = { kCGDisplayStreamSourceRect };
    const void *values[1] = { CGRectCreateDictionaryRepresentation(CGRectMake(0, 0, 100, 100)) };
    CFDictionaryRef properties = CFDictionaryCreate(NULL, keys, values, 1, NULL, NULL);

    stream = CGDisplayStreamCreate(displays[0], 100, 100, '420f', properties,
                                                  ^(CGDisplayStreamFrameStatus status, uint64_t displayTime, IOSurfaceRef frameSurface, CGDisplayStreamUpdateRef updateRef) {
                                                      NSLog(@"Next Frame"); // This line is never called.
                                                  });

    runLoop = CGDisplayStreamGetRunLoopSource(stream);

    CGError err = CGDisplayStreamStart(stream); 
    if (err == CGDisplayNoErr) {
        NSLog(@"Works");
    } else {
        NSLog(@"Error: %d", err);
    }
}

The problem I am encountering is that the callback block for the DisplayStream is not being called. I am not getting any errors or warnings. Is there something I'm missing or that I've done wrong?

Answer 1

I solved the problem by using CGDisplayStreamCreateWithDispatchQueue and passing dispatch_queue_create("queue for dispatch", NULL); as the queue.

Answer 2

For what it's worth, it looks like you're getting the runloop source, but then not adding it to the current run loop (CFRunLoopAddSource)