Core Graphics rendering from another thread

renderQueue.m

- (UIImage *)renderInImageOfSize:(CGSize)size;
{
    UIGraphicsBeginImageContextWithOptions(size, NO, 0);
	
    // do drawing here
	
    UIImage *result = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return result;
}

UIImageView *view; // assume we have this
NSOperationQueue *renderQueue; // assume we have this
CGSize size = view.bounds.size;
[renderQueue addOperationWithBlock:^(){
    UIImage *image = [renderer renderInImageOfSize:size];
	[[NSOperationQueue mainQueue] addOperationWithBlock:^(){
		view.image = image;
	}];
}];

Source http://www.objc.io/issue-3/moving-pixels-onto-the-screen.html