CALayer mask Layer animating - uikit

Question

I want to mask CALayer with another layer whose frame I want to keep changing in every draw call thereby animating. Is it possible to do change the frame of mask layer in every draw call rather than making a new mask layer?

Answer 1

Try the following code. This code will run on Cocoa App for macOS. Kindly change the classes accordingly if you are going for Cocoa Touch for iOS. I hope this works for you.
// ViewController.h
import
#interface ViewController : NSViewController{
CALayer * maskLayer;
CALayer * Layer;
}
// ViewController.m
#implementation ViewController
-(void)viewDidLoad{
[super viewDidLoad];
maskLayer = [CALayer layer];
Layer = [CALayer layer];
Layer.backgroundColor = [[NSColor blueColor] CGColor];
Layer.frame = CGRectMake(20, 20, 720, 900);
Layer.contents = [NSImage imageNamed:#"bg1"];
maskLayer.frame = CGRectMake(20, 20, 720, 900);
maskLayer.opacity = 0.5;
[maskLayer mask];
maskLayer.contents = [NSImage imageNamed:#"bg"];
[self.view.layer addSublayer:Layer];
[self.view.layer addSublayer:maskLayer];
[self maskLayerAnimation];
}
-(void)maskLayerAnimation{
[CATransaction begin];
CABasicAnimation* fadeAnim = [CABasicAnimation animationWithKeyPath:#"opacity"];
fadeAnim.fromValue = [NSNumber numberWithFloat:1.0];
fadeAnim.toValue = [NSNumber numberWithFloat:0.0];
fadeAnim.duration = 5.0;
[CATransaction setCompletionBlock:^{
NSLog(#"animation completed");
maskLayer.frame = CGRectMake(20, 20, 720, 700);
maskLayer.contents = [NSImage imageNamed:#"bg2"];
}];;
[maskLayer addAnimation:fadeAnim forKey:#"opacity"];
[CATransaction commit];
}