效果图:

代码部分:

#import "ViewController.h"@interface ViewController ()@property (nonatomic, strong) CALayer *imageLayer;@property (nonatomic, strong) CALayer *maskViewLayer;@property (nonatomic, strong) UIImage *contentImage;@property (nonatomic, strong) UIImage *maskViewContentImage;@end@implementation ViewController- (void)viewDidLoad {    [super viewDidLoad];        self.view.backgroundColor = [UIColor blackColor];        self.contentImage = [UIImage imageNamed:@"原始图片"];    self.maskViewContentImage = [UIImage imageNamed:@"maskLayerContents"];        self.imageLayer = [CALayer layer];    self.imageLayer.frame = CGRectMake(0, 0, 200, 200);    self.imageLayer.contents = (id)self.contentImage.CGImage;        self.maskViewLayer = [CALayer layer];    self.maskViewLayer.frame = CGRectMake(-200, -200, 200, 200);    self.maskViewLayer.contents = (id)self.maskViewContentImage.CGImage;        // self.imageLayer的局部区域的显示与否可以通过mask的alpha通道来决定    self.imageLayer.mask = self.maskViewLayer;        [self.view.layer addSublayer:self.imageLayer];    }- (void)touchesBegan:(NSSet
     
       *)touches withEvent:(UIEvent *)event{    self.maskViewLayer.frame = self.imageLayer.bounds;}
     

github: