iOS 图片擦除

图片擦除：
实际上是俩张图片彻底叠加，将第一张图片的进行透明清除，显露出下面的图片，其实现效果：
git

@interface DrawPictureClearVC ()
@property (weak, nonatomic) IBOutlet UIView *backView;
@property (weak, nonatomic) IBOutlet UIImageView *imageView;
@end

@implementation DrawPictureClearVC

- (void)viewDidLoad {
    [super viewDidLoad];
    self.title = @"draw ImageClear";


    //给view添加一个是手势
    UIPanGestureRecognizer *panGesture = [[UIPanGestureRecognizer alloc]init];

    [panGesture addTarget:self action:@selector(pan:)];
    [self.backView addGestureRecognizer:panGesture];

}

-(void)pan:(UIPanGestureRecognizer *)pan{

    //获取当前点
    CGPoint moveP = [pan locationInView:self.backView];

    //获取擦除的矩形范围
    CGFloat wh = 30;
    CGFloat x = moveP.x - wh *0.5;
    CGFloat y = moveP.y - wh *0.5;

    CGRect rect = CGRectMake(x, y, wh, wh);

    //建立位图上下文
    UIGraphicsBeginImageContextWithOptions(self.backView.bounds.size, NO, 0);

    //获取当前上下文
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    //把控件上的内容渲染到上下文
    [self.imageView.layer renderInContext:ctx];
    //擦除图片
    CGContextClearRect(ctx, rect);

    //获取图片
    self.imageView.image = UIGraphicsGetImageFromCurrentImageContext();
    //关闭上下文
    UIGraphicsEndImageContext();    
}
- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

最后，附上相关的demo,Git：(https://github.com/hejiasu/Drawing)github