普通版本完成的锯齿很严重 但是Ios系统中仅CGContextClearRect 并不存在cyclo等方法。 网上查了一些资料。 发现还是利用到了CG 中的Mask来实现
效果图：
  

这种效果可以自定义画笔的粗细等相关设置，不会像普通模式中出现比较严重的锯齿。

具体分析如下：
     1.获取需要隐藏View的layer的CGImageRef用于后面配合掩码
     2.开辟符合1的CGImageRef的CFMutableDataRef空间 给下面的掩码BitmapContext使用
     3.通过CFMutableDataRef获得CGDataProviderRef （maskCreate用到）
     3.BitmapContextCreate
     4.BitmapContext填充黑色 并且设置画笔相关(白色，宽度，线帽(cap))
     5.CGImageMaskCreate 将CGDataProviderRef  传入 则得到CGImageRef指向的是刚才创建BitmapContext。改变BitmapContext 则此CGImageRef内容也会改变
     6.CGImageCreateWithMask - 通过Mask的CGImageRef创建CGImageRef 此CGImageRef随 Maskde CGImageRef变化（所以 BitmapContext改变 Mask改变 mask掩码后的CGImageRef改变）
     7.释放

     8.手指触摸时，根据上一个CGPoint 和此次的CGPoint 给bitmapContext新增path 并且绘制。然后调用【self setNeedsDisplay】，在重绘中(-drawRect) 重新获取通过mask后的CGImageRef 获取最新的UIImage
     9.将最新的UIImage drawRect到界面


代码：
//
//  PLLScrathView.h
//  PLLScratchViewDemo
//
//  Created by liu poolo on 14-7-31.
//  Copyright (c) 2014年 liu poolo. All rights reserved.
//

#import <UIKit/UIKit.h>
#import <QuartzCore/QuartzCore.h>

@interface PLLScratchView : UIView
@property (nonatomic,assign) float sizeBrush;
-(void)setHideView:(UIView*) hideView;
@end

//
//  PLLScrathView.m
//  PLLScratchViewDemo
//
//  Created by liu poolo on 14-7-31.
//  Copyright (c) 2014年 liu poolo. All rights reserved.
//

#import "PLLScratchView.h"
@interface PLLScratchView(){
    CGContextRef _contextMask;//maskContext 用户touch 改变的context
    CGImageRef _scratchCGImg;//CGimageRef 封装_contextMask 图片信息 _contextMask改变 跟着改变 直到 调用生成UIImage
    CGPoint currPonit;
    CGPoint prePoint;
}
@end

@implementation PLLScratchView
@synthesize sizeBrush;
- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        [self setOpaque:NO];
        //设置透明 如果不透明就没法看到下一层了
        self.sizeBrush=10.0f;
    }
    return self;
}

- (void)drawRect:(CGRect)rect
{
    [super drawRect:rect];
    UIImage* imageToDraw=[UIImage imageWithCGImage:_scratchCGImg];
    [imageToDraw drawInRect:self.frame];
}
//setSizeBrush before setHideView
-(void)setHideView:(UIView*) hideView{
    CGColorSpaceRef colorSpace=CGColorSpaceCreateDeviceGray();
    CGFloat scale = [UIScreen mainScreen].scale;
   
    //获得当前传入View的CGImage
    UIGraphicsBeginImageContextWithOptions(hideView.bounds.size, NO, 0);
    hideView.layer.contentsScale=scale;
    [hideView.layer renderInContext:UIGraphicsGetCurrentContext()];
    CGImageRef hideCGImg=UIGraphicsGetImageFromCurrentImageContext().CGImage;
    UIGraphicsEndImageContext();
   
    //绘制Bitmap掩码
    size_t width=CGImageGetWidth(hideCGImg);
    size_t height=CGImageGetHeight(hideCGImg);
   
    CFMutableDataRef pixels;
    pixels=CFDataCreateMutable(NULL, width*height);
    //创建一个可变的dataRef 用于bitmap存储记录
    _contextMask = CGBitmapContextCreate(CFDataGetMutableBytePtr(pixels), width, height , 8, width, colorSpace, kCGImageAlphaNone);
   
    //数据提供者
    CGDataProviderRef dataProvider=CGDataProviderCreateWithCFData(pixels);
   
    //填充黑色背景 mask中黑色范围为显示内容 白色为不显示
    CGContextSetFillColorWithColor(_contextMask, [UIColor blackColor].CGColor);
    CGContextFillRect(_contextMask, self.frame);
   
    CGContextSetStrokeColorWithColor(_contextMask, [UIColor whiteColor].CGColor);
    CGContextSetLineWidth(_contextMask, self.sizeBrush);
    CGContextSetLineCap(_contextMask, kCGLineCapRound);
   
    CGImageRef mask=CGImageMaskCreate(width, height, 8, 8, width, dataProvider, nil, NO);
    _scratchCGImg=CGImageCreateWithMask(hideCGImg, mask);

    CGImageRelease(mask);
    CGColorSpaceRelease(colorSpace);
   
}

-(void)scratchViewFrom:(CGPoint)startPoint toEnd:(CGPoint)endPoint{
    float scale=[UIScreen mainScreen].scale;
    //CG的Y与UI的是反的 UI的y0在左上角 CG在左下
    CGContextMoveToPoint(_contextMask, startPoint.x*scale, (self.frame.size.height-startPoint.y)*scale);
    CGContextAddLineToPoint(_contextMask, endPoint.x*scale,(self.frame.size.height-endPoint.y)*scale);
    CGContextStrokePath(_contextMask);
    [self setNeedsDisplay];
}

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
    [super touchesBegan:touches withEvent:event];
}


-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{
    [super touchesMoved:touches withEvent:event];
    UITouch *touch=[touches anyObject];
    currPonit=[touch locationInView:self];
    prePoint=[touch previousLocationInView:self];
    [self scratchViewFrom:prePoint toEnd:currPonit];
}

-(void)toucheseEnd:(NSSet *)touches withEvent:(UIEvent *)event{
    [super touchesEnded:touches withEvent:event];
    UITouch *touch=[touches anyObject];
    currPonit=[touch locationInView:self];
    prePoint=[touch previousLocationInView:self];
    [self scratchViewFrom:prePoint toEnd:currPonit];
}


-(void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event{
    [super touchesCancelled:touches withEvent:event];
}


@end

[ios]ios-Demo4脱衣服/刮奖app-专业