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生成一个不规则图形的方式，比如下面的效果： 需要将文字部分用多边形圈起来。这里做了一个多边形的图，然后填充为黑色，设置了alpha透明度，就产生了这样的效果。 代码如下：
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- (void)loadView { [[UIApplication sharedApplication] setStatusBarHidden:YES withAnimation: UIStatusBarAnimationSlide]; UIImage *image=[UIImage imageNamed:@"1.jpg"];? UIImageView *backView=[[UIImageView alloc] initWithFrame:[[UIScreen mainScreen] applicationFrame]]; backView.image=image; backView.alpha=0.6;? CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); CGContextRef context = CGBitmapContextCreate(nil,768,1024,8,0, colorSpace,kCGImageAlphaPremultipliedLast); CFRelease(colorSpace);? UIImageView *contentView = [[UIImageView alloc] initWithFrame:[[UIScreen mainScreen] applicationFrame]]; CGColorRef fillColor = [[UIColor blackColor] CGColor]; CGContextSetFillColor(context, CGColorGetComponents(fillColor)); CGContextBeginPath(context); CGContextMoveToPoint(context, 160.0f, 230.0f); CGContextAddLineToPoint(context, 600.0f, 230.0f); CGContextAddLineToPoint(context, 600.0f, 100.0f); CGContextAddLineToPoint(context, 370.0f, 50.0f); CGContextAddLineToPoint(context, 200.0f, 100.0f); CGContextClosePath(context); CGContextFillPath(context);? contentView.image=[[UIImage alloc] initWithCGImage:CGBitmapContextCreateImage(context)]; contentView.alpha=0.3; CGContextRelease(context);? self.view=[[UIView alloc] initWithFrame:[[UIScreen mainScreen] applicationFrame]]; [self.view addSubview:backView]; [self.view addSubview:contentView];?? [backView release]; [contentView release]; [image release];}