Quartz 2D 裁剪

参考

使用Quartz 2D 可以对图片进行裁剪，简单的可以裁剪一个矩形，复杂的可以根据CGPath实现裁剪，也可以使用UIBezierPath进行裁剪，也可以使用一个UIImage做为mask进行裁剪。

对于如下图片，不使用裁剪时，显示全部内容

使用CGContextClipToRect裁剪矩形，

UIImage* imageSrc = [UIImage imageNamed:@"island.png"];
	CGColorSpaceRef colorRef = CGColorSpaceCreateDeviceRGB();
	CGContextRef contextRef = CGBitmapContextCreate(nil, imageSrc.size.width, imageSrc.size.height, 8, imageSrc.size.width*4, colorRef, kCGImageAlphaPremultipliedFirst);
	CGContextClipToRect(contextRef, CGRectMake(30, 100, 200, 200));
	CGContextDrawImage(contextRef, CGRectMake(0, 0, imageSrc.size.width, imageSrc.size.height), imageSrc.CGImage);
	CGImageRef imageRef = CGBitmapContextCreateImage(contextRef);
	UIImage* imageDst = [UIImage imageWithCGImage:imageRef scale:[UIScreen mainScreen].scale orientation:UIImageOrientationUp];
	CGContextRelease(contextRef);
	CGColorSpaceRelease(colorRef);
	return imageDst;

结果如下：

使用CGPath 设定一个区域，然后裁剪path，

UIImage* imageSrc = [UIImage imageNamed:@"island.png"];
	CGColorSpaceRef colorRef = CGColorSpaceCreateDeviceRGB();
	CGContextRef contextRef = CGBitmapContextCreate(nil, imageSrc.size.width, imageSrc.size.height, 8, imageSrc.size.width*4, colorRef, kCGImageAlphaPremultipliedFirst);
	//[path addCurveToPoint:CGPointMake(120, 80) controlPoint1:CGPointMake(<#CGFloat x#>, <#CGFloat y#>) controlPoint2:<#(CGPoint)#>]
	CGMutablePathRef mutPath = CGPathCreateMutable();
	CGPathMoveToPoint(mutPath, NULL, 30, 160);
	CGPathAddLineToPoint(mutPath, NULL, 120, 80);
	CGPathAddLineToPoint(mutPath, NULL, 210, 160);
	CGPathAddLineToPoint(mutPath, NULL, 120, 280);
	CGPathCloseSubpath(mutPath);
	CGContextAddPath(contextRef, mutPath);
	CGContextClip(contextRef);
	CGContextDrawImage(contextRef, CGRectMake(0, 0, imageSrc.size.width, imageSrc.size.height), imageSrc.CGImage);
	CGImageRef imageRef = CGBitmapContextCreateImage(contextRef);
	UIImage* imageDst = [UIImage imageWithCGImage:imageRef scale:[UIScreen mainScreen].scale orientation:UIImageOrientationUp];
	CGContextRelease(contextRef);
	CGColorSpaceRelease(colorRef);
	return imageDst;

结果如下：

使用UIBezierPath 创建一个裁剪区域，

	
UIImage* imageSrc = [UIImage imageNamed:@"island.png"];
	CGColorSpaceRef colorRef = CGColorSpaceCreateDeviceRGB();
	CGContextRef contextRef = CGBitmapContextCreate(nil, imageSrc.size.width, imageSrc.size.height, 8, imageSrc.size.width*4, colorRef, kCGImageAlphaPremultipliedFirst);
	UIBezierPath* path = [UIBezierPath bezierPath];
	[path moveToPoint:CGPointMake(30, 160)];
//	[path addCurveToPoint:CGPointMake(140, 80) controlPoint1:CGPointMake(60, 60) controlPoint2:CGPointMake(90, 60)];
//	[path addCurveToPoint:CGPointMake(210, 160) controlPoint1:CGPointMake(130, 90) controlPoint2:CGPointMake(160, 120)];
//	[path addCurveToPoint:CGPointMake(140, 280) controlPoint1:CGPointMake(180, 200) controlPoint2:CGPointMake(140, 160)];
	[path addQuadCurveToPoint:CGPointMake(140, 100) controlPoint:CGPointMake(80, 120)];
	[path addQuadCurveToPoint:CGPointMake(240, 180) controlPoint:CGPointMake(180, 100)];
	[path addQuadCurveToPoint:CGPointMake(140, 280) controlPoint:CGPointMake(210, 240)];
	[path addQuadCurveToPoint:CGPointMake(30, 160) controlPoint:CGPointMake(80, 260)];
	[path closePath];
	[path addClip];
	
	CGContextDrawImage(contextRef, CGRectMake(0, 0, imageSrc.size.width, imageSrc.size.height), imageSrc.CGImage);
	CGImageRef imageRef = CGBitmapContextCreateImage(contextRef);
	UIImage* imageDst = [UIImage imageWithCGImage:imageRef scale:[UIScreen mainScreen].scale orientation:UIImageOrientationUp];
	CGContextRelease(contextRef);
	CGColorSpaceRelease(colorRef);
	return imageDst;

结果如下：

使用UIImage做为mask进行裁剪

使用 void CGContextClipToMask(CGContextRef c, CGRect rect,  CGImageRef mask) 

第一个参数表示context 指针

第二个参数表示clip到context的区域，也是mask 图片映射到context的区域

第三个参数表示mask的图片，对于裁剪区域Rect中的点是否变化取决于mask图中的alpha值，若alpha为0，则对应clip rect中的点为透明，如果alpha为1，则对应clip Rect中的点无变化。

另外CGContextClipToMask执行了类似  CGContextDrawImage 到rect区域的操作，不需要另外调用CGContextDrawImage。

例子：

下图为具有mask图片，图片中只有alpha值对于mask是有用的。

- (UIImage*)imageWithColor:(UIColor*)color maskImage:(UIImage*)maskImage
{
	UIImage* image =  maskImage;
	CGColorSpaceRef colorRef = CGColorSpaceCreateDeviceRGB();
	CGContextRef contextRef = CGBitmapContextCreate(nil, image.size.width, image.size.height, 8, image.size.width*4, colorRef, kCGImageAlphaPremultipliedFirst);
	CGRect rect = CGRectMake(0, 0, image.size.width, image.size.height);
	CGContextClipToMask(contextRef, rect, image.CGImage);
	CGContextSetFillColorWithColor(contextRef, color.CGColor);
	CGContextFillRect(contextRef,rect);
	CGImageRef imageRef = CGBitmapContextCreateImage(contextRef);
	UIImage* imageDst = [UIImage imageWithCGImage:imageRef scale:[UIScreen mainScreen].scale orientation:UIImageOrientationUp];
	CGImageRelease(imageRef);
	CGContextRelease(contextRef);
	CGColorSpaceRelease(colorRef);
	return imageDst;
}

在DrawRect中使用上述方法后，

- (void)drawRect:(CGRect)rect
{
	UIImage* image1 = [UIImage imageNamed:@"cloud.png"];
	[[self imageWithColor:[UIColor redColor] maskImage:image1] drawAtPoint:CGPointMake(0, 0)];
	
}

显示如下

修改maskRect区域，并为查看方便显示蓝色背景，代码如下

- (UIImage*)imageWithColor:(UIColor*)color maskImage:(UIImage*)maskImage
{
	UIImage* image =  maskImage;
	CGColorSpaceRef colorRef = CGColorSpaceCreateDeviceRGB();
	CGContextRef contextRef = CGBitmapContextCreate(nil, image.size.width, image.size.height, 8, image.size.width*4, colorRef, kCGImageAlphaPremultipliedFirst);

	CGContextSetFillColorWithColor(contextRef, [UIColor blueColor].CGColor);
	CGRect rect = CGRectMake(0, 0, image.size.width, image.size.height);
	CGContextFillRect(contextRef,rect);
	CGRect maskRect = CGRectMake(60, 0, image.size.width, image.size.height);
	CGContextClipToMask(contextRef, maskRect, image.CGImage);
	CGContextSetFillColorWithColor(contextRef, color.CGColor);
	CGContextFillRect(contextRef,rect);
	CGImageRef imageRef = CGBitmapContextCreateImage(contextRef);
	UIImage* imageDst = [UIImage imageWithCGImage:imageRef scale:[UIScreen mainScreen].scale orientation:UIImageOrientationUp];
	CGImageRelease(imageRef);
	CGContextRelease(contextRef);
	CGColorSpaceRelease(colorRef);
	return imageDst;
}

向右偏移60像素，结果如下