学步园

首先你必须要准备一个原图，和一个准备作为遮罩的掩码图（mask），这里有两点要注意，如果希望通过CGImageCreateWithMask函数去创建一个处理过的不规则的图片的话，那么你需要有一张原图是带alpha通道的图片，和一个不带alpha通道的遮罩图。

如何判断是否有alpha通道其实很简单，你在mac里右键显示简介的时候，有显示该图片的信息，其中一行就是显示是否有alpha通道。

当然其实有方法可以通过代码给一个没有alpha通道的图片加上alpha通道，然后再处理显示，具体代码如下（附送一个通过path去clip图片的）

+(UIImage*)maskImage:(UIImage*)originImage toPath:(UIBezierPath*)path{
    UIGraphicsBeginImageContextWithOptions(originImage.size, NO, 0);
    [path addClip];
    [originImage drawAtPoint:CGPointZero];
    UIImage* img = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return img;    
}


+ (UIImage*)maskImage:(UIImage *)image withMask:(UIImage *)maskImage {
	CGImageRef maskRef = maskImage.CGImage;
	CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(maskRef),
                                        CGImageGetHeight(maskRef),
                                        CGImageGetBitsPerComponent(maskRef),
                                        CGImageGetBitsPerPixel(maskRef),
                                        CGImageGetBytesPerRow(maskRef),
                                        CGImageGetDataProvider(maskRef), NULL, false);
	
	CGImageRef sourceImage = [image CGImage];
	CGImageRef imageWithAlpha = sourceImage;
	//add alpha channel for images that don't have one (ie GIF, JPEG, etc...)
	//this however has a computational cost
	if (CGImageGetAlphaInfo(sourceImage) == kCGImageAlphaNone) { 
		imageWithAlpha = CopyImageAndAddAlphaChannel(sourceImage);
	}
	
	CGImageRef masked = CGImageCreateWithMask(imageWithAlpha, mask);
	CGImageRelease(mask);
	
	release imageWithAlpha if it was created by CopyImageAndAddAlphaChannel
	if (sourceImage != imageWithAlpha) {
		CGImageRelease(imageWithAlpha);
	}
	
	UIImage* retImage = [UIImage imageWithCGImage:masked];
	CGImageRelease(masked);
	
	return retImage;
}

下面的是resize图片的代码

// resize the original image and return a new UIImage object
+ (UIImage *) resizeImage:(UIImage *)image size:(CGSize)newSize {
    UIGraphicsBeginImageContext(newSize);
    [image drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}