以下为大家提供一种绘制不规则图形的方法，实现原理利用图像的遮盖。
//// 这种是路径遮盖法
+ (UIImage*)maskImage:(UIImage*)originImage toPath:(UIBezierPath*)path
{
UIGraphicsBeginImageContextWithOptions(originImage.size, NO, 0);
[path addClip];
[originImage drawAtPoint:CGPointZero];
UIImage* img = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return img;
}
////为图像创建透明区域
+ (CGImageRef)CopyImageAndAddAlphaChannel:(CGImageRef)sourceImage
{
CGImageRef retVal = NULL;
size_t width = CGImageGetWidth(sourceImage);
size_t height = CGImageGetHeight(sourceImage);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef offscreenContext = CGBitmapContextCreate(NULL, width, height,
8, 0, colorSpace,
kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Little);
if (offscreenContext != NULL)
{
CGContextDrawImage(offscreenContext, CGRectMake(0, 0, width, height), sourceImage);
retVal = CGBitmapContextCreateImage(offscreenContext);
CGContextRelease(offscreenContext);
}
CGColorSpaceRelease(colorSpace);
return retVal;
}
/////利用图像遮盖
+ (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, true);
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 = [ImageUtil 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;
}