iOS怎样画出图片的一部分

(UIImage )croppedImage:(UIImage )image

{

if (image)

{

float min = MIN(image.size.width,image.size.height);

CGRect rectMAX = CGRectMake(0, 0, min, min/2);

CGImageRef subImageRef = CGImageCreateWithImageInRect(image.CGImage, rectMAX);

UIGraphicsBeginImageContext(rectMAX.size);

CGContextRef context = UIGraphicsGetCurrentContext();

CGContextDrawImage(context, CGRectMake(0, 0, min, min), subImageRef);

UIImage *viewImage = [UIImage imageWithCGImage:subImageRef];

UIGraphicsEndImageContext();

CGImageRelease(subImageRef);

return viewImage;

}

return nil;

}