iOS 利用Context裁剪图片

UIGraphicsBeginImageContext(newSize);

[image drawInRect:CGRectMake(0,0,newSize.width,newSize.width)];

UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

UIGraphicsBeginImageContext(image.size);
CGContextRef context = UIGraphicsGetCurrentContext();

CGRect rect = CGRectMake(0, 0, image.size.width, image.size.height);
CGContextAddEllipseInRect(context, rect);
CGContextClip(context); //进行剪切，所有context绘制只保留能够被当前path进行fill的区域
[image drawInRect:rect]; //绘制原图

UIImage *newimg = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();