iOS如何截屏或view生成image之后支持背景透明

- (UIImage *)makeImageWithView:(UIView *)orgView withSize:(CGSize)size

{

    CGFloat scale = [UIScreen mainScreen].scale;

    UIGraphicsBeginImageContextWithOptions(orgView.bounds.size, NO, scale);

    CGContextRef context = UIGraphicsGetCurrentContext();

    CGContextSaveGState(context);

    [orgView.layer renderInContext:context];

    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    //把像素rect 转化为点rect（如无转化则按原图像素取部分图片）

    CGFloat x= orgView.frame.origin.x*scale,y=orgView.frame.origin.y*scale,w=orgView.frame.size.width*scale,h=orgView.frame.size.height*scale;

    CGRect dianRect = CGRectMake(x, y, w, h);

    //截取部分图片并生成新图片

    CGImageRef sourceImageRef = [image CGImage];

    CGImageRef newImageRef = CGImageCreateWithImageInRect(sourceImageRef, dianRect);

    UIImage *newImage = [UIImage imageWithCGImage:newImageRef scale:scale orientation:UIImageOrientationUp];

    return newImage;

}