两个UIImage 叠加

-(UIImage *)addImage:(UIImage *)image1 toImage:(UIImage *)image2
{
    UIGraphicsBeginImageContext(image2.size);
    //Draw image2
    [image2 drawInRect:CGRectMake(0, 0, image2.size.width, image2.size.height)];
    //Draw image1
    [image1 drawInRect:CGRectMake(20, 20, image1.size.width, image1.size.height)];
    UIImage *resultImage=UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return resultImage;
}