合成二張圖片

+ (UIImage*)mergeImage:(UIImage*)first withImage:(UIImage*)second
{
    // get size of the first image
    CGImageRef firstImageRef = first.CGImage;
    CGFloat firstWidth = CGImageGetWidth(firstImageRef);
    CGFloat firstHeight = CGImageGetHeight(firstImageRef);
   
    // get size of the second image
    CGImageRef secondImageRef = second.CGImage;
    CGFloat secondWidth = CGImageGetWidth(secondImageRef);
    CGFloat secondHeight = CGImageGetHeight(secondImageRef);
   
    // build merged size
    CGSize mergedSize = CGSizeMake(MAX(firstWidth, secondWidth), MAX(firstHeight, secondHeight));
   
    // capture image context ref
    UIGraphicsBeginImageContext(mergedSize);
   
    //Draw images onto the context
    [first drawInRect:CGRectMake(0, 0, firstWidth, firstHeight)];
    [second drawInRect:CGRectMake(0, 0, secondWidth, secondHeight)];
   
    // assign context to new UIImage
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
   
    // end context
    UIGraphicsEndImageContext();
   
    return newImage;
}