iOS多张图片合成一张

用法很简单，如下

#pragma mark - 多张图片合成一张
+ (UIImage *)mergedImages:(NSArray *)imagesArray {

    CGFloat maxWidth    = 440;//考虑手机屏幕宽度
    CGFloat totalHeight = 0;
    //计算图片的高度
    for (UIImage *image in imagesArray) {
        totalHeight += image.size.height * maxWidth / image.size.width;
    }

    //绘图上下文
    UIGraphicsBeginImageContext(CGSizeMake(maxWidth, totalHeight));

    totalHeight = 0;
    for (UIImage *image in imagesArray) {

        CGFloat imageWidth  = maxWidth;
        CGFloat imageHeight = image.size.height * maxWidth / image.size.width;

        [image drawInRect:CGRectMake(0, totalHeight, imageWidth, imageHeight)];
        totalHeight += imageHeight;
    }     //生成图片
    UIImage *resultingImage = UIGraphicsGetImageFromCurrentImageContext();

    //释放上下文
    UIGraphicsEndImageContext();

    return resultingImage;
}