画正方形image

    /**
     *  剪切图片为正方形
     *
     *  @param image   原始图片比如size大小为(400x200)pixels
     *  @param newSize 正方形的size比如400pixels
     *
     *  @return 返回正方形图片(400x400)pixels
     */
    - (UIImage *)squareImageFromImage:(UIImage *)image scaledToSize:(CGFloat)newSize {
        CGAffineTransform scaleTransform;
        CGPoint origin;  

        if (image.size.width > image.size.height) {
            //image原始高度为200，缩放image的高度为400pixels，所以缩放比率为2
            CGFloat scaleRatio = newSize / image.size.height;
            scaleTransform = CGAffineTransformMakeScale(scaleRatio, scaleRatio);
            //设置绘制原始图片的画笔坐标为CGPoint(-100, 0)pixels
            origin = CGPointMake(-(image.size.width - image.size.height) / 2.0f, 0);
        } else {
            CGFloat scaleRatio = newSize / image.size.width;
            scaleTransform = CGAffineTransformMakeScale(scaleRatio, scaleRatio);  

            origin = CGPointMake(0, -(image.size.height - image.size.width) / 2.0f);
        }  

        CGSize size = CGSizeMake(newSize, newSize);
        //创建画板为(400x400)pixels
        if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)]) {
            UIGraphicsBeginImageContextWithOptions(size, YES, 0);
        } else {
            UIGraphicsBeginImageContext(size);
        }  

        CGContextRef context = UIGraphicsGetCurrentContext();
        //将image原始图片(400x200)pixels缩放为(800x400)pixels
        CGContextConcatCTM(context, scaleTransform);
        //origin也会从原始(-100, 0)缩放到(-200, 0)
        [image drawAtPoint:origin];  

        //获取缩放后剪切的image图片
        image = UIGraphicsGetImageFromCurrentImageContext();  

        UIGraphicsEndImageContext();  

        return image;
    }