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;  

    }