图片镜像水平翻转,垂直翻转以及顺时针,逆时针旋转

let image = board.image!

 //水平翻转
   let flipImageOrientation = (image.imageOrientation.rawValue + 4) % 8
   let flipImage = UIImage(CGImage: image.CGImage!, scale: image.scale, orientation: UIImageOrientation(rawValue: flipImageOrientation)!)
   board.image = flipImage

  /******* 另外一种水平镜像翻转的写法 ***********/    
        //Quartz重绘图片
        let rect =  CGRectMake(0, 0, image .size.width , image .size.height);//创建矩形框
        //根据size大小创建一个基于位图的图形上下文
        UIGraphicsBeginImageContext(rect.size)
//        UIGraphicsBeginImageContextWithOptions(rect.size, false, 2)
        let currentContext = UIGraphicsGetCurrentContext();//获取当前quartz 2d绘图环境
        CGContextClipToRect(currentContext, rect);//设置当前绘图环境到矩形框
        CGContextRotateCTM(currentContext, CGFloat(M_PI)); //旋转180度
        //平移， 这里是平移座标系，跟平移图形是一个道理
        CGContextTranslateCTM(currentContext, -rect.size.width, -rect.size.height);
        CGContextDrawImage(currentContext, rect, image .CGImage);//绘图

        //翻转图片
        let drawImage =  UIGraphicsGetImageFromCurrentImageContext();//获得图片 

  //垂直翻转
  var flipImageOrientation = (image.imageOrientation.rawValue + 4) % 8
   flipImageOrientation += flipImageOrientation%2==0 ? 1 : -1
   let flipImage =  UIImage(CGImage:image.CGImage!,scale:image.scale,orientation:UIImageOrientation(rawValue: flipImageOrientation)!)
    board.image = flipImage

    //顺时针旋转
up -> right -> down -> left -> up

    //逆时针旋转
up -> left -> down -> right -> up

这其中的规律能否不用switch 而用rawValue来表示,待明天来继续研究

- (IBAction)btnClicked:(id)sender {
    UIImage * image = _imageView.image;
    _imageView.image = nil;
    //逆时针
    UIImageOrientation orientation = image.imageOrientation;
    switch (orientation) {
        case UIImageOrientationUp:
            orientation = UIImageOrientationLeft;
            break;
        case UIImageOrientationLeft:
            orientation = UIImageOrientationDown;
            break;
        case UIImageOrientationDown:
            orientation = UIImageOrientationRight;
            break;
        case UIImageOrientationRight:
            orientation = UIImageOrientationUp;
            break;
        default:
            break;
    }


    _imageView.image = [self image:image rotation:orientation];
}

- (UIImage *)image:(UIImage *)image rotation:(UIImageOrientation)orientation
{
    long double rotate = 0.0;
    CGRect rect;
    float translateX = 0;
    float translateY = 0;
    float scaleX = 1.0;
    float scaleY = 1.0;

    switch (orientation) {
        case UIImageOrientationLeft:
            rotate = M_PI_2;
            rect = CGRectMake(0, 0, image.size.height, image.size.width);
            translateX = 0;
            translateY = -rect.size.width;
            scaleY = rect.size.width/rect.size.height;
            scaleX = rect.size.height/rect.size.width;
            break;
        case UIImageOrientationRight:
            rotate = 3 * M_PI_2;
            rect = CGRectMake(0, 0, image.size.height, image.size.width);
            translateX = -rect.size.height;
            translateY = 0;
            scaleY = rect.size.width/rect.size.height;
            scaleX = rect.size.height/rect.size.width;
            break;
        case UIImageOrientationDown:
            rotate = M_PI;
            rect = CGRectMake(0, 0, image.size.width, image.size.height);
            translateX = -rect.size.width;
            translateY = -rect.size.height;
            break;
        default:
            rotate = 0.0;
            rect = CGRectMake(0, 0, image.size.width, image.size.height);
            translateX = 0;
            translateY = 0;
            break;
    }

    UIGraphicsBeginImageContext(rect.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    //做CTM变换
    CGContextTranslateCTM(context, 0.0, rect.size.height);
    CGContextScaleCTM(context, 1.0, -1.0);
    CGContextRotateCTM(context, rotate);
    CGContextTranslateCTM(context, translateX, translateY);

    CGContextScaleCTM(context, scaleX, scaleY);
    //绘制图片
    CGContextDrawImage(context, CGRectMake(0, 0, rect.size.width, rect.size.height), image.CGImage);

    UIImage *newPic = UIGraphicsGetImageFromCurrentImageContext();

    return newPic;
}