沿任一轴翻转UIImage

问题描述

我试图创建一个方法，沿着X轴，Y轴或两者翻转UIImage。我不断接近，但我的变革知识不够好，得到所有的方式在那里。这是我到目前为止的代码：

I'm trying to create a method which flips a UIImage along the X axis, Y axis, or both. I keep getting close but my transform knowledge isn't good enough to get all the way there. Here is the code I have so far:

- (UIImage *)flippedImageByAxis:(MVImageFlip)axis{
     UIGraphicsBeginImageContext(self.size);
     CGContextRef context = UIGraphicsGetCurrentContext();
     CGAffineTransform verticalFlip = CGAffineTransformMake(1, 0, 0, -1, 0, self.size.height);
     CGAffineTransform horizFlip = CGAffineTransformMake(-1.0, 0.0, 0.0, 1.0, self.size.width, 0.0);

     if(axis == MVImageFlipXAxis || axis == MVImageFlipXAxisAndYAxis)
         CGContextConcatCTM(context, horizFlip);
     if(axis == MVImageFlipYAxis || axis == MVImageFlipXAxisAndYAxis)
         CGContextConcatCTM(context, verticalFlip);

     CGContextDrawImage(context, CGRectMake(0.0, 0.0, self.size.width, self.size.height), [self CGImage]);

     UIImage *flipedImage = UIGraphicsGetImageFromCurrentImageContext();
     UIGraphicsEndImageContext();

     return flipedImage;
 }

这会翻转图片，但是不正确。 Y翻转的图像根本不会被翻转，X翻转的图像看起来像XY图像应该看起来像，并且XY图像看起来像什么Y图像应该看起来像。组合转换并让它们正常工作正在使我的头部受伤。

This flips the image but not properly. The Y-flipped image doesn't get flipped at all, the X flipped image looks like the XY image should look like, and the XY image looks like what the Y image should look like. Combining the transforms and getting them to work properly is making my head hurt.

MVImageFlip枚举只是你在代码中看到的三个。没有什么特别的。

The MVImageFlip enum is just the three you see in the code. Nothing special.

推荐答案

我终于能够想出来。这里是适用于任何人可能需要它的代码。

I finally was able to figure this out. Here is the code that works for anyone else who might need it.

- (UIImage *)flippedImageByAxis:(MVImageFlip)axis{
    UIGraphicsBeginImageContext(self.size);
    CGContextRef context = UIGraphicsGetCurrentContext();

    if(axis == MVImageFlipXAxis){
        // Do nothing, X is flipped normally in a Core Graphics Context
    } else if(axis == MVImageFlipYAxis){
        // fix X axis
        CGContextTranslateCTM(context, 0, self.size.height);
        CGContextScaleCTM(context, 1.0f, -1.0f);

        // then flip Y axis
        CGContextTranslateCTM(context, self.size.width, 0);
        CGContextScaleCTM(context, -1.0f, 1.0f);
    } else if(axis == MVImageFlipXAxisAndYAxis){
        // just flip Y
        CGContextTranslateCTM(context, self.size.width, 0);
        CGContextScaleCTM(context, -1.0f, 1.0f);
    }

    CGContextDrawImage(context, CGRectMake(0.0, 0.0, self.size.width, self.size.height), [self CGImage]);

    UIImage *flipedImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return flipedImage;
}

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