比例和裁剪图像ios [英] scale and crop image ios

问题描述

我正在使用iOS的缩放和裁剪图像功能（类似于camara应用程序），下面的代码工作正常，只是结果图像出现了，我想了解原因。

I'm working in a function for scaling and crop image (similar to camara app) for iOS, the code below works fine, just that the resulting image came up side down, and I would like to understand why.

谢谢

- (UIImage*)imageByCropping:(UIImageView *)imageViewToCrop toRect:(CGRect)rect
{
    //create a context to do our clipping in
    CGRect newRect = CGRectApplyAffineTransform(rect, imageViewToCrop.transform);
    UIImage *imageToCrop = imageViewToCrop.image;
    UIGraphicsBeginImageContext(newRect.size);
    CGContextRef currentContext = UIGraphicsGetCurrentContext();

    //create a rect with the size we want to crop the image to
    //the X and Y here are zero so we start at the beginning of our
    //newly created context
    CGRect clippedRect = CGRectMake(0, 0, rect.size.width, rect.size.height);
    CGContextClipToRect( currentContext, clippedRect);


    //draw the image to our clipped context using our offset rect
    CGContextDrawImage(currentContext, newRect, imageToCrop.CGImage);

    //pull the image from our cropped context
    UIImage *cropped = UIGraphicsGetImageFromCurrentImageContext();

    //pop the context to get back to the default
    UIGraphicsEndImageContext();

    return cropped;

} 

推荐答案

我'我也没有解释就遇到过这个问题。但是找到了解决这个问题的解决方法。只需在代码中添加以下两行并再次尝试。它对我有用。

I've also came across this issue without explanation. But have found a workaround that solves that problem. Just put the following two lines in your code and try it again. It works for me.

CGContextTranslateCTM(context, 0.0, newRect.size.height);
CGContextScaleCTM(context, 1.0, -1.0);//flip context

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