ios - 在另存为 PNG 之前将新创建的 iOS 图像旋转 90 度

Question

我已经阅读了很多与此相关的答案，但我仍然无法让它工作。

我有一个 View ，用户可以在其中签名。它是这样的:http://d.pr/i/McuE

我可以成功检索此图像并将其保存到文件系统，但我需要在保存前将其旋转 90 度，以便签名从左到右读取。

// Grab the image
UIGraphicsBeginImageContext(self.signArea.bounds.size);
[self.signArea drawRect: self.signArea.bounds];
UIImage *signatureImage = UIGraphicsGetImageFromCurrentImageContext();

//-- ? -- Rotate the image (this doesn't work) -- ? --
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextRotateCTM(context, M_PI_2);

UIGraphicsEndImageContext();

//Save the image as a PNG in Documents folder
[UIImagePNGRepresentation(signatureImage) writeToFile:[[PPHelpers documentsPath] stringByAppendingPathComponent:@"signature-temp.png"] atomically:YES];

如何在保存前旋转图像？

在此先感谢您的帮助。我在 Xcode 5 上使用 iOS 7 SDK。

Answer 1

我终于使用这篇文章中的一个答案来解决这个问题:How to Rotate a UIImage 90 degrees?

我用的是这个方法:

- (UIImage *)imageRotatedByDegrees:(UIImage*)oldImage deg:(CGFloat)degrees{
  //Calculate the size of the rotated view's containing box for our drawing space
  UIView *rotatedViewBox = [[UIView alloc] initWithFrame:CGRectMake(0,0,oldImage.size.width, oldImage.size.height)];
  CGAffineTransform t = CGAffineTransformMakeRotation(degrees * M_PI / 180);
  rotatedViewBox.transform = t;
  CGSize rotatedSize = rotatedViewBox.frame.size;

  //Create the bitmap context
  UIGraphicsBeginImageContext(rotatedSize);
  CGContextRef bitmap = UIGraphicsGetCurrentContext();

  //Move the origin to the middle of the image so we will rotate and scale around the center.
  CGContextTranslateCTM(bitmap, rotatedSize.width/2, rotatedSize.height/2);

  //Rotate the image context
  CGContextRotateCTM(bitmap, (degrees * M_PI / 180));

  //Now, draw the rotated/scaled image into the context
  CGContextScaleCTM(bitmap, 1.0, -1.0);
  CGContextDrawImage(bitmap, CGRectMake(-oldImage.size.width / 2, -oldImage.size.height / 2, oldImage.size.width, oldImage.size.height), [oldImage CGImage]);

  UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();
  return newImage;
}

然后这样调用它:

//Rotate it
UIImage *rotatedImage = [self imageRotatedByDegrees:signatureImage deg:90];

谢谢大家。