ios - 图像旋转会导致像素丢失吗？(Core Graphics)

Question

我正在尝试在我的代码中实现图像旋转并运行几个测试。由于我不太了解如何执行旋转的数学知识，因此我只是按照我在 Internet 上找到的一些说明并实现了我的代码。

我发现每次旋转图像时，边缘周围的整行或整列 1 像素都会丢失。 (一次超过M_PI学位)

当我将图像托管为 UIImage 对象时，这并不明显，但是当您将 UIImage 另存为文件时，您可以看到它。

这是我的测试代码链接: https://github.com/asldkfjwoierjlk/UIImageRotationTest/tree/master

我不明白这种损失会发生。我错过了什么？或者它在数学上是不可避免的？

如果您有兴趣，这是我实现的旋转方法。

- (UIImage*)rotateImg:(UIImage*)srcImg
{
    UIView *rotatedViewBox = [[UIView alloc] initWithFrame:CGRectMake(0,0, srcImg.size.width, srcImg.size.height)];
CGFloat rotationInDegree = ROTATION_DEGREE;

CGAffineTransform t = CGAffineTransformMakeRotation(rotationInDegree);
rotatedViewBox.transform = t;
CGSize rotatedSize = rotatedViewBox.frame.size;


// set opaque option to NO to leave the alpha channel intact.
// Otherwise, there's no point of saving to either png or jpg.
UIGraphicsBeginImageContextWithOptions(rotatedSize, NO, 1.0);

CGContextRef context = UIGraphicsGetCurrentContext();
CGContextTranslateCTM(context, rotatedSize.width / 2.0f, rotatedSize.height / 2.0f);
CGContextRotateCTM(context, rotationInDegree);
[srcImg drawInRect:CGRectMake(-srcImg.size.width / 2.0f, -srcImg.size.height / 2.0f, srcImg.size.width, srcImg.size.height)];

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


return newImage;
}

Answer 1

您可以将 UIImageView 作为 View 来处理。这段代码非常适合我!

 CABasicAnimation *rotationAnimation = [CABasicAnimation animationWithKeyPath:@"transform.rotation.z"];
NSNumber *currentAngle = [rotatedViewBox.layer.presentationLayer valueForKeyPath:@"transform.rotation"];
rotationAnimation.fromValue = currentAngle;
rotationAnimation.toValue = @(50*M_PI);
rotationAnimation.duration = 50.0f;             // this might be too fast
rotationAnimation.repeatCount = HUGE_VALF;     // HUGE_VALF is defined in math.h so import it
[rotatedViewBox.layer addAnimation:rotationAnimation forKey:@"rotationAnimationleft"];

编码愉快!