从旋转的 UIImageView 创建 UIImage

Question

我有一个 UIImageView，里面有一张图片。我通过将 UIImageView 的变换属性设置为 CGAffineTransformMakeRotation(angle) 在显示之前旋转了图像，其中角度是以弧度为单位的角度。

我希望能够创建另一个与我在视图中看到的旋转版本相对应的 UIImage。

我快到了，通过旋转图像上下文，我得到一个旋转的图像：

- (UIImage *) rotatedImageFromImageView: (UIImageView *) imageView
{
    UIImage *rotatedImage;

    // Get image width, height of the bounding rectangle
    CGRect boundingRect = [self getBoundingRectAfterRotation: imageView.bounds byAngle:angle];

    // Create a graphics context the size of the bounding rectangle
    UIGraphicsBeginImageContext(boundingRect.size);
    CGContextRef context = UIGraphicsGetCurrentContext();

    // Rotate and translate the context
    CGAffineTransform ourTransform = CGAffineTransformIdentity;
    ourTransform = CGAffineTransformConcat(ourTransform, CGAffineTransformMakeRotation(angle));

    CGContextConcatCTM(context, ourTransform);

    // Draw the image into the context
    CGContextDrawImage(context, CGRectMake(0, 0, imageView.image.size.width, imageView.image.size.height), imageView.image.CGImage);

    // Get an image from the context
    rotatedImage = [UIImage imageWithCGImage: CGBitmapContextCreateImage(context)];

    // Clean up
    UIGraphicsEndImageContext();
    return rotatedImage;
 }

但是，图像并未围绕其中心旋转。我尝试了各种与我的旋转连接的变换，以使其围绕中心旋转，但无济于事。我错过了一个技巧吗？这是否可能，因为我正在旋转上下文而不是图像？

现在急于完成这项工作，因此我们将不胜感激。

戴夫

编辑：我的boundingRect代码已经被问过好几次了，所以这里是：

- (CGRect) getBoundingRectAfterRotation: (CGRect) rectangle byAngle: (CGFloat) angleOfRotation {
    // Calculate the width and height of the bounding rectangle using basic trig
    CGFloat newWidth = rectangle.size.width * fabs(cosf(angleOfRotation)) + rectangle.size.height * fabs(sinf(angleOfRotation));
    CGFloat newHeight = rectangle.size.height * fabs(cosf(angleOfRotation)) + rectangle.size.width * fabs(sinf(angleOfRotation));

    // Calculate the position of the origin
    CGFloat newX = rectangle.origin.x + ((rectangle.size.width - newWidth) / 2);
    CGFloat newY = rectangle.origin.y + ((rectangle.size.height - newHeight) / 2);

    // Return the rectangle
    return CGRectMake(newX, newY, newWidth, newHeight);
}

Answer 1

好的——我似乎终于做到了。任何关于正确性的 cmets 都会很有用……需要平移、旋转、缩放和从绘图矩形位置偏移才能使其工作。代码在这里：

CGAffineTransform transform = CGAffineTransformIdentity;
transform = CGAffineTransformTranslate(transform, boundingRect.size.width/2, boundingRect.size.height/2);
transform = CGAffineTransformRotate(transform, angle);
transform = CGAffineTransformScale(transform, 1.0, -1.0);

CGContextConcatCTM(context, transform);

// Draw the image into the context
CGContextDrawImage(context, CGRectMake(-imageView.image.size.width/2, -imageView.image.size.height/2, imageView.image.size.width, imageView.image.size.height), imageView.image.CGImage);

// Get an image from the context
rotatedImage = [UIImage imageWithCGImage: CGBitmapContextCreateImage(context)];