旋转 CGImage答案

【问题标题】：Rotating a CGImage旋转 CGImage
【发布时间】：2012-05-19 16:02:12
【问题描述】：

我有一个从 UIImagePickerController 获取的 UIImage。当我从- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info 方法收到图像时，我将其直接放入 UIImageView 中进行预览，并为用户提供保存或丢弃图像的选项。

当用户选择保存选项时，应用程序会获取图像的 png 数据并将其保存到它的文档目录中。但是在两种可能的设备方向之一（仅限横向）下发生的情况是图像被颠倒保存（更具体地说，从它应该的位置旋转 180 度）。因此，当我在图库中加载图像时，它会出现颠倒。

（见图库左下角的图片）

我已经解决了这个问题，来自 UIImagePickerController 的 UIImage 中的原始图像数据不会旋转，而是将方向作为属性存储在对象上，并且仅在显示时应用。所以我正在尝试使用我在网上找到的一些代码来旋转与 UIImage 关联的 CGImage。但它似乎对图像完全没有影响。我使用的代码如下：

- (void)rotateImage:(UIImage*)image byRadians:(CGFloat)rads
{   
    // calculate the size of the rotated view's containing box for our drawing space 
    UIView *rotatedViewBox = [[UIView alloc] initWithFrame:CGRectMake(0,0,image.size.width, image.size.height)];
    CGAffineTransform t = CGAffineTransformMakeRotation(rads);
    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 you want to rotate and scale around the center. 
    CGContextTranslateCTM(bitmap, rotatedSize.width/2, rotatedSize.height/2); 

    // Rotate the image context
    CGContextRotateCTM(bitmap, rads);

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

    image = UIGraphicsGetImageFromCurrentImageContext();
    image = [UIImage imageWithCGImage:image.CGImage scale:1.0 orientation:UIImageOrientationDown];
    UIGraphicsEndImageContext();
}

我想知道为什么这段代码不起作用，因为我在网上找到的每段代码都可以进行图像旋转。

【问题讨论】：

标签： objective-c ios uiimage cgimage

【解决方案1】：

-(UIImage*) rotate:(UIImage*) src andOrientation:(UIImageOrientation)orientation
{
    UIGraphicsBeginImageContext(src.size);

    CGContextRef context=(UIGraphicsGetCurrentContext());

    if (orientation == UIImageOrientationRight) {
        CGContextRotateCTM (context, 90/180*M_PI) ;
    } else if (orientation == UIImageOrientationLeft) {
        CGContextRotateCTM (context, -90/180*M_PI);
    } else if (orientation == UIImageOrientationDown) {
        // NOTHING
    } else if (orientation == UIImageOrientationUp) {
        CGContextRotateCTM (context, 90/180*M_PI);
    }

    [src drawAtPoint:CGPointMake(0, 0)];
    UIImage *img=UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return img;

}

使用这个 .. 效果很好！当你从 UIImagePicker 中挑选图片时，请确保你使用了这个函数：

示例：

UIImage *image;
image = [self rotate:image andOrientation:image.imageOrientation];

确保在您从文档目录中选择照片的地方使用此功能。

【讨论】：

不错的答案...我唯一要改变的是“return img;”在“[img release];”之前被调用（这意味着发布调用从未真正命中）。此外，这假设此人未使用 ARC。
有人知道为什么需要轮换吗？

【解决方案2】：

我遇到了你的问题。你必须使用CGContextTranslateCTM(context, -rotatedSize.width/2, -rotatedSize.height/2); 将上下文翻译回来，并将绘图中的矩形原点设置为rotatedViewBox.frame.origin.x,rotatedViewBox.frame.origin.y。使用此代码。

UIView *rotatedViewBox = [[UIView alloc] initWithFrame:CGRectMake(0,0,image.size.width, image.size.height)];
CGAffineTransform t = CGAffineTransformMakeRotation(0.3);
rotatedViewBox.transform = t;
CGSize rotatedSize = rotatedViewBox.frame.size;



UIGraphicsBeginImageContext(rotatedSize);

CGContextRef context = UIGraphicsGetCurrentContext();
CGContextTranslateCTM(context, rotatedSize.width/2, rotatedSize.height/2);
CGContextRotateCTM (context, 0.3);
CGContextScaleCTM(context, 1, -1);
CGContextTranslateCTM(context, -rotatedSize.width/2, -rotatedSize.height/2);




CGContextDrawImage(context, CGRectMake(-rotatedViewBox.frame.origin.x, -rotatedViewBox.frame.origin.y, image.size.width, image.size.height), [image CGImage]);


UIImage *nn = UIGraphicsGetImageFromCurrentImageContext();

NSLog(@"size is %f, %f",nn.size.width,nn.size.height);
UIGraphicsEndImageContext();

UIImageWriteToSavedPhotosAlbum(nn, nil,nil,nil);

【讨论】：

【解决方案3】：

旋转和镜像 UIImage CGImage 支持数据 - Swift

我最近想更正由 CGImage 支持的 UIImage 以匹配所需的方向，而不是依赖 API 来尊重 UIImageOrientation 参数。

func createMatchingBackingDataWithImage(imageRef: CGImage?, orienation: UIImageOrientation) -> CGImage?
{
    var orientedImage: CGImage?

    if let imageRef = imageRef {
        let originalWidth = imageRef.width
        let originalHeight = imageRef.height
        let bitsPerComponent = imageRef.bitsPerComponent
        let bytesPerRow = imageRef.bytesPerRow

        let bitmapInfo = imageRef.bitmapInfo

        guard let colorSpace = imageRef.colorSpace else {
            return nil
        }

        var degreesToRotate: Double
        var swapWidthHeight: Bool
        var mirrored: Bool
        switch orienation {
        case .up:
            degreesToRotate = 0.0
            swapWidthHeight = false
            mirrored = false
            break
        case .upMirrored:
            degreesToRotate = 0.0
            swapWidthHeight = false
            mirrored = true
            break
        case .right:
            degreesToRotate = 90.0
            swapWidthHeight = true
            mirrored = false
            break
        case .rightMirrored:
            degreesToRotate = 90.0
            swapWidthHeight = true
            mirrored = true
            break
        case .down:
            degreesToRotate = 180.0
            swapWidthHeight = false
            mirrored = false
            break
        case .downMirrored:
            degreesToRotate = 180.0
            swapWidthHeight = false
            mirrored = true
            break
        case .left:
            degreesToRotate = -90.0
            swapWidthHeight = true
            mirrored = false
            break
        case .leftMirrored:
            degreesToRotate = -90.0
            swapWidthHeight = true
            mirrored = true
            break
        }
        let radians = degreesToRotate * Double.pi / 180.0

        var width: Int
        var height: Int
        if swapWidthHeight {
            width = originalHeight
            height = originalWidth
        } else {
            width = originalWidth
            height = originalHeight
        }

        let contextRef = CGContext(data: nil, width: width, height: height, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bitmapInfo.rawValue)
        contextRef?.translateBy(x: CGFloat(width) / 2.0, y: CGFloat(height) / 2.0)
        if mirrored {
            contextRef?.scaleBy(x: -1.0, y: 1.0)
        }
        contextRef?.rotate(by: CGFloat(radians))
        if swapWidthHeight {
            contextRef?.translateBy(x: -CGFloat(height) / 2.0, y: -CGFloat(width) / 2.0)
        } else {
            contextRef?.translateBy(x: -CGFloat(width) / 2.0, y: -CGFloat(height) / 2.0)
        }
        contextRef?.draw(imageRef, in: CGRect(x: 0.0, y: 0.0, width: CGFloat(originalWidth), height: CGFloat(originalHeight)))
        orientedImage = contextRef?.makeImage()
    }

    return orientedImage
}

【讨论】：

"您正在旋转上下文（及其坐标系），然后将图像绘制到其中。"出于这个原因，他们可以称上下文为画架，对吧？想知道为什么他们没有。理解什么是“画架”（毕竟大多数人都使用过）比理解什么是“上下文”更容易。
你的解决方案和Dream.In.Code的解决方案有什么区别？您正在考虑更多案例（例如镜像）。但还有什么？有些角度似乎不同，使用的方法也不同（CGContextRotateCTM vs.rotate）。你也在做一个translateBy，其他解决方案没有考虑到......
另外这个Gist有什么区别？

【解决方案4】：

Cameron Lowell Palmer answer 的 Swift 3 版本：

func createMatchingBackingDataWithImage(imageRef: CGImage?, orienation: UIImageOrientation) -> CGImage? {
    var orientedImage: CGImage?

    if let imageRef = imageRef {
        let originalWidth = imageRef.width
        let originalHeight = imageRef.height
        let bitsPerComponent = imageRef.bitsPerComponent
        let bytesPerRow = imageRef.bytesPerRow

        let colorSpace = imageRef.colorSpace
        let bitmapInfo = imageRef.bitmapInfo

        var degreesToRotate: Double
        var swapWidthHeight: Bool
        var mirrored: Bool
        switch orienation {
        case .up:
            degreesToRotate = 0.0
            swapWidthHeight = false
            mirrored = false
            break
        case .upMirrored:
            degreesToRotate = 0.0
            swapWidthHeight = false
            mirrored = true
            break
        case .right:
            degreesToRotate = 90.0
            swapWidthHeight = true
            mirrored = false
            break
        case .rightMirrored:
            degreesToRotate = 90.0
            swapWidthHeight = true
            mirrored = true
            break
        case .down:
            degreesToRotate = 180.0
            swapWidthHeight = false
            mirrored = false
            break
        case .downMirrored:
            degreesToRotate = 180.0
            swapWidthHeight = false
            mirrored = true
            break
        case .left:
            degreesToRotate = -90.0
            swapWidthHeight = true
            mirrored = false
            break
        case .leftMirrored:
            degreesToRotate = -90.0
            swapWidthHeight = true
            mirrored = true
            break
        }
        let radians = degreesToRotate * Double.pi / 180

        var width: Int
        var height: Int
        if swapWidthHeight {
            width = originalHeight
            height = originalWidth
        } else {
            width = originalWidth
            height = originalHeight
        }

        if let contextRef = CGContext(data: nil, width: width, height: height, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow, space: colorSpace!, bitmapInfo: bitmapInfo.rawValue) {

            contextRef.translateBy(x: CGFloat(width) / 2.0, y: CGFloat(height) / 2.0)
            if mirrored {
                contextRef.scaleBy(x: -1.0, y: 1.0)
            }
            contextRef.rotate(by: CGFloat(radians))
            if swapWidthHeight {
                contextRef.translateBy(x: -CGFloat(height) / 2.0, y: -CGFloat(width) / 2.0)
            } else {
                contextRef.translateBy(x: -CGFloat(width) / 2.0, y: -CGFloat(height) / 2.0)
            }
            contextRef.draw(imageRef, in: CGRect(x: 0, y: 0, width: originalWidth, height: originalHeight))

            orientedImage = contextRef.makeImage()
        }
    }

    return orientedImage
}

用法：

let newCgImage = createMatchingBackingDataWithImage(imageRef: cgImageRef, orienation: .left)

【讨论】：

【解决方案5】：

这只是对先前答案的重构。

func correctImageOrientation(cgImage: CGImage?, orienation: UIImage.Orientation) -> CGImage? {
    guard let cgImage = cgImage else { return nil }
    var orientedImage: CGImage?

    let originalWidth = cgImage.width
    let originalHeight = cgImage.height
    let bitsPerComponent = cgImage.bitsPerComponent
    let bytesPerRow = cgImage.bytesPerRow
    let bitmapInfo = cgImage.bitmapInfo

    guard let colorSpace = cgImage.colorSpace else { return nil }

    let degreesToRotate = orienation.getDegree()
    let mirrored = orienation.isMirror()

    var width = originalWidth
    var height = originalHeight

    let radians = degreesToRotate * Double.pi / 180.0
    let swapWidthHeight = Int(degreesToRotate / 90) % 2 != 0

    if swapWidthHeight {
        swap(&width, &height)
    }

    let context = CGContext(data: nil, width: width, height: height, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bitmapInfo.rawValue)

    context?.translateBy(x: CGFloat(width) / 2.0, y: CGFloat(height) / 2.0)
    if mirrored {
        context?.scaleBy(x: -1.0, y: 1.0)
    }
    context?.rotate(by: CGFloat(radians))
    if swapWidthHeight {
        swap(&width, &height)
    }
    context?.translateBy(x: -CGFloat(width) / 2.0, y: -CGFloat(height) / 2.0)

    context?.draw(cgImage, in: CGRect(x: 0.0, y: 0.0, width: CGFloat(originalWidth), height: CGFloat(originalHeight)))
    orientedImage = context?.makeImage()

    return orientedImage
}

extension UIImage.Orientation {
    func getDegree() -> Double {
        switch self {
        case .up, .upMirrored:
            return 0.0
        case .right, .rightMirrored:
            return 90.0
        case .down, .downMirrored:
            return 180.0
        case .left, .leftMirrored:
            return -90.0
        default:
            return 0
        }
    }

    func isMirror() -> Bool {
        switch self {
        case .up, .right, .down, .left:
            return false
        case .leftMirrored, .upMirrored, .downMirrored, .rightMirrored:
            return true
        default:
            return false
        }
    }
}

【讨论】：

【解决方案6】：

所有这些答案的问题在于它们具有 UIKit 依赖项。我正在开发面向 iOS 和 macOS 的 SwiftUI 通用应用程序。 Cameron Lowell Palmer answer 进行了一些修改：

bytesPerRow 计算需要在高度和宽度交换之后进行，否则 CGImageContext 抱怨不正确的 bytesPerRow
将 UIImageOrientation 更改为 CGImagePropertyOrientation，并交换左右旋转的符号

这是我的版本，适用于 iOS 和 macOS：

extension CGImage {
func rotating(to orientation: CGImagePropertyOrientation) -> CGImage? {
    var orientedImage: CGImage?

    let originalWidth = self.width
    let originalHeight = self.height
    let bitsPerComponent = self.bitsPerComponent
    let bitmapInfo = self.bitmapInfo

    guard let colorSpace = self.colorSpace else {
        return nil
    }

    var degreesToRotate: Double
    var swapWidthHeight: Bool
    var mirrored: Bool

    switch orientation {
    case .up:
        degreesToRotate = 0.0
        swapWidthHeight = false
        mirrored = false
        break
    case .upMirrored:
        degreesToRotate = 0.0
        swapWidthHeight = false
        mirrored = true
        break
    case .right:
        degreesToRotate = -90.0
        swapWidthHeight = true
        mirrored = false
        break
    case .rightMirrored:
        degreesToRotate = -90.0
        swapWidthHeight = true
        mirrored = true
        break
    case .down:
        degreesToRotate = 180.0
        swapWidthHeight = false
        mirrored = false
        break
    case .downMirrored:
        degreesToRotate = 180.0
        swapWidthHeight = false
        mirrored = true
        break
    case .left:
        degreesToRotate = 90.0
        swapWidthHeight = true
        mirrored = false
        break
    case .leftMirrored:
        degreesToRotate = 90.0
        swapWidthHeight = true
        mirrored = true
        break
    }

    let radians = degreesToRotate * Double.pi / 180.0

    var width: Int
    var height: Int

    if swapWidthHeight {
        width = originalHeight
        height = originalWidth
    } else {
        width = originalWidth
        height = originalHeight
    }

    let bytesPerRow = (width * bitsPerPixel) / 8

    let contextRef = CGContext(data: nil, width: width, height: height, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bitmapInfo.rawValue)

    contextRef?.translateBy(x: CGFloat(width) / 2.0, y: CGFloat(height) / 2.0)

    if mirrored {
        contextRef?.scaleBy(x: -1.0, y: 1.0)
    }

    contextRef?.rotate(by: CGFloat(radians))

    if swapWidthHeight {
        contextRef?.translateBy(x: -CGFloat(height) / 2.0, y: -CGFloat(width) / 2.0)
    } else {
        contextRef?.translateBy(x: -CGFloat(width) / 2.0, y: -CGFloat(height) / 2.0)
    }

    contextRef?.draw(self, in: CGRect(x: 0.0, y: 0.0, width: CGFloat(originalWidth), height: CGFloat(originalHeight)))

    orientedImage = contextRef?.makeImage()

    return orientedImage
}

}

【讨论】：