UIGraphicsGetImageFromCurrentContext 并保持纵横比

Question

我正在尝试实现一个UIImageView 子类，它允许用户用手指在图像视图中绘图。我的UIImageView 的 contentMode 设置为Aspect Fill。我注意到，当我的绘图代码执行并从图形上下文中提取生成的图像时，它正在以Scale to Fill 类型格式进行缩放，这不是我想要的。我想知道是否有人知道如何实现提取此图像并保持图像的纵横比。

class DrawImageView : UIImageView {

    var lastTouchPoint = CGPoint.zero
    var isSwiping = false

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        isSwiping = false 
        if let touchPoint = touches.first {
            lastTouchPoint = touchPoint.location(in: self)
        }
    }

    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        isSwiping = true

        if let touchPoint = touches.first {
            let currentPoint = touchPoint.location(in: self)
            UIGraphicsBeginImageContext(frame.size)

            image?.draw(in: CGRect(x:0, y:0, width:frame.size.width, height:frame.size.height))

            if let context = UIGraphicsGetCurrentContext() {
                context.move(to: lastTouchPoint)
                context.addLine(to: currentPoint)
                context.setLineCap(CGLineCap.round)
                context.setLineWidth(9.0)
                context.setStrokeColor(red: 0/255.0, green: 0/255.0, blue: 0/255.0, alpha: 1.0)
                context.strokePath()
                image = UIGraphicsGetImageFromCurrentImageContext()
                UIGraphicsEndImageContext()
                lastTouchPoint = currentPoint
            }
        }
    }

    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        if(!isSwiping) {

            UIGraphicsBeginImageContext(frame.size)
            image?.draw(in: CGRect(x:0, y:0, width:frame.size.width, height:frame.size.height))


            if let context = UIGraphicsGetCurrentContext() {
                context.setLineCap(CGLineCap.round)
                context.setLineWidth(9.0)
                context.setStrokeColor(red: 0/255.0, green: 0/255.0, blue: 0/255.0, alpha: 1.0)
                context.move(to: lastTouchPoint)
                context.addLine(to: lastTouchPoint)
                context.strokePath()
                image = UIGraphicsGetImageFromCurrentImageContext()
                UIGraphicsEndImageContext()
            }
        }
    }
}

Answer 1

使用此代码：

UIGraphicsBeginImageContext(frame.size)
image?.draw(in: CGRect(x:0, y:0, width:frame.size.width, height:frame.size.height))

您是在说“将这张完整的图像 - 无论大小或纵横比 - 绘制成一个宽 x 高尺寸的矩形。”因此，如果 image 的“原始”大小为 300 x 200，而您的 frame 为 200 x 200，那么这就是要绘制图像的位置。

为避免这种情况，您需要计算要绘制的正确矩形。使用这些尺寸，你会想要做（用于方面填充）：

image?.draw(in: CGRect(x:-50, y:0, width:frame.size.width + 50, height:frame.size.height))

当然，您可以运行快速计算来确定实际数字，而不是硬编码值。

Answer 2

我最终发现并用于提供方面填充矩形和方面适合矩形的函数如下：

 func getAspectFillFrame(sizeImageView : CGSize, sizeImage: CGSize) -> CGRect {

        let aspect = sizeImage.width / sizeImage.height
        let rect: CGRect

        if sizeImageView.width / aspect > sizeImageView.height {

            let height = sizeImageView.width / aspect

            rect = CGRect(x: 0, y: (sizeImageView.height - height) / 2,
                          width: sizeImageView.width, height: height)

        } else {
            let width = sizeImageView.height * aspect
            rect = CGRect(x: (sizeImageView.width - width) / 2, y: 0,
                          width: width, height: sizeImageView.height)
        }

        return rect

    }

    func getAspectFitFrame(sizeImgView:CGSize, sizeImage:CGSize) -> CGRect {

        let imageSize:CGSize  = sizeImage
        let viewSize:CGSize = sizeImgView

        let hfactor : CGFloat = imageSize.width/viewSize.width
        let vfactor : CGFloat = imageSize.height/viewSize.height

        let factor : CGFloat = max(hfactor, vfactor)

        // Divide the size by the greater of the vertical or horizontal shrinkage factor
        let newWidth : CGFloat = imageSize.width / factor
        let newHeight : CGFloat = imageSize.height / factor

        var x:CGFloat = 0.0
        var y:CGFloat = 0.0
        if newWidth > newHeight{
            y = (sizeImgView.height - newHeight)/2
        }
        if newHeight > newWidth{
            x = (sizeImgView.width - newWidth)/2
        }
        let newRect:CGRect = CGRect(x: x, y: y, width: newWidth, height: newHeight)

        return newRect

    }