Question

我尝试使用裁剪框UIImage裁剪UIView，用户可以在图片视图中的任意位置拖动以进行裁剪。我用来计算裁剪矩形的逻辑如下：

 extension UIImageView {

    public func computeCropRect(for sourceFrame : CGRect) -> CGRect {

        let widthScale = bounds.size.width / image!.size.width
        let heightScale = bounds.size.height / image!.size.height

        var x : CGFloat = 0
        var y : CGFloat = 0
        var width : CGFloat = 0
        var height : CGFloat = 0
        var offSet : CGFloat = 0

        if widthScale < heightScale {
            offSet = (bounds.size.height - (image!.size.height * widthScale))/2
            x = sourceFrame.origin.x / widthScale
            y = (sourceFrame.origin.y - offSet) / widthScale
            width = sourceFrame.size.width / widthScale
            height = sourceFrame.size.height / widthScale
        } else {
            offSet = (bounds.size.width - (image!.size.width * heightScale))/2
            x = (sourceFrame.origin.x - offSet) / heightScale
            y = sourceFrame.origin.y / heightScale
            width = sourceFrame.size.width / heightScale
            height = sourceFrame.size.height / heightScale
        }

        return CGRect(x: x, y: y, width: width, height: height)
    }
}

裁剪框框架看起来像这样，可以通过拖动它定位在图像视图框架的任何位置：

这个裁剪代码工作正常，直到我将其与另一个功能结合起来我试图支持哪个能够让用户在UIImageView内使用他们的手指进行绘制。代码如下：

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

            if let touchPoint = touches.first {

                let currentPoint = touchPoint.location(in: self)

                 UIGraphicsBeginImageContextWithOptions(frame.size, false, UIScreen.main.scale)

                if let context = UIGraphicsGetCurrentContext() {

                    image?.draw(in: imageEffectsService.computeAspectFitFrameFor(containerSize: frame.size, imageSize: image!.size), blendMode: .normal, alpha: CGFloat(imageOpacity))

                    drawLineAt(startPoint: lastTouchPoint, endPoint: currentPoint, currentContext: context, strokeColor: drawColor)

                    UIGraphicsEndImageContext() 
                }
            }
    }  


private func drawLineAt(startPoint : CGPoint, endPoint : CGPoint, currentContext : CGContext, strokeColor : UIColor) {

        currentContext.beginPath()
        currentContext.setLineCap(CGLineCap.round)
        currentContext.setLineWidth(brushSize)
        currentContext.setStrokeColor(strokeColor.cgColor)
        currentContext.move(to: startPoint)
        currentContext.addLine(to: endPoint)
        currentContext.strokePath()

        image = UIGraphicsGetImageFromCurrentImageContext()
    }

一旦我应用绘图，裁剪方法就会失去准确性，特别是因为这一行：

UIGraphicsBeginImageContextWithOptions(frame.size, false, UIScreen.main.scale)

如果我使用：

UIGraphicsBeginImageContext(frame.size)

我的裁剪代码将是准确的，但绘图保真度将看起来颗粒状和低质量，因为我不考虑视网膜屏幕设备。我的问题是如何修改我的裁剪功能以考虑UIScreen.main.scale？

如何考虑屏幕比例裁剪UIImage

0 个答案: