在 UISplitViewController 中绘图的奇怪错误

Question

我正在尝试制作具有用户可以在其中绘制内容的视图的屏幕。我用这样的代码创建了自定义视图：

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    swiped = false
    if let touch = touches.first {
        lastPoint = touch.location(in: imageView)
    }
}

override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
    swiped = true
    if let touch = touches.first {
        let currentPoint = touch.location(in: imageView)
        drawLine(fromPoint: lastPoint, toPoint: currentPoint)

        lastPoint = currentPoint
    }
}

override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
    if !swiped {
        // draw a single point
        drawLine(fromPoint: lastPoint, toPoint: lastPoint)
    }

和绘图功能

func drawLine(fromPoint: CGPoint, toPoint: CGPoint) {
    UIGraphicsBeginImageContext(imageView.frame.size)
    let context = UIGraphicsGetCurrentContext()
    imageView.image?.draw(in: CGRect(x: 0, y: 0, width: imageView.frame.size.width, height: imageView.frame.size.height))

    context?.move(to: fromPoint)
    context?.addLine(to: toPoint)

    context?.setLineCap(.round)
    context?.setLineWidth(lineWidth)
    context?.setStrokeColor(lineColor.cgColor)

    context?.strokePath()

    imageView.image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
}

当我在视图控制器中显示该视图时一切正常：

但是当我在 UISplitViewController 的详细视图中显示它时，当用户继续绘制时，已经绘制的图像的一部分移动并淡出：

我找不到任何关于网络错误的信息，也不知道是什么导致了这种行为

有人对此有什么想法吗？

这是一个示例项目，您可以在其中重现该错误： https://github.com/fizzy871/DrawingBug

顺便说一句，在实际项目中，不仅分视图控制器的主视图，而且导航栏也会影响绘图

Answer 1

事实证明，由于 imageView 框架的尺寸有小数部分，所以它会这样。

我刚刚将绘图上下文乘以 2，问题就解决了：

func drawLine(fromPoint fromPoint: CGPoint, toPoint: CGPoint) {
    // multiply to avoid problems when imageView frame value is XX.5
    let fixedFrameForDrawing = CGRect(x: 0, y: 0, width: imageView.frame.size.width*2, height: imageView.frame.size.height*2)
    let point1 = CGPoint(x: fromPoint.x*2, y: fromPoint.y*2)
    let point2 = CGPoint(x: toPoint.x*2, y: toPoint.y*2)
    UIGraphicsBeginImageContext(fixedFrameForDrawing.size)
    if let context = UIGraphicsGetCurrentContext() {
        imageView.image?.draw(in: fixedFrameForDrawing)

        context.move(to: point1)
        context.addLine(to: point2)

        context.setLineCap(.round)
        context.setLineWidth(lineWidth*2)
        context.setStrokeColor(lineColor.cgColor)

        context.strokePath()

        let imageFromContext = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        imageView.image = imageFromContext
    }

在 UISplitViewController 中绘图的奇怪错误

strange bug with drawing in UISplitViewController

drawing

core-graphics

uinavigationbar

swift

uistackview