如何使用 CGContextAddLineToPoint 撤消画线？

Question

我正在为手绘开发一个画笔应用程序，我是核心图形框架的新手。

现在我的应用程序准备好仅使用以下代码进行绘图

override func touchesBegan(touches: NSSet!, withEvent event: UIEvent!)
{
    println("Enter in touchesBegan method");
    mouseSwiped = false;
    var touch : UITouch = touches.anyObject() as UITouch;
    lastPoint = touch.locationInView(self.view);
}

 override func touchesMoved(touches: NSSet!, withEvent event: UIEvent!)
{
    println("Enter in touchesMoved method");

    mouseSwiped = true;
    var touch : UITouch = touches.anyObject() as UITouch;
    var currentPoint : CGPoint = touch.locationInView(self.view);
    UIGraphicsBeginImageContext(self.view.frame.size);

    self.tempDrawImage!.image?.drawInRect(CGRect(x: 0, y: 0, width: self.view.frame.size.width, height: self.view.frame.size.height));

    println("lastPoint.X :\(lastPoint!.x) , lastPoint.Y :\(lastPoint!.y)")
    CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint!.x, lastPoint!.y);
    println("currentPoint.X :\(currentPoint.x) , currentPoint.Y :\(currentPoint.y)")
    CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
    CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
    CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), red!, green!, blue!, 1.0)
    CGContextSetLineWidth(UIGraphicsGetCurrentContext(), brush!);
    CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeNormal);
    CGContextStrokePath(UIGraphicsGetCurrentContext());

    //contexts!.addObject(UIGraphicsGetCurrentContext());


    self.tempDrawImage!.image = UIGraphicsGetImageFromCurrentImageContext();
    tempDrawImage!.alpha = opacity!;
    UIGraphicsEndImageContext();
    println("dot");
    lastPoint = currentPoint;
}

 override func touchesEnded(touches: NSSet!, withEvent event: UIEvent!)
{
    println("Enter in touchesEnded method");

    if mouseSwiped == false
    {
        println("false");
        UIGraphicsBeginImageContext(self.view.frame.size);

        self.tempDrawImage!.image?.drawInRect(CGRect(x: 0, y: 0, width: self.view.frame.size.width, height: self.view.frame.size.height));
        CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
        CGContextSetLineWidth(UIGraphicsGetCurrentContext(), brush!);
        CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), red!, green!, blue!, opacity!);
        CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint!.x, lastPoint!.y);
        CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), lastPoint!.x, lastPoint!.y);
        CGContextStrokePath(UIGraphicsGetCurrentContext())
        CGContextFlush(UIGraphicsGetCurrentContext());

        self.tempDrawImage!.image = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
    }

    UIGraphicsBeginImageContext(self.mainImage!.frame.size);

    self.mainImage!.image?.drawInRect(CGRect(x: 0, y: 0, width: self.view.frame.size.width, height: self.view.frame.size.height ), blendMode: kCGBlendModeNormal, alpha: 1.0);

    self.tempDrawImage!.image.drawInRect(CGRect(x: 0, y: 0, width: self.view.frame.width, height: self.view.frame.height), blendMode: kCGBlendModeNormal, alpha: opacity!);

    self.mainImage!.image = UIGraphicsGetImageFromCurrentImageContext();

    self.tempDrawImage!.image = nil

    UIGraphicsEndImageContext();
}

但在某些应用程序中，我看到它们在其应用程序中提供撤消功能，因此我也想提供此功能，如果使用绘制 2 行并按下撤消按钮，而不是最后添加的行从图像视图中一一删除

我对此进行了搜索，但我无法理解，并且没有一个答案被接受，所以我很困惑，所以请帮助我。

谢谢！

Answer 1

在您的情况下，因为您只添加行，这变得非常简单。您需要做的就是创建一个可变数组，该数组将包含来自用户输入的所有点。

现在，在每次触摸开始或最终将使用的任何内容时，您都将从代码中已有的点创建一个NSValue，并将此值添加到我之前提到的数组中。添加该行之后，您需要做的就是调用一些“刷新”方法，或者使用setNeedsDisplay 告诉视图重新显示，这将触发调用draw rect 方法。其余代码将从该方法中移出...

现在从撤消按钮的目标中，您将从数组中删除最后两个点（我希望这里没有问题）并调用刷新或重新显示（与触摸事件相同）。

因此，无论是将绘图代码移至“刷新”方法还是移至“绘制矩形”，您现在需要做的是首先清除上下文背景，然后遍历您的点数组并绘制每条线.

够简单吗？