Question

我当前的程序允许用户单击一个点，然后单击另一个点（至少20个像素）并在这两个点之间画一条线。我使用过折线，这样可以多次完成。虽然所有行的集合仅在完成所有点击后出现。

void DrawingCanvas_MouseUp(object sender, MouseButtonEventArgs e) {
        Point position = e.GetPosition(this);

        if (leftList == null) {
            //starting a new set
            leftList.Add(position);
            lastPoint = position;
            return;
        }
        //calculate distance, i.e. end click
        double a = lastPoint.X - position.X;
        double b = lastPoint.Y - position.Y;
        double distance = Math.Sqrt(a * a + b * b);
        if (distance > 20) {
            //continue to add to list
            leftList.Add(position);
            lastPoint = position;
        } else {
            //end of the line
            paint();
            leftList = new PointCollection(); 
        }

    }

    private void paint() {
        Polyline line = new Polyline();
        line.Visibility = System.Windows.Visibility.Visible;
        line.StrokeThickness = 2;
        line.Stroke = System.Windows.Media.Brushes.Black;
        line.Points = leftList;
        myCanvas.Children.Add(line);
    }

所以我的问题是双重的：

A）如何制作，以便每次点击后立即添加新行。

B）如何在最后一个点和鼠标光标当前位置之间（即在您选择下一个点之前）之间渲染一条线

Answer 1

以下简单示例在按下鼠标左键并且鼠标移动最小点距离20并且按下按钮时开始绘制新的折线。它以红色或绿色绘制最后一条折线段（到当前鼠标位置），具体取决于其长度。如果释放鼠标按钮并且新片段的长度>> 20，则将新点附加到折线。否则，折线终止，并且可以创建新的折线。

private Polyline polyline;
private Polyline segment = new Polyline { StrokeThickness = 2 };

private void Canvas_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
    if (polyline == null)
    {
        var canvas = (Canvas)sender;
        var point = e.GetPosition(canvas);

        // create new polyline
        polyline = new Polyline { Stroke = Brushes.Black, StrokeThickness = 2 };
        polyline.Points.Add(point);
        canvas.Children.Add(polyline);

        // initialize current polyline segment
        segment.Stroke = Brushes.Red;
        segment.Points.Add(point);
        segment.Points.Add(point);
        canvas.Children.Add(segment);
    }
}

private void Canvas_MouseMove(object sender, MouseEventArgs e)
{
    if (polyline != null)
    {
        // update current polyline segment
        var canvas = (Canvas)sender;
        segment.Points[1] = e.GetPosition(canvas);

        var distance = (segment.Points[0] - segment.Points[1]).Length;
        segment.Stroke = distance >= 20 ? Brushes.Green : Brushes.Red;
    }
}

private void Canvas_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
{
    if (polyline != null)
    {
        var canvas = (Canvas)sender;
        segment.Points[1] = e.GetPosition(canvas);

        var distance = (segment.Points[0] - segment.Points[1]).Length;

        if (distance >= 20)
        {
            polyline.Points.Add(segment.Points[1]);
            segment.Points[0] = segment.Points[1];
        }
        else
        {
            if (polyline.Points.Count < 2)
            {
                canvas.Children.Remove(polyline);
            }

            polyline = null;
            segment.Points.Clear();
            canvas.Children.Remove(segment);
        }
    }
}

Answer 2

请在每次点击时保留一系列积分。在集合中，您可以添加一个类，它将具有两个属性，如StartPoint和EndPoint。

第一次单击鼠标时，只需将一个类对象添加到仅具有起点的集合中。当您下次单击鼠标时，广告结束指向该类的最后一个对象，同时创建一个新对象并将此点指定为其起点，并在调用绘制函数后将其添加到集合中。

实时绘制线到下一个点

2 个答案: