c# - Winforms 应用程序中的填充橡皮筋

Question

如何在不透明度为 0.3 的窗体上绘制零不透明度橡皮筋？(橡皮筋是根据一个Microsoft的例子制作的

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更新:

我需要那个橡皮筋来起到像面具一样的作用。如果您使用 Jing 或任何其他屏幕截图工具，您将在尝试制作屏幕截图时准确地看到我需要做的事情:屏幕变为半透明，当您进行选择时，您将看到 0 不透明度选择

Answer 1

这就是您要找的机器人吗？

    public Form1()
    {
        InitializeComponent();
        DoubleBuffered = true;
    }

    bool mouseDown = false;
    Point mouseDownPoint = Point.Empty;
    Point mousePoint = Point.Empty;

    protected override void OnMouseDown(MouseEventArgs e)
    {
        base.OnMouseDown(e);
        mouseDown = true;
        mousePoint = mouseDownPoint = e.Location;
    }

    protected override void OnMouseUp(MouseEventArgs e)
    {
        base.OnMouseUp(e);
        mouseDown = false;
    }

    protected override void OnMouseMove(MouseEventArgs e)
    {
        base.OnMouseMove(e);
        mousePoint = e.Location;
        Invalidate();
    }

    protected override void OnPaint(PaintEventArgs e)
    {
        base.OnPaint(e);

        if (mouseDown)
        {
            Region r = new Region(this.ClientRectangle);
            Rectangle window = new Rectangle(
                Math.Min(mouseDownPoint.X, mousePoint.X),
                Math.Min(mouseDownPoint.Y, mousePoint.Y),
                Math.Abs(mouseDownPoint.X - mousePoint.X),
                Math.Abs(mouseDownPoint.Y - mousePoint.Y));
            r.Xor(window);
            e.Graphics.FillRegion(Brushes.Red, r);
            Console.WriteLine("Painted: " + window);
        }
    }