c# - 如何使用 MouseMove 事件绘制单线

Question

我正在尝试使用 OnMouseMove() 事件绘制一条直线。我的问题是每次我移动鼠标时它都会留下痕迹。我尝试使用刷新方法，但是当我停止移动鼠标时，该行就消失了。我不想画线OnPaint();，只想画线OnMouseMove()。

编辑: 我使用的是透明面板(cp.ExStyle |= 0x20;)，所以我不能使用 graphics.Clear() 和 背景颜色()

这是一个没有 Refresh() 的示例图像:

这是我的代码:

private void panel1_MouseMove(object sender, MouseEventArgs e)
{  
   Graphics g = panel1.CreateGraphics();

   g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
   using (var p = new Pen(Color.Black, 3))
   {
      p.StartCap = System.Drawing.Drawing2D.LineCap.ArrowAnchor;
      p.EndCap = System.Drawing.Drawing2D.LineCap.ArrowAnchor;

      g.DrawLine(p, st, e.Location);
   }
   Thread.Sleep(30);
   Invalidate();
   //this.Refresh();

   g.Dispose();
}

问候

Answer 1

以下对我有用。基本上跟踪最后绘制的线条并使用面板的背景颜色绘制它(给出清除它的效果)。

   public partial class Form1 : Form
   {
      public Form1()
      {
         InitializeComponent();
      }

      private const int PEN_WIDTH = 3;
      private const LineCap START_CAP = LineCap.ArrowAnchor;
      private const LineCap END_CAP = LineCap.ArrowAnchor;
      Point mAnchorPoint = new Point(10, 10);
      Point mPreviousPoint = Point.Empty;

      private void panel1_MouseMove(object sender, MouseEventArgs e)
      {
         using (Graphics g = panel1.CreateGraphics())
         {
            // Clear last line drawn
            using (Pen clear_pen = new Pen(panel1.BackColor, PEN_WIDTH))
            {
               clear_pen.StartCap = START_CAP;
               clear_pen.EndCap = END_CAP;
               g.DrawLine(clear_pen, mAnchorPoint, mPreviousPoint);
            }

            // Update previous point
            mPreviousPoint = e.Location;

            // Draw the new line
            using (Pen draw_pen = new Pen(Color.Black, PEN_WIDTH))
            {
               draw_pen.StartCap = START_CAP;
               draw_pen.EndCap = END_CAP;
               g.DrawLine(draw_pen, mAnchorPoint, e.Location);
            }
         }
      }
   }

如果面板的背景颜色设置为透明，则需要将 panel1.BackColor 更改为 panel1.Parent.BackColor

如果透明面板不起作用，您可以使用 DrawReversibleLine 函数(虽然这不允许更改线条的颜色或粗细，但绘图应该没有问题/即使面板是透明的也删除:

  Point mAnchorPoint = new Point(200, 200);
  Point mPreviousPoint = Point.Empty;

  private void panel1_MouseMove(object sender, MouseEventArgs e)
  {
     if (mPreviousPoint != Point.Empty)
     {
        // Clear last line drawn
        ControlPaint.DrawReversibleLine(PointToScreen(mAnchorPoint), PointToScreen(mPreviousPoint), Color.Pink);
     }

     // Update previous point
     mPreviousPoint = e.Location;
     mPreviousPoint.Offset(myPanel1.Location);

     // Draw the new line
     ControlPaint.DrawReversibleLine(PointToScreen(mAnchorPoint), PointToScreen(mPreviousPoint), Color.Pink);
  }