gdi+画直线去重影
部分代码
bool isok=false
point startP,endP
Pen p;

鼠标按下事件函数
startP.x=e.x
startP.y=e.y
isok=true

鼠标移到时间函数
if(isok)
{
endP.x=e.x
endP.y=e.y
Graphics g=this.CreateGraphics()
g.DrawLine(p,startP,endP);
}

鼠标松开事件函数

isok=false




这样画的结果是有重影，请问怎么去掉重影？

[解决办法]
if(isok)
{
this.Refresh(); //清除以前画的线
endP.X=e.X;
endP.Y=e.Y ;
Graphics g = this.CreateGraphics();
g.DrawLine(p,startP,endP);
}
[解决办法]
if (e.Button == MouseButtons.Left)
{
// 第一个 DrawReversible 为消除原来的辅助线
// 第二个 DrawReversible 画新的辅助线
if (rbLine.Checked)
{
ControlPaint.DrawReversibleLine(this.PointToScreen(ps), this.PointToScreen(pe), Color.Black);
pe = e.Location;
ControlPaint.DrawReversibleLine(this.PointToScreen(ps), this.PointToScreen(pe), Color.Black);
}
else
{
ControlPaint.DrawReversibleFrame(this.RectangleToScreen(SelectRect), Color.Black, FrameStyle.Dashed);
SelectRect.Width = e.X - SelectRect.X;
SelectRect.Height = e.Y - SelectRect.Y;
ControlPaint.DrawReversibleFrame(this.RectangleToScreen(SelectRect), Color.Black, FrameStyle.Dashed);
}
[解决办法]
把你画好的线记住，在onpaint事件里将这些线画出来．



bool isok=false ;
Point startP, endP;
Pen p=Pens.Black;

private void Form1_MouseDown(object sender, MouseEventArgs e)
{
startP.X=e.X ;
startP.Y=e.Y ;
isok = true;

}

private void Form1_MouseMove(object sender, MouseEventArgs e)
{
if(isok)
{
this.Refresh();
endP.X=e.X;
endP.Y=e.Y ;
Graphics g = this.CreateGraphics();
g.DrawLine(p,startP,endP);
}
}



List<Point> sP = new List<Point>();
List<Point> eP = new List<Point>();
private void Form1_MouseUp(object sender, MouseEventArgs e)
{
isok = false;
sP.Add(startP);
eP.Add(e.Location);
}

private void Form1_Paint(object sender, PaintEventArgs e)
{
for (int i = 0; i < sP.Count; i++)
{
e.Graphics.DrawLine(p, sP[i],eP[i]);
}
}
[解决办法]

C# code

public partial class Form1 : Form 
 { 
   Boolean bHaveMouse; 
   Point ptOriginal = new Point(); 
   Point ptLast = new Point(); 
  
   // Called when the left mouse button is pressed.  
   public void MyMouseDown(Object sender, MouseEventArgs e) 
   { 
     // Make a note that we "have the mouse". 
     bHaveMouse = true; 
     // Store the "starting point" for this rubber-band rectangle. 
     ptOriginal.X = e.X; 
     ptOriginal.Y = e.Y; 
     // Special value lets us know that no previous 
     // rectangle needs to be erased.  
 
     ptLast.X = -1; 
     ptLast.Y = -1; 
   } 
   // Convert and normalize the points and draw the reversible frame. 
   private void MyDrawReversibleLine(Point p1, Point p2) 
   { 
     // Convert the points to screen coordinates. 
     p1 = PointToScreen(p1); 
     p2 = PointToScreen(p2); 
     ControlPaint.DrawReversibleLine(p1, p2, Color.Red); 
   } 
   // Called when the left mouse button is released. 
   public void MyMouseUp(Object sender, MouseEventArgs e) 
   { 
     // Set internal flag to know we no longer "have the mouse". 
     bHaveMouse = false; 
     // If we have drawn previously, draw again in that spot 
     // to remove the lines. 
     if (ptLast.X != -1) 
     { 
       Point ptCurrent = new Point(e.X, e.Y); 
     } 
  
     Graphics g = this.CreateGraphics(); 
     Pen pen = new Pen(System.Drawing.Color.Black); 
  
     g.DrawLine(pen, ptOriginal, ptLast); 
  
     pen.Dispose(); 
     g.Dispose(); 
  
  
     // Set flags to know that there is no "previous" line to reverse. 
     ptLast.X = -1; 
     ptLast.Y = -1; 
     ptOriginal.X = -1; 
     ptOriginal.Y = -1; 
   } 
   // Called when the mouse is moved. 
   public void MyMouseMove(Object sender, MouseEventArgs e) 
   { 
     Point ptCurrent = new Point(e.X, e.Y); 
     // If we "have the mouse", then we draw our lines. 
     if (bHaveMouse) 
     { 
       // If we have drawn previously, draw again in 
       // that spot to remove the lines. 
       if (ptLast.X != -1) 
       { 
         MyDrawReversibleLine(ptOriginal, ptLast); 
       } 
       // Update last point. 
       ptLast = ptCurrent; 
       // Draw new lines. 
       MyDrawReversibleLine(ptOriginal, ptCurrent); 
     } 
   } 
   // Set up delegates for mouse events. 
   protected override void OnLoad(System.EventArgs e) 
   { 
     this.Width = 800; 
     this.Height = 600; 
     MouseDown += new MouseEventHandler(MyMouseDown); 
     MouseUp += new MouseEventHandler(MyMouseUp); 
     MouseMove += new MouseEventHandler(MyMouseMove); 
     bHaveMouse = false; 
   } 
  
 }