gdi+画直线去重影

Question

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？

Answer 1

 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); 
            }

Answer 2

 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);
                }

Answer 3

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]);
            }
        }

Answer 4

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;
    }}