BitMap背景色问题
为什么bitmap类型的变量没有设置背景色时，画图是会产生重影？

下面为代码 发表于：2009-02-02 21:25:01 楼主 
/* 
* Created by SharpDevelop. 
* User: Administrator 
* Date: 2009-2-2 
* Time: 20:26 
* 
* To change this template use Tools | Options | Coding | Edit Standard Headers. 
*/ 
using System; 
using System.Drawing; 
using System.Windows.Forms; 

namespace DrawG 
{ 
/// <summary> 
/// Description of Box2. 
/// </summary> 
public partial class Box2 : Form 
{ 

protected Image imgPic; 
protected Point pS,pE; 
protected Graphics temG; 
protected Image imgTem; 
protected Pen p; 
protected bool flag=false ; 


public Box2() 
{ 
// 
// The InitializeComponent() call is required for Windows Forms designer support. 
// 
InitializeComponent(); 
p=new Pen (Color.Blue ,2); 
imgPic =new Bitmap (pbImg .Width ,pbImg .Height ); 
imgTem =(Image )imgPic.Clone () ; 

// 
// TODO: Add constructor code after the InitializeComponent() call. 
// 
} 

void PbImgMouseDown(object sender, MouseEventArgs e) 
{ 
pS =new Point (e.X ,e.Y ); 
flag =true ; 
} 

void PbImgMouseMove(object sender, MouseEventArgs e) 
{ 
if (flag ) 
{ 
pE =new Point (e.X,e.Y ); 
Image img=(Image )imgPic .Clone (); 
temG =Graphics .FromImage (img ); 
temG .DrawLine (p,pS ,pE ); 
temG .Dispose (); 
temG =Graphics .FromImage (imgTem ); 
temG .DrawImage (img,0,0); 
temG .Dispose (); 
pbImg .CreateGraphics ().DrawImage (img ,0,0); 
img .Dispose (); 

} 
} 

void PbImgMouseUp(object sender, MouseEventArgs e) 
{ 
flag =false ; 
temG =Graphics .FromImage (imgPic ); 
temG .DrawImage (imgTem,0,0); 
temG .Dispose (); 
} 

void PbImgPaint(object sender, PaintEventArgs e) 
{ 
Graphics g=e.Graphics ; 
g.DrawImage (imgPic ,0,0); 
} 
} 
} 
 
 用鼠标画直线产生重影

但是如果为imgPic和imgTem两个变量加入了背景色后就不会产生重影？
比如加入下面的代码：
Graphics g=Graphics .FromImage (imgPic );
g.FillRectangle (new SolidBrush (Color .Gray ),new Rectangle (0,0,pbImg .Width ,pbImg .Height ));
g.Dispose ();
g=Graphics .FromImage (imgTem );
g.FillRectangle (new SolidBrush (Color .Gray ),new Rectangle (0,0,pbImg .Width ,pbImg .Height ));
g .Dispose ();

------解决方案--------------------
简单的说


Graphics g=Graphics .FromImage (imgPic ); 
g.FillRectangle (new SolidBrush (Color .Gray ),new Rectangle (0,0,pbImg .Width ,pbImg .Height )); 
g.Dispose (); 
g=Graphics .FromImage (imgTem ); 
g.FillRectangle (new SolidBrush (Color .Gray ),new Rectangle (0,0,pbImg .Width ,pbImg .Height )); 
g .Dispose ();


在执行这个后其实还是重影~~ 只是不设置前面的是透明 你可以看到重影~~设置就看不到重影