如何在ASP.NET页面中自动生成并显示透明的GIF图片

在页面中加入一个图片控件，并将它的Style属性设为：FILTER: chroma(color:#000000) ，原因是自动生成的GIF图片总是黑色背景。然后在后台代码中写入如下代码。(见DEMO)

using System;

using System.Collections;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Web;

using System.Web.SessionState;

using System.Web.UI;

using System.Web.UI.WebControls;

using System.Web.UI.HtmlControls;

using System.IO;

using System.Drawing.Drawing2D;

namespace WebPageIndex

{

/// <summary>

/// WebForm1 的摘要说明。

/// </summary>

public class WebForm1 : System.Web.UI.Page

{

protected System.Web.UI.HtmlControls.HtmlImage IMG1;

private void Page_Load(object sender, System.EventArgs e)

{

// 在此处放置用户代码以初始化页面

MyTempImage myTempImage=new MyTempImage();

IMG1.Src=myTempImage.CreateImage();

}

public class MyTempImage : Page

{

public string CreateImage()

{

string str="兴中公司财务章";

Bitmap image=new Bitmap(300,300);

Graphics g=Graphics.FromImage(image);

string thefullname=Server.MapPath("/")+"\\nowtime.gif";

Pen p=new Pen(Brushes.Red,10);

Pen p1=new Pen(Brushes.Red,5);

SolidBrush b=new SolidBrush(Color.Red);

g.SmoothingMode=SmoothingMode.AntiAlias;

Point point1 = new Point( 150, 50);

Point point2 = new Point(50, 150);

Point point3 = new Point(230, 150);

Point[] curvePoints =

{

point1,

point2,

point3,

};

g.FillPolygon(b,curvePoints,FillMode.Winding );

g.DrawEllipse(p,10,10,280,280);

g.DrawString(str,new Font("隶书",20,FontStyle.Bold),new

SolidBrush(Color.FromArgb(255, 255,0, 0)),40,200);

g.DrawLine(p1,80,240,220,240);

g.DrawLine(p1,80,250,220,250);

image.Save(thefullname,System.Drawing.Imaging.ImageFormat.Gif);

return "/nowtime.gif";

}

#region Web 窗体设计器生成的代码

override protected void OnInit(EventArgs e)

{

// CODEGEN: 该调用是 ASP.NET Web 窗体设计器所必需的。

InitializeComponent();

base.OnInit(e);

}

/// <summary>

/// 设计器支持所需的方法 - 不要使用代码编辑器修改

/// 此方法的内容。

/// </summary>

private void InitializeComponent()

{

this.Load += new System.EventHandler(this.Page_Load);

}

#endregion

}

运行结果图：