Graphics on the Fly Directly from ASP.NET Server Control without .ASPX page

Introduction

This is a simple article to demonstrate rendering a graphic image on the fly from within a server control without using an .aspx page. One caveat, I have not gotten this method to work at design time, only run time.

On an .aspx page, you would normally create a bitmap with GDI+, and then use this syntax to draw it:

Response.ContentType = "image/jpeg";
objBitmap.Save(Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg); 

The only examples I had seen which created graphics on the fly (buttons and charts) all included an .aspx page which they would call from the Render method with a query string. The .aspx page would then render the graphic based on the query string.

Here is a way to render the graphic at runtime without the .aspx page.

using System.Drawing;
using System.Drawing.Imaging;
//... 
protected override void Render(HtmlTextWriter output) 
{ 
  Bitmap objBitmap = new Bitmap(120,30); 
  Graphics objGraphics = Graphics.FromImage(objBitmap);
  //Fill the background 
  objGraphics.FillRectangle(new SolidBrush(Color.LightBlue),0,0,120,30); 
  //Create blue-yellow bullet point 
  objGraphics.FillEllipse(new SolidBrush(Color.Blue),3,9,10,10); 
  objGraphics.FillEllipse(new SolidBrush(Color.Yellow),4,10,8,8); 
  //Draw text next to bullet point 
  objGraphics.DrawString("Submit", new Font("Tahoma",8), 
                     new SolidBrush(Color.Green), 16,8); 
  //Render 
  Page.Response.Clear(); 
  Page.Response.ContentType = "image/jpeg"; 
  objBitmap.Save(Page.Response.OutputStream, 
      System.Drawing.Imaging.ImageFormat.Jpeg); 
  //Tidy up 
  objGraphics.Dispose(); 
  objBitmap.Dispose(); 
}

I am not sure of the implications of writing directly to the Page class from within the Render method, but this works at runtime. If anyone knows of a method that works at design time, please let me know.

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