Web Graphics On The Fly in ASP.NET

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Introduction

We all know what it is like when it comes to creating graphics for the web. Mind you, I find this to be a very tedious job, in fact many times I will try to avoid it. There have been other ways to create graphics on the fly, in fact you may wish to read an article written on VML posted here at The Code Project.

While there is nothing wrong using this or any other method available we all know the future ( at least in Microsoft’s eyes) is .NET. With that said, I would like to show you a method for creating dynamic graphics for the web in ASP.NET. Keep in mind that all of the following code will be done in VB.NET & C# as well.

To Begin

The use of namespaces is vital in the .NET environment. We must import the proper namespaces to allow us to access the methods and properties we call in the following code below. I have updated this article to include the C# version of the code, you will notice how very similar they are.

‘=====================================
‘Include All Pertinent Namespaces Here
‘=====================================

<%@ Page Language="VB" ContentType="image/jpeg" %>
<%@ Import Namespace="System.Drawing" %>
<%@ Import Namespace="System.Drawing.Text" %>
<%@ Import Namespace="System.Drawing.Imaging" %>
<%@ Import Namespace="System.Drawing.Drawing2D" %>

	<%

	Response.Clear( )
	Dim height As Integer = 100
	Dim width As Integer = 200
	Dim r As New Random
	Dim x  As Integer = r.Next(75)

	Dim bmp As new Bitmap(width, height, PixelFormat.Format24bppRgb)
	Dim g as Graphics = Graphics.FromImage(bmp)
	
	g.TextRenderingHint = TextRenderingHint.AntiAlias
	g.Clear(Color.Orange)
	g.DrawRectangle(Pens.White, 1, 1, width-3, height-3)
	g.DrawRectangle(Pens.Gray, 2, 2, width-3, height-3)
	g.DrawRectangle(Pens.Black, 0, 0, width, height)
	g.DrawString("The Code Project", _
			New Font("Arial", 12, FontStyle.italic), _
			SystemBrushes.WindowText, New PointF(x,50))


	bmp.Save(Response.OutputStream, ImageFormat.Jpeg)
	g.Dispose( )
	bmp.Dispose( )
	Response.End( )
	
	%>

C# Version

<%@ Page Language="C#" ContentType="image/jpeg" %>
<%@ Import Namespace="System.Drawing" %>
<%@ Import Namespace="System.Drawing.Text" %>
<%@ Import Namespace="System.Drawing.Imaging" %>
<%@ Import Namespace="System.Drawing.Drawing2D" %>

	<%

	Response.Clear();
	int height = 100;
	int width = 200;
	Random r = new Random();
	int x = r.Next(75);

	Bitmap bmp = new Bitmap(width, height, PixelFormat.Format24bppRgb);
	Graphics g = Graphics.FromImage(bmp);
	
	g.TextRenderingHint = TextRenderingHint.AntiAlias;
	g.Clear(Color.Orange);
	g.DrawRectangle(Pens.White, 1, 1, width-3, height-3);
	g.DrawRectangle(Pens.Gray, 2, 2, width-3, height-3);
	g.DrawRectangle(Pens.Black, 0, 0, width, height);
	g.DrawString("The Code Project", new Font("Arial", 12, FontStyle.Italic), 
	SystemBrushes.WindowText, new PointF(x,50) );

	bmp.Save(Response.OutputStream, ImageFormat.Jpeg);
	g.Dispose();
	bmp.Dispose();
	Response.End();
	
	%>

Code Explanation

While there is not a lot to this code I would like to explain what is going on here. To begin we clear the Response object. The variables height and width are defined as the dimensions of our image, you can adjust as you wish or create a subroutine where you pass these values in. So far this is rather rudimentary, nothing extremely extensive so far. Next we will declare a variable r to be of type Random. The integer variable x on the next line is assigned a random value using r with a seed value of 75, you can use whatever seed value you would like.

The next two objects that we create will be new for any ASP web developers. First we are to create a new Bitmap object, this item will define the area to which we are doing our drawing on. There are three arguments that are passed to it, the width and height of our image and the pixel format. There are a series of different pixel formats to choose from, here is a detailed explanation of the different types available to you.

Next we will use the graphics object to set the TextRenderingHint to TextRenderingHint.AntiAlias. This allow us to take advantage of antialiasing characteristics when displaying fonts. Antialiasing allows you to get ride of jagged lines in your text by blending shades of gray or color around the text to make it appear smoother.

On the next line we are actually setting the main color of our bitmap image. I choose Code Project orange for this example :). In the next three lines we are actually going to begin drawing on our image. The method that gets called is the same, only changing a few of the parameters. We are actually just drawing a framework at the edge of the image. Essentially you can see that by the points being specified in the arguments list. Here is a breakdown of how the DrawRectangle works; keep in mind the x and y coordinates are in terms of the upper left hand corner:

g.DrawRectangle( [Pen],[x],[y],[width],[height] )	

Next we will actually draw some text onto our Bitmap object. The DrawString method is overloaded and takes a series of arguments that are specified like this for my example:

g.DrawString( [String],[Font], ,[PointF] )

For the first time we will go ahead and make a direct method call using the Bitmap object. The method to save our bitmap is simply Save which is overloaded (big surprise) passing the outputstream object and image format. Here is another list of options you have in regards to your image format.

There have been questions regarding the next two lines of code, I am calling the Dispose method for both the Graphics object and Bitmap object that we created. Even though .NET development can manage our object(s) with respect to garbage collection, it is always a good idea to clear these items when you know you are done with them. You can exclude these two calls and garbage collection will still take place, it's your call.

Conclusion

That’s all it takes to create dynamic graphics through the use of code alone.

Other Articles

Article on MSDN entitled: Create Snazzy Web Charts and Graphics On the Fly with the .NET Framework.

Update History

• February 13th, 2002 - Original article is posted.
• July 18th, 2002 - Updated to include code explanation section.
• November 25th, 2002 - Updated to include C# code example.
• November 26th, 2002 - Updated to allow AntiAlias to work properly thanks to leppie.