ASP.NET Dynamic Gradient Handler

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Introduction

Gradients are an essential tool for any serious graphic designer. Disciplined use of gradients can provide a simple professional touch to virtually any graphical layout. However, HTML and CSS provide no intrinsic support for gradients. Generally, a tool such as Photoshop is used to save a static image file that is then tiled as a background. While this approach is effective, it can be tedious and inflexible because it requires an additional tool to manage the images.

The GradientHandler can eliminate needless steps when dealing with simple linear gradients. Gradients are defined with URL parameters, leading to a much more manageable code base.

Background

Only a basic ASP.NET understanding is needed to use the GradientHandler. However, knowledge of GDI+ and the ASP.NET IHttpHandler interface is needed to fully understand the inner workings.

Using the code

The GradientHandler can be easily configured for any .NET 2.0 or greater application. The files GradientHandler.cs and Utility.cs should be copied to the /App_Code directory under the root of the application. The Web.config file needs to include a declaration to map the GradientHandler class to a URL. Our examples map to Gradient.axd:

<system.web>
    <httpHandlers>
        <add path="Gradient.axd" verb="GET" 
          type="Elsinore.Website.GradientHandler"/>
    </httpHandlers>
</system.web>

The GradientHandler can be used most simply with a reference in the CSS:

body
{
    background: Black url(Gradient.axd?Orientation=Horizontal&
        Length=300&StartColor=000000&EndColor=FFFFFF) repeat-y;
}

This produces the following background on a simple page:

The GradientHandler can also be referenced programmatically, opening up more options. The following code allows the user to specify the gradient parameters:

Markup:

<body runat="server" id="body">
    <form id="form1" runat="server">
        Length:
        <asp:TextBox runat="server" ID="lengthBox" Text="300" />
        <br />
        StartColor:
        <asp:TextBox runat="server" ID="startColorBox" Text="#F00" />
        <br />
        FinishColor:
        <asp:TextBox runat="server" ID="finishColorBox" Text="#0F0" />
        <br />
        <asp:Button runat="server" Text="Submit" />
    </form>
</body>

Code:

protected void Page_Load(object sender, EventArgs e)
{
    // parse the parameters
    int length = int.Parse(this.lengthBox.Text);
    Color startColor = ColorTranslator.FromHtml(this.startColorBox.Text);
    Color finishColor = ColorTranslator.FromHtml(this.finishColorBox.Text);

    // generate css declaration
    string backgroundUrl = GradientHandler.GetUrl(Orientation.Vertical, 
                           length, startColor, finishColor);
    string backgroundCss = string.Format("{0} url({1}) repeat-x", 
                           this.finishColorBox.Text, backgroundUrl);
    this.body.Style.Add("background", backgroundCss);
}

In this example, the user can specify the length, the start color, and the finish color of the gradient. The static method GradientHandler.GetUrl is called with these parameters, and the declaration is added to the body tag. The result is as follows:

A live demo of this example is available at www.elsitech.com.

Points of interest

The GradientHandler specifically generates linear gradients, but other graphical shortcomings in HTML and CSS can also be solved with dynamic generation using ASP.NET HTTP handlers and GDI+. Rounded rectangles, advanced text effects, and image filters are just some of the opportunities.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

About the Author

Jake Morgan

Chief Technology Officer
Elsinore Technologies, The Issue Management Expert

United States

Member

Jake Morgan
Chief Technology Officer

CTO Jake Morgan brings a diverse background and over 7 years of software development experience to Elsinore, having created successful software applications in both the public and private sector, and founding a wildly popular online community.

Before joining Elsinore in 2005, Jake led the design and development of the NC FAST Online Verification system, used by the NC Department of Health and Human Services to verify eligibility for billions of dollars in benefits. He also spent time at Nortel Networks and founded the TheWolfWeb.com, a vibrant online community for NC State students, which supported over 15 million page views a month. At Elsinore he oversees the design and development of IssueNet Issue Management Software.

Jake is an alumnus of NC State University, where he received a BS in Mechanical Engineering.

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