Improvement to HIP CAPTCHA control for Blog Engines

This is a small improvement to HIP CAPTCHA control (CAPTCHA for blog engines based ASP.NET). (Hey Miguel). It also demonstrates how to use HtmlTextWriter to render HTML properly in ASP.NET. Forget about writing HTML strings. You have to write a bit more code, but you get well-formatted HTML with automatic support for older browsers.

protected override void Render(HtmlTextWriter writer)
{
    StringBuilder sb = new StringBuilder();
    sb.Append("?iw="); 
    sb.Append(this._imageWidth);
    sb.Append("&ih="); 
    sb.Append(this._imageHeight);
    sb.Append("&tc="); 
    sb.Append(this._textColor.ToArgb());
    sb.Append("&tpc="); 
    sb.Append(this._textPatternColor.ToArgb());
    sb.Append("&bc="); 
    sb.Append(this._backgroundColor.ToArgb());
    sb.Append("&bpc="); 
    sb.Append(this._backgroundPatternColor.ToArgb());
    sb.Append("&tp="); 
    sb.Append(this._textPattern.ToString());
    sb.Append("&bp="); 
    sb.Append(this._backgroundPattern.ToString());
    sb.Append("&fs="); 
    sb.Append(this._fontSize);
    sb.Append("&hc="); 
    sb.Append(HttpUtility.UrlEncode(this._hipCode));

    string strControlMessage = this._controlMessage;
    if (strControlMessage.Length <= 0)
    {
        strControlMessage = "Enter the code you see";
    }

    //
    // render writer
    writer.AddAttribute(HtmlTextWriterAttribute.Cellpadding, "0");
    writer.AddAttribute(HtmlTextWriterAttribute.Cellspacing, "0");
    writer.AddAttribute(HtmlTextWriterAttribute.Border, "0");
    writer.RenderBeginTag(HtmlTextWriterTag.Table);
    writer.RenderBeginTag(HtmlTextWriterTag.Tr);
    writer.AddAttribute(HtmlTextWriterAttribute.Rowspan, "2");
    writer.RenderBeginTag(HtmlTextWriterTag.Td);
         
    // image
    writer.AddAttribute(HtmlTextWriterAttribute.Src,
        "HIPGenerator.aspx" + sb.ToString());
    writer.AddAttribute(HtmlTextWriterAttribute.Width,
        this._imageWidth.ToString()); 
    writer.AddAttribute(HtmlTextWriterAttribute.Height,
        this._imageHeight.ToString());
    writer.AddStyleAttribute("border",
        String.Format("{0} solid {1}px",
        this._imageBorderColor.ToKnownColor(),
        this._imageBorderSize));
    writer.RenderBeginTag(HtmlTextWriterTag.Img);
    writer.RenderEndTag();

    writer.RenderEndTag();
    writer.RenderBeginTag(HtmlTextWriterTag.Td);

    // span
    writer.AddStyleAttribute("font-family", "verdana");
    writer.AddStyleAttribute("font-size", "6pt");
    writer.RenderBeginTag(HtmlTextWriterTag.Span);
    writer.Write(strControlMessage + ":");
    writer.RenderEndTag();

    writer.RenderEndTag();
    writer.RenderEndTag();
    writer.RenderBeginTag(HtmlTextWriterTag.Tr);
    writer.AddAttribute(HtmlTextWriterAttribute.Align, "left");
    writer.RenderBeginTag(HtmlTextWriterTag.Td);
         
    // input text
    writer.AddAttribute(HtmlTextWriterAttribute.Type, "text");
    writer.AddAttribute(HtmlTextWriterAttribute.Id, this.UniqueID);
    writer.AddAttribute(HtmlTextWriterAttribute.Name, this.UniqueID);
    writer.AddAttribute(HtmlTextWriterAttribute.Maxlength,
        this.CodeLenght.ToString());
    writer.RenderBeginTag(HtmlTextWriterTag.Input);
    writer.RenderEndTag();

    writer.RenderEndTag();
    writer.RenderEndTag();

    if (this._validationMode == PersistMode.Forms)
    {
        writer.RenderBeginTag(HtmlTextWriterTag.Tr);
        writer.AddAttribute(HtmlTextWriterAttribute.Colspan, "2");
        writer.RenderBeginTag(HtmlTextWriterTag.Td);

        // input hidden
        writer.AddAttribute(HtmlTextWriterAttribute.Type, "hidden");
        writer.AddAttribute(HtmlTextWriterAttribute.Id, "hipCodeEnc");
        writer.AddAttribute(HtmlTextWriterAttribute.Name, "hipCodeEnc");
        writer.AddAttribute(HtmlTextWriterAttribute.Value, this._hipCode);
        writer.RenderBeginTag(HtmlTextWriterTag.Input);
        writer.RenderEndTag();

        writer.RenderEndTag();
        writer.RenderEndTag();
    }

    writer.RenderEndTag();
}

Related Posts:

• Fighting Comment Spam with CAPTCHA

test

test2

You should enter only letters and numbers all the other signs might be too confuseing to the user.
I saw in code project an example with real images but this one seems better.
Thanks

Yoav: thanks.
Site is oriented to the professional users mostly, so I don't see the problem. Other signs right now are: "@,!,". Anyway there would come improvements and I'll take your advice into the account.

Btw, if anybody sees the ways to improve the captcha, please feel free to live comment (and your credit card number...) here.

nice to hear u again.

nice to hear you too, what's your name, by the way ?

Good ! thank the author.

thnx

I saw in code project an example with real images but this one seems better .