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How To Get A Website Thumbnail in a C# Application Without Creating A Form (console)

, 5 Jul 2008
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The article describes how to get a thumbnail of a Website in .NET Framework 2.0+ without launching a fully interactive WinForms application.

UPDATE

I've updated the code and the binary with the great improvements that Piers Lawson suggested in the comments. The app should no longer have problems taking snapshots of some images with JavaScript or just plain random problems. It is also slightly optimized with suggestions from Frank Herget. It looks like he's based a very nice service around it on his site - check it out!

Thanks again for your great support!

Introduction

The article describes a console-like application that loads a Web page, makes a screenshot of it and saves it as a JPG file.

Our beloved sys admin - (we all bow to him and worship his skills) has recently asked if it's possible to write a .NET application to make a thumbnail of a Website. The task is pretty trivial with Windows Forms actually. But with him being the Linux guy and all... I decided to pick up the more challenging part of it being the console app. An interesting use case anyway.

In WinForms, all you really need to do is drop a WebBrowser from your Toolbox on your form and once it's loaded the page call:

Bitmap bitmap = new Bitmap(width, height);
webBrowser1.DrawToBitmap(bitmap, 
    new Rectangle(webBrowser1.Location.X, webBrowser1.Location.Y, 
        webBrowser1.Width, webBrowser1.Height));

Obvious enough. When it gets tricky is when you want to do it in a console application in a way that can take a shot of multitude of Websites provided in a batch file. There is a dirty way of instantiating a whole form, making it show (or not), doing the work and then exiting the WinForms app. This might probably be enough for a quick solution, but I wanted a clean piece of code, so I would actually NOT take pride in something in that tone.

How is it done then...

So we instantiate the Web control in our class constructor...

public WebPageBitmap(string url, int width, int height, bool scrollBarsEnabled)
{
    this.url = url;
    this.width = width;
    this.height = height;
    webBrowser = new WebBrowser();
    webBrowser.DocumentCompleted += new WebBrowserDocumentCompletedEventHandler(documentCompletedEventHandler);
    webBrowser.Size = new Size(width, height);
    webBrowser.ScrollBarsEnabled = scrollBarsEnabled;
}

Easy so far and pretty similar to what the regular app would do anyway. The documentCompletedEventHandler is a delegate to tell that it has loaded. (I initially wanted to use that for drawing the bitmap but deferred that to the point where the bitmap is actually fetched after I added the resizing part.) Now comes the interesting case.

The Neat Part

Since the call is asynchronous, a simple webBrowser.Navigate(URL); just won't cut it. We are in a single thread and the browser does not create a separate thread for that. This makes sense by the canonical windows rule: Only the thread that creates a control, accesses the control. We need to somehow allow the control to take the flow of the thread and do its work. Navigate only tells it that it should perform the action and immediately exits. The developer's responsibility then is to know when the control is ready for consumption. Which is the case when the webBrowser.ReadyState progresses to (or returns to) the state of WebBrowserReadyState.Complete.

The Solution

To pass the flow to the app controls, you need to perform Application.DoEvents(); which was a bit of a wild guess when I used it. Surprise, surprise, it works just like it did in other Windows frameworks that I used before.

public void Fetch()
{
    webBrowser.Navigate(url);
        while (webBrowser.ReadyState != WebBrowserReadyState.Complete)
        {
            Application.DoEvents();
        }
}

The effect is a tiny and neat (I hope) app that pulls a Web page from the net and makes a screenshot off of it (with possible rescaling).

You can get the source code or get the app directly. App usage:

GetSiteThumbnail.exe http://www.yoursite.com/ thumbnail.jpg 
  [browser_width(defaults to 800) browser_height (defaults to 600) ] 
  [thumbnail_width thumbnail_height]

Sample:
GetSiteThumbnail.exe http://www.cognifide.com/ cognifide.jpg 1280 1024 640 480

License

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

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About the Author

AdamNajmanowicz
Web Developer
Poland Poland
Adam Najmanowicz is a Senior Developer at Cognifide Poland.
 
His previous experience includes Delphi, .Net as well as Java Development.
 
Currently working on ASP.NET + MSSql Server(Oracle) solutions for enterprises.
 
Also developing desktop applications for Stardock Systems.

Comments and Discussions

 
QuestionSpurious behaviour Pinmembermillerbill2-Oct-12 1:35 
GeneralThank you Pinmemberquannt9124-Jul-12 18:22 
GeneralAgain ... NICE JOB! PinmemberBHUSCH16-Jul-09 9:10 
GeneralNice work PinmemberOwen Gunter5-Jul-09 11:42 
Generalnice app! PinmemberMember 223292820-Aug-08 10:40 
GeneralRe: nice app! PinmemberAdamNajmanowicz24-Aug-08 4:04 
GeneralRe: nice app! PinmemberMember 223292825-Aug-08 4:04 
Generalthankx PinmemberHari Om Prakash Sharma6-Jul-08 23:21 
GeneralA Better Way to capture website thumbnails PinmemberMember 456781829-May-08 14:58 
GeneralRe: A Better Way to capture website thumbnails PinmemberOwen Gunter5-Jul-09 11:46 
QuestionSystem.UnauthorizedAccessException [modified] Pinmemberapokalypse_14-Sep-07 12:08 
GeneralDoesn't work for me Pinmemberras7819-Jul-07 23:32 
GeneralWindows namespace or type not found Pinmemberpinkarton7-May-07 15:07 
QuestionCan Java do it? Pinmemberpinkarton23-Apr-07 15:18 
AnswerRe: Can Java do it? PinmemberAdamNajmanowicz24-Apr-07 7:37 
GeneralThumbnail width and height parameters Pinmembertbenami28-Mar-07 20:25 
GeneralRe: Thumbnail width and height parameters Pinmembergafrancisco20-Jul-10 13:38 
QuestionBlank Image on Websites with Java Applets PinmemberJon Ebersole9-Feb-07 12:29 
Questionwhy I just get blank image? Pinmemberkai.ma24-Dec-06 21:15 
AnswerRe: why I just get blank image? Pinmembermethai189-Apr-07 13:31 
GeneralRe: why I just get blank image? PinmemberZhongjie Li9-May-07 9:09 
GeneralRe: why I just get blank image? PinmemberZhongjie Li10-May-07 3:47 
GeneralRe: why I just get blank image? PinmemberPiers Lawson25-May-07 2:37 
According to MSDN, the DrawToBitmap method is not supported for the WebBrowser control, which is why some pages render OK and others don't. If you look into this problem, some people have problems with pages showing Java. For me simple pages like www.google.co.uk would not render.
 
The only sure fire way round I found was to fall back to using the raw interfaces:
 
1) Add a reference to MSHTML.tlb
 
2) Create your own version of IHTMLElementRender which uses an IntPtr rather than _RemotableHandle:
 

[InterfaceType(1)]
[Guid("3050F669-98B5-11CF-BB82-00AA00BDCE0B")]
public interface IHTMLElementRender2
{
void DrawToDC(IntPtr hdc);
void SetDocumentPrinter(string bstrPrinterName, ref _RemotableHandle hdc);
}

 
2) Use this code to capture the initial web page image:
 

IHTMLDocument2 rawDoc = (IHTMLDocument2)hiddenWebBrowser.Document.DomDocument;
IHTMLElement rawBody = rawDoc.body;
IHTMLElementRender2 render = (IHTMLElementRender2)rawBody;
 
Bitmap screenCapture = new Bitmap(width, height);
Rectangle drawRectangle = new Rectangle(0, 0, width, height);
myWebBrowser.DrawToBitmap(screenCapture, drawRectangle);
Graphics graphics = Graphics.FromImage(screenCapture);
 
IntPtr graphicshdc = graphics.GetHdc();
render.DrawToDC(graphicshdc);
bmpg.ReleaseHdc();
bmpg.Dispose();

GeneralRe: why I just get blank image? Pinmembertreeleung22-Apr-08 12:27 
GeneralRe: why I just get blank image? PinmemberilKaleez15-May-08 3:12 
GeneralRe: why I just get blank image? PinmemberAdamNajmanowicz5-Jul-08 2:09 
AnswerRe: why I just get blank image? [modified] PinmemberoCasper14-Oct-07 11:42 
GeneralWhy It Does not work with some sites Pinmembermhariri27-Nov-06 5:39 
GeneralAxWebBrowser Vs. WebBrowser (.NET2) events PinmemberAssaf Koren23-Nov-06 8:43 
GeneralRe: AxWebBrowser Vs. WebBrowser (.NET2) events PinmemberAdamNajmanowicz28-Nov-06 8:23 
GeneralGetting it to work in an ASP.NET application [modified] PinmemberdB.20-Nov-06 20:51 
GeneralRe: Getting it to work in an ASP.NET application Pinmemberligaz25-Nov-06 4:06 
GeneralRe: Getting it to work in an ASP.NET application PinmemberdB.25-Nov-06 5:11 
GeneralRe: Getting it to work in an ASP.NET application PinmemberAdamNajmanowicz28-Nov-06 8:19 
GeneralRe: Getting it to work in an ASP.NET application Pinmemberchr872-Mar-07 2:19 
GeneralRe: Getting it to work in an ASP.NET application PinmemberChris Vann23-Mar-08 10:46 

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