Capturing screen shot from webBrowser control in C#

Question

I'm using the webBrowser control and trying to capture a screen shot from it. I start up the webBrowser control and set its URL to some web page. It displays just fine. Then, in response to a button press, I capture the image of the page that's contained within the webBrowser control, like this:

Bitmap bitmap = new Bitmap(webBrowser.Width, webBrowser.Height);
webBrowser.DrawToBitmap(bitmap, new Rectangle(0, 0, webBrowser.Width, webBrowser.Height));

And it does indeed get the page image and I can display it in a pictureBox control.

But a problem occurs when I click on a link in the displayed page and it goes to some other page. If I then click my "grab the page image" button, which again invokes the above code, the image that I get is completely white, even though the page is displayed properly within the webBrowser control.

If I stay on the initial web page I can repeatedly grab the image and display it. But whenever I go to some other subsequent page (which loads into the same webBrowser control) the image that gets grabbed is just plane white.

What do I have to do to get it to get the image from subsequently loaded pages?

Steve Dawkins · Answer

I've also been using the DrawToBitMap method in an HTTP Handler *.ashx running under SharePoint. What I've discovered is that it will capture bitmaps only once per instance of the WebBrowser object and only if the user account associated with the IIS Application pool is logged on. It works even if the user account is logged on to a disconnected RDP session. Can any explain why the logged on user makes such a difference?

Vulpes · Answer

Yes WebBrowser derives from WebBrowserBase and so inherits its DrawToBitmap() method. As Sam said there's quite a lot of this sort of thing in the .NET Framework though sometimes you actually get a 'not supported exception' if you try to call such a method or property. As it also says in the docs that it's 'infrastructure' I suspect they haven't done that here so that it can if necessary be called by MS's own developers who will know its limitations.

Sam Hobbs · Answer

There is a lot of that in .Net. That is methods and properties that exist but are not useful. Note that it is at least somewhat understandable since all classes except the object class derives from classes. Perhaps the bad design is the practice of using methods and properties in classes and interfaces that are not used in many classes that derive from it. Something else that has caused me confusion is that sometimes WPF and Windows Forms have the same names for classes that are very different.

Roger Garrett · Answer

Well that's interesting. Thank you for that info. Strange how Microsoft let's you invoke it provides it as a method of the webBrowser control shows it as one of the available methods when using Visual Studio C# but then in the documentation says that This method is not supported by this control. Very strange.

Roger Garrett · Answer

No that's not it. I'm using my own website for these tests and I definitely don't do anything on my website to disable anything like that.

Sam Hobbs · Answer

Are you sure that the web site is not intentionally disabling the feature? There are many web sites (such as IMDB.com) that don't want us to copy images.

Vulpes · Answer

According to the MSDN documentation ( http://msdn.microsoft.com/en-us/library/system.windows.forms.webbrowserbase.drawtobitmap.aspx ) the WebBrowser.DrawToBitmap method isn't actually supported so I'm surprised it works at all! Could you use the Graphics.CopyFromScreen method ( http://msdn.microsoft.com/en-us/library/6yfzc507.aspx ) instead ?