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to take a screenshot of a web page using an hidden window?

Posted on 2009-04-03
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Last Modified: 2013-12-17
In a C++ desktop application, is it possible to load a web page with the IE rendering engine in a hidden window and take a screenshot of that hidden page? if so, how?
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Question by:lucavilla
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Expert Comment

by:Craig Wagner
ID: 24060918
I needed to do something very similar (was using an embedded Mozilla browser in my app). I never found a way to accomplish what you're asking, I had to render the page to the screen and then take a screenshot of the area.

In case you end up having to go that route, I attached the code I used. In the attached code, "this" refers to the web browser control itself (we created a custom control to encapsulate this, and other, functionality).
/// <summary>
/// Returns an image of the rendered item as a Bitmap object.
/// </summary>
/// <remarks>
/// It is up to the caller of this method to dispose of the Bitmap
/// object returned when the caller is finished with it.
/// </remarks>
/// <returns>
/// A Bitmap object containing the rendering of the current item.
/// </returns>
public Bitmap GetItemAsBitmap()
{
    // NOTE: You cannot wrap the Bitmap declaration in a using 
    //       statement as that causes the Bitmap object to be 
    //       disposed before the caller receives it. It is up to
    //       the caller to dispose of the Bitmap.
 
    // Get a reference to the drawing surface of the control
    using( Graphics source = this.CreateGraphics() )
    {
        // Create a bitmap that is the same width, height, and
        // resolution as the control
        Bitmap bitmap = new Bitmap( this.Width, this.Height, source );
 
        // Create a graphics object on the blank bitmap so we can
        // draw into it
        using( Graphics target = Graphics.FromImage( bitmap ) )
        {
            // Get the screen coordinates of this control; we are looking
            // for a point relative to the top left of the control (this)
            // offset by x = 0 and y = 0 (Point.Empty)
            Point screen = this.PointToScreen( Point.Empty );
 
            // Copy from the screen into the bitmap (via the Graphics
            // object)
            target.CopyFromScreen( screen.X, screen.Y, 0, 0, this.Size );
 
            return bitmap;
        }
    }
}

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Author Comment

by:lucavilla
ID: 24062627
Thanks CraigWagner for your very kind answer with code.

I keep this question open for a solution with the window hidden, if such a solution exists.
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Accepted Solution

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DanRollins earned 500 total points
ID: 24163749
I, too have explored the issue of making a program render to an off-screen bitmap, and had at best mixed results.  One try is to send the window a WM_PRINTCLIENT message:
    WM_PRINTCLIENT Message
    http://msdn.microsoft.com/en-us/library/dd145217(VS.85).aspx
But  not all windows handle that message, and anyway, if it is not your own application (e.g., an external webbrowser) then there are serious problems in setting up the DC in that app's address space, etc.
See these EE links:
http://www.experts-exchange.com/Programming/System/Windows__Programming/MFC/Q_20780945.html
http://www.experts-exchange.com/Programming/Languages/CPP/Q_20309208.html
Your best bet would be to display the window visibly (breifly) and take the snapshot, then hide it again.
Assuming the window must remain hidden, your next best bet would be to try embedding a webbrowser control into your own app and sending the WM_PRINTCLIENT message to it.  But I'm not at all certain how successful that will be.
Outside of the box:
You might add a secondary video adapter (withh no video monitor) and have the window display on that one -- it would be hidden from the user's view but still provide a bitmap surface for rendering
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Author Closing Comment

by:lucavilla
ID: 31566266
Better than nothing.  Thanks!
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