Screen capture of MDI app with OpenGL graphics using MFC

Question

In our MDI application - which is written in MFC - we have a function to save a screenshot of the MDI client area to file. We are currently doing a BitBlt from the screen into a bitmap, which is then saved. The problem is that some of the MDI child windows have their content rendered by OpenGL, and in the destination bitmap these areas show up as blank or garbled.

I have considered some alternatives:
- Extract the OpenGL content directly (using glReadPixels), and draw this to the relevant portions of the screen bitmap.
- Simulate an ALT+PrtScr, since doing this manually seems to get the content just fine. This will trash the clipboard content, though.
- Try working with the DWM. Appart from Vista and Win7, this also needs to work on Win2000 and XP, so this probably isn't the way to go.

Any input will be appreciated!

Answer 1

The best way to get a bitmap from an OpenGL window is to draw the content to a bitmap 'window'. See PFD_DRAW_TO_BITMAP for more information on how to do this.

If you want to go with the Alt+PrtScr way, you have to consider that many users have their own print screen tool installed which reacts on that very same hotkey. So you can't be sure that this hotkey will copy the content to the clipboard. It may just open the window of the installed print screen tool/utility.

Answer 2

Use the glReadPixels() approach. This question is asked quite often, here, on the gamedev.net forums and on other places, so google should show you code samples easily, but the glReadPixels() approach is the generally recommended approach.

Simulating keypresses is a recipe for disaster, I would stay away from that.