Copying OpenGL context to a MemDC (Windows)

OpenGL OpenGL: Basic Coding
1

Hello,

I want to make a screenshot (within my program) from the context opengl is painting to.
Therefore I first used the DC of the window, but the problem is, that when another window is painted over my OpenGL window, then the screenshot contains the window above.

So I decided to copy the content of my OpenGL window into a MemoryDC.

What I did is something like

MemDC = CreateCompatibleDC(WindowDC);
…
OnDraw()
{
wglMakeCurrent(MemDC, m_OpenGL.m_HGLRC);
…
}

I hoped that now OpenGL paints into the MemDC but this seems to be wrong. Can someone help me what my mistake is (I am a beginner on DC and OpenGL… so type slowly :slight_smile:

BTW, I am using DoubleBuffer im my function and most of the time the function draws to a window.

Thanks a lot for your help,
Heiko

2

You need to go about recreating a GL context for the new DC.

Siwko

3

Why not just use glReadPixels? Use that to copy the color buffer into system memory and use its contents as the screenshot.

4

Originally posted by DFrey:
Why not just use glReadPixels?

According to my book this has the same problems that I am encountering in my current version. If something is above the OpenGL Window it may happen that this is exported too (depending on graphic hardware and drivers)

Heiko