wglMakeCurrent fails + WGL_NV_gpu_affinity

[dimensionX]

System config:-
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Windows XP 32-bit
Single Quadro FX 4600
Driver version 197.54

I'm trying to understand the WGL_NV_gpu_affinity extension. I know that I have only 1 GPU at the moment and I actually dont need to use this extension. My application will have to scale to multiple GPUs eventually.

1) hWnd = CreateWindow()
2) hDC = GetDC(hWnd)
3) hRC = wglCreateContext(hDC)

4) affDC = wglCreateAffinityDCNV(hGPU)
5) affRC = wglCreateContext(affDC)

Things that work:-
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Case 1:
wglMakeCurrent(hDC, hRC);
- The usual and it works fine.

Case 2:
wglMakeCurrent(affDC, affRC);
- This works fine too.

Case 3:
wglMakeCurrent(hDC, affRC); => regularDC + affinityRC
- It does not work. wglMakeCurrent() call FAILS.

According to the spec of WGL_NV_gpu_affinity it is legal to do this. Did anyone have this problem ?

[MalcolmB]

Is the pixel formats of the hDC and affDC the same? They need to be.
Are you remembering to set the pixel format of the affDC?

[dimensionX]

yes, I have set the pixel format for affDC and they have the same pixel format.

[MalcolmB]

Does GetLastError() return anything useful?

[dimensionX]

Apologies, my pixel format was different. After making it the same it works fine but have different problem now.

Problem:-
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1) Create win1 on disp1 connected to gpu1
2) Create win2 on disp2 connected to gpu2
3) Create (hDC1, hRC1) & (affDC1, affRC1) for win1/gpu1
4) Create (hDC2, hRC2) & (affDC2, affRC2) for win2/gpu2

Drawing white to win1 & win2
5) wglMakeCurrent(hDC1, affRC1) and glClear(GL_COLOR_BUFFER_BIT)
6) wglMakeCurrent(hDC2, affRC2) and glClear(GL_COLOR_BUFFER_BIT)

- Step 5 displays white on win1
- Step 6 DOES NOT display white on win2 ?
- When win1 spans across disp1 & disp2, with step 5, I thought it should clear only the portion of win1 that belongs to disp1/gpu1 but clears the entire win1 (even the portion that is on disp2/gpu2)

The wglMakeCurrent calls are successful and no GL errors either.

[MalcolmB]

I've learn that on certain setups, on new Nvidia drivers, the behavior for GPU affinity has changed (sadly). This is how things work on Windows 7 also, but they've brought it back to XP also.
You can't bind a affinity RC to a window DC (except for the first GPU it seems). You should do your rendering to an FBO using the affinity DC + affinity RC.
Then copy the frame to a texture in a non-affinity RC (bound to the windows DC) using
WGL_NV_COPY_IMAGE
http://www.opengl.org/registry/specs/NV/copy_image.txt

Render the texture as a screen aligned quad.