Why do DirectX fullscreen applications give black screenshots?

Question

You may know that trying to capture DirectX fullscreen applications the GDI way (using BitBlt()) gives a black screenshot.

My question is r

Answer 1

I believe it is actually due to double buffering. I'm not 100% sure but that was actually the case when I tested screenshots in OpenGL. I would notice that the DC on my window was not the same. It was using two different DC's for this one game.. For other games I wasn't sure what it was doing. The DC was the same but swapbuffers was called so many times that I don't think GDI was even fast enough to screenshot it.. Sometimes I would get half a screenshot and half black..

However, when I hooked into the client, I was able to just ask for the pixels like normal. No GDI or anything. I think there is a reason why we don't use GDI when drawing in games that use DirectX or OpenGL..

You can always look at ways to capture the screen here:http://www.codeproject.com/Articles/5051/Various-methods-for-capturing-the-screen

Anyway, I use the following for grabbing data from DirectX:

HRESULT DXI_Capture(IDirect3DDevice9* Device, const char* FilePath)
{
    IDirect3DSurface9* RenderTarget = nullptr;
    HRESULT result = Device->GetBackBuffer(0, 0, D3DBACKBUFFER_TYPE_MONO, &RenderTarget);
    result = D3DXSaveSurfaceToFile(FilePath, D3DXIFF_PNG, RenderTarget, nullptr, nullptr);
    SafeRelease(RenderTarget);
    return result;
}

Then in my hooked Endscene I call it like so:

HRESULT Direct3DDevice9Proxy::EndScene()
{
    DXI_Capture(ptr_Direct3DDevice9, "C:/Ssers/School/Desktop/Screenshot.png");

    return ptr_Direct3DDevice9->EndScene();
}

You can either use microsoft detours for hooking EndScene of some external application or you can use a wrapper .dll.