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copied!<p>This problem is actually common (apparently) in game code and the like. One interesting solution is the following: <a href="https://stackoverflow.com/questions/2944290/efficient-pixel-shader-sum-of-all-pixels">Efficient pixel shader sum of all pixels</a>. This is particularly relevant to your exact situation, since you can use a larger mimmap texture to sum smaller segments of the display. </p> <p><a href="https://stackoverflow.com/questions/10819951/how-to-copy-frontbuffer-data-to-texture-directx-9">Get the screen into a texture</a></p> <pre><code>IDirect3DTexture9* texture; // needs to be created, of course IDirect3DSurface9* dest = NULL; // to be our level0 surface of the texture texture->GetSurfaceLevel(0, &dest); pD3DDevice->StretchRect(pSurface, NULL, dest, NULL, D3DTEXF_LINEAR); </code></pre> <p>And then create a mipmap chain as <a href="http://msdn.microsoft.com/en-us/library/windows/desktop/bb206251%28v=vs.85%29.aspx" rel="nofollow noreferrer">here</a></p> <pre><code>// This code example assumes that m_d3dDevice is a // valid pointer to a IDirect3DDevice9 interface IDirect3DTexture9 * pMipMap; m_pD3DDevice->CreateTexture(256, 256, 5, 0, D3DFMT_R8G8B8, D3DPOOL_MANAGED, &pMipMap); </code></pre> <p>Of course you don't have to access the bottom mipmap (which is the average). You could access a few levels higher to get averages of sections. Also this is quick because texture mipmapping is important in games and graphics in general. Other filtering options may be available too.</p> <p>For the second edit try <a href="https://stackoverflow.com/questions/120066/doing-readback-from-direct3d-textures-and-surfaces">here</a> - something about textures in gpu mem are read differently, and can't be locked, you'll need to use getrendertargetdata or some such. <a href="http://msdn.microsoft.com/en-us/library/bb174405%28VS.85%29.aspx" rel="nofollow noreferrer">This</a> can be used to copy your stretchrect surface to a texture created cpu side in the system pool. As far as I know gpu side textures/surfaces can't be memcpy'ed directly.</p>

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