Remeber state of pixel in HLSL DirectX10
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i have a little problem and i wanna know it's a good way to resolve it.
I change many pixel color on my application (cellular automata) on GPU.
I swap render targets to get actual back-buffer and later i put it to my Pixel-shader, in next frame operation is repeat.
My problem i when wanna know the pixel is changed in last frame.

I know i can solve it by use one more render target (3 RT) and remember my specific data per pixel, but i think it can be made some performance issue. Maybe is some other way to do it. I use DirectX10.

 Really thanks for help.