Can I use a shader to find the “difference” between two textures? (XNA / HLSL)

Question

I created a simple webcam that detects “motion edges”, so I draw a texture that shows where the pixels of the current frame are significantly different from the previous frame. This is my code:

// LastTexture is a Texture2D of the previous frame.
// CurrentTexture is a Texture2D of the current frame.
// DifferenceTexture is another Texture2D.
// Variance is an int, default 100;

Color[] differenceData = new Color[CurrentTexture.Width * CurrentTexture.Height];
Color[] currentData = new Color[CurrentTexture.Width * CurrentTexture.Height];
Color[] lastData = new Color[LastTexture.Width * LastTexture.Height];

CurrentTexture.GetData<Color>(currentData);
LastTexture.GetData<Color>(lastData);

for (int i = 0; i < currentData.Length; i++)
{
    int sumCD = ColorSum(currentData[i]); // ColorSum is the same as c.R + c.B + c.G where c is a Color.
    int sumLD = ColorSum(lastData[i]);
    if ((sumCD > sumLD - Variance) && (sumCD < sumLD + Variance))
        differenceData[i] = new Color(0, 0, 0, 0); // If the current pixel is within the range of +/- the Variance (default: 100) variable, it has not significantly changes so is drawn black.
    else
        differenceData[i] = new Color(0, (byte)Math.Abs(sumCD - sumLD), 0); // This has changed significantly so is drawn a shade of green.
}

DifferenceTexture = new Texture2D(game1.GraphicsDevice, CurrentTexture.Width, CurrentTexture.Height);
DifferenceTexture.SetData<Color>(differenceData);

LastTexture = new Texture2D(game1.GraphicsDevice,CurrentTexture.Width, CurrentTexture.Height);
LastTexture.SetData<Color>(currentData);

Is there a way to offload this calculation to a GPU using shaders (it can go at about 25/26 frames per second using the above method, but it's a bit slower)? I have a basic understanding of how HLSL shaders work and do not wait for a complete solution, I just want to know if it will be possible and how to get the "difference" texture data from the shader, and if it will actually be faster.

Thanks in advance.

Answer 1

, .Net Parallel Extensions CTP Microsoft. microsoft.com

XBox360, XNA, .

, :

for (int i = 0; i < currentData.Length; i++)
{
    // ...
}

:

Parallel.For(0, currentData.Length, delegate(int i)
{
   // ...
});

​​ . .

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Answer 2

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Answer 3

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