This is what the DirectX documentation says about it:
Quote:


D3DTOP_DOTPRODUCT3
Modulate the components of each argument as signed components, add their products; then replicate the sum to all color channels, including alpha. This operation is supported for color and alpha operations.
S_rgba = (Arg1_r*Arg2_r+Arg1_g*Arg2_g+Arg1_b*Arg2_b)




You can find all parameters for ColorOp if you look for this keyword: D3DTEXTUREOP

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