Recreating basic function in C#

Hi. **How would I go about computing the results of `UnityObjectToClipPos(foo).w` in c# for a given camera and world-space vertex?** I understand w acts as some sort of scale factor, and is used by the shader for the transformation out of homogeneous coordinates somewhere prior to the rasterization phase of a shader. For my use case it would save a lot of computational power to compute the w value for a few set points prior to the execution of the shader, rather than needing to compute those values for every vertex. Thanks!