I made this basic Plane struct which I use for my planes now.
It seems to work fine as I am using it, but I don't use all the functions.
I think it has most plane related functionality, but I will need someone with better math skills than me to implement the Transform and IntersectLine functions, and perhaps expand it with more functions if I missed any.
But hopefully this can serve as some basis for a Plane struct for OpenTK.
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Fixed a small bug where I forgot to normalize the D attribute of the Plane. Attached the fixed version.
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