How are s&t calculated on a NURBS surface?

This is a discussion on How are s&t calculated on a NURBS surface? within the Game Programming forums, part of the General Programming Boards category; Don't know how many of you deal with NURBS surfaces, but.... How are the s&t coordinates calculated on a NURBS ...

  1. #1
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    How are s&t calculated on a NURBS surface?

    Don't know how many of you deal with NURBS surfaces, but....

    How are the s&t coordinates calculated on a NURBS surface? More specifically, are they related to the knots/isoparms?

    I'm attempting to assign texture corrdinates as point attributes to the CV's of a nurb, but if I refine the nurb by adding several isoparms between two of the original (making a thick concentration of isoparms in one section), then render with a shader that bases color on the uv values I calculated, the color change gets bunched up at the point of high concentration of isoparms. If I do the same test using s&t instead of my u&v, the color changes smooth across the surface.... So I'm guessing my calculation of u&v is not like the calculation of s&t - hence the question.

  2. #2
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    I've only dealt with Total Degree Surfaces and Bi-Degree Surfaces. Of course I have dealt with B-Splines using de Boor algorithm. I don't know about NURBS surfaces but I may know someone who does. If I see him I will ask him and respond.

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