Fix parameter_range() for non-clamped B-splines
#105
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The valid parameter domain for a B-spline is [knot[degree], knot[n_cv]], not [knot[0], knot[n-1]]. For example, a uniform cubic B-spline with 4 control points has knot vector [0,1,2,3,4,5,6,7]. The old code returned [0,7] but the correct valid domain is [3,4] - only the center 1/9th of the parameter space. Discovered because: this caused tessellation to generate geometry in the "phantom" outer regions, leading to overlapping patches when rendering STEP files with uniform B-spline surfaces.
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The valid parameter domain for a B-spline is [knot[degree], knot[n_cv]], not [knot[0], knot[n-1]].
For example, a uniform cubic B-spline with 4 control points has knot vector [0,1,2,3,4,5,6,7]. The existing code returned [0,7] but the correct valid domain is [3,4] - only the center 1/9th of the parameter space.
Discovered because: this caused tessellation to generate geometry in the "phantom" outer regions, leading to overlapping patches when rendering STEP files with uniform B-spline surfaces.
See two images below, this is a STEP viewer I'm working on that uses
truckfor reading/tessellation.