Fix B-spline curve silhouette gradients - #1906
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cc @ziyi-zhang |
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June 26, 2026 11:10
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Still has some issues at the curve openings. |
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Fixes a number of issues in the `bsplinecurve` shape plugin that made the projective integrators produce wrong boundary and interior gradients. * Store `ss.uv` in the primitive parameterization (segment-local `v`, azimuth) so that the projective integrators can reconstruct the foreground interaction through `pi.prim_uv`. * Rebuild the position/normal partials from the consistent local frame and its analytic derivatives instead of the Frenet torsion, which depends on the discontinuous third derivative and injects spurious gradients at the segment borders. * Bracket the silhouette azimuths on the full circle instead of a fixed half circle around the seed: both roots can lie on the same side, which silently dropped the boundary gradient of entire `v`-ranges of a bent tube seen head-on. * Account for the azimuthal drift of the silhouette curve in the interior pdf, and for the number of roots found by the projection. * Flip `ss.n` at concave folds so that it always points from the foreground to the background side of the image-space edge. * Recover the `v`-motion of the interaction point from the full first fundamental form instead of projecting onto `dp_dv` alone. * Keep grazing hits and the open curve ends when culling backfaces, and add the missing segment index bounds checks.
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This PR fixes bugs related to the
bsplinecurveshape plugin in connection with the projective integrator.bsplinecurveshapethat caused the projective integrator to produce wrong gradients.
its analytic derivatives instead of the Frenet torsion, which depends on
the discontinuous third derivative and injected spurious gradients at the
segment borders.
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