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Fix #105467: NaN values resulting from curve editing with collision

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This was caused by an incorrect assumption in the solver:
It tries to solve both collision and length constraints simultaneously,
using the projected movement of a point as a slide direction along the surface.
This only works if the distance of the previous curve point to the surface
is less than the allowed segment length. Otherwise the segment will
exceed the allowed length even with zero slide and NaN values are computed.

The case of larger surface distance can occur if the previous segment
solve was already stretching the current segment and then the point
moves further away. In this case we can simply clamp the segment length
without violating the contact constraint.

Pull Request #105499
This commit is contained in:
Lukas Tönne
2023-03-07 11:30:07 +01:00
parent 2e5452ee87
commit e7606139ba
1 changed files with 14 additions and 5 deletions
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19
source/blender/geometry/intern/curve_constraints.cc
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@@ -146,12 +146,21 @@ void solve_length_and_collision_constraints(const OffsetIndices<int> points_by_c
float slide_direction_length_cu;
const float3 normalized_slide_direction_cu = math::normalize_and_get_length(
slide_direction_cu, slide_direction_length_cu);
const float slide_normal_length_sq_cu = math::length_squared(slide_normal_cu);
/* Use pythagorian theorem to determine how far to slide. */
const float slide_distance_cu = std::sqrt(pow2f(goal_segment_length_cu) -
math::length_squared(slide_normal_cu)) -
slide_direction_length_cu;
positions_cu[point_i] = plane_pos_cu + normalized_slide_direction_cu * slide_distance_cu;
if (pow2f(goal_segment_length_cu) > slide_normal_length_sq_cu) {
/* Use pythagorian theorem to determine how far to slide. */
const float slide_distance_cu = std::sqrt(pow2f(goal_segment_length_cu) -
slide_normal_length_sq_cu) -
slide_direction_length_cu;
positions_cu[point_i] = plane_pos_cu +
normalized_slide_direction_cu * slide_distance_cu;
}
else {
/* Minimum distance is larger than allowed segment length.
* The unilateral collision constraint is satisfied by just clamping segment length. */
positions_cu[point_i] = prev_pos_cu + math::normalize(old_pos_su - prev_pos_cu) * goal_segment_length_cu;
}
}
if (used_iterations == max_collisions) {
revert_curve = true;