Swept-AABB broadphase for the SDF collision sequence error function#1527
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Swept-AABB broadphase for the SDF collision sequence error function#1527cdtwigg wants to merge 2 commits into
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Summary: Add `SDFCollisionSequenceErrorFunctionT`, a two-frame `SequenceErrorFunctionT` that penalizes a vertex sweeping through an SDF collider between consecutive frames. The single-frame `SDFCollisionErrorFunctionT` only sees penetration at the sampled poses, so a vertex moving fast enough to pass entirely through a thin collider (a finger, say) in one timestep is never penalized — it tunnels. This closes that gap for the sequence solver, which is used to post-process existing motion. How it works: - For each participating vertex, the segment connecting its position at frame t and t+1 is swept against each collider in the collider's local SDF frame: each endpoint is mapped through its own frame's world-to-collider transform and the two local positions are interpolated linearly. This captures the relative motion when both vertex and collider are joint-driven, keeps the interpolation exactly differentiable (no slerp-derivative approximation), and makes the sphere-trace that locates surface crossings exactly conservative (distances and steps are in the same local units, so a thin feature can't be stepped over). - The penalty is `w * phiMax^2` per penetrating sub-interval, where `phiMax` is the greatest penetration depth reached along the sweep. It is a max, not an integral, so it depends only on how deep the pass-through gets, never on how long the segment stays inside (no degenerate "stretch the trajectory to dilute the penalty" direction). The deepest point is located exactly by bisecting `d'(s) = 0`; because it is a true interior extremum, the envelope theorem makes the gradient independent of how the deepest point drifts with the parameters, so it reduces to the single-frame contact gradient evaluated there, split across the two frames by the interpolation weights `(1 - s*)` and `s*`. One residual per interval; gradient and Jacobian both finite-difference clean. - Only sub-intervals bounded by two real surface crossings (entry and exit) are penalized, targeting the pure pass-through case and leaving at-frame penetration to the per-frame error function. - Derivatives reuse the shared `detail_sdf_collision` chain-rule helpers from the previous diff, evaluated against both frames' skeleton states. The local SDF gradient is mapped to world space including the world-to-collider scale factor, which the derivatives require whenever the collider's joint carries a non-unit scale. The penetration normal is treated as frozen per evaluation (the standard Gauss-Newton contact linearization), so no SDF second derivatives are needed — only transform derivatives, which the shared helpers already provide. Known limitation / follow-up: a vertex passing exactly through a collider's medial axis (dead-center through the axis of a thin tube, or perpendicular through a thin sheet) lands on a degenerate point where the SDF normal is undefined and the depth has a non-smooth maximum, so the gradient there is ~0 and gives no signal. This is a measure-zero case for convex colliders (any off-axis pass resolves correctly by deflection); a retract-along-the-entry-normal fallback for it is a planned follow-up. There is also no broadphase culling yet (every participating vertex is swept against every collider) and no pymomentum binding (the single-frame function has one). Reviewed By: yutingye Differential Revision: D108807348
Summary: Add a conservative broadphase to `SDFCollisionSequenceErrorFunctionT` that skips any (vertex, collider) pair whose swept segment cannot reach the collider. The segment is already mapped into the collider's local SDF frame for the sweep; if the segment's local axis-aligned bounding box does not overlap the collider's SDF `bounds()`, the pair cannot penetrate and is skipped before the more expensive sphere-trace and deepest-point search. Because both the cull and the detailed test operate in the same local frame, the cull is exact — it only ever skips pairs whose detailed test would have found no penetration — so the error, gradient, and Jacobian are unchanged. This replaces running the sphere-trace for every (vertex, collider) pair regardless of proximity, which matters once the participating-vertex set or collider count is large. It adds `bounds()` to the (already duck-typed) collider interface this function relies on. Reviewed By: yutingye Differential Revision: D108807344
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…1527) Summary: Add a conservative broadphase to `SDFCollisionSequenceErrorFunctionT` that skips any (vertex, collider) pair whose swept segment cannot reach the collider. The segment is already mapped into the collider's local SDF frame for the sweep; if the segment's local axis-aligned bounding box does not overlap the collider's SDF `bounds()`, the pair cannot penetrate and is skipped before the more expensive sphere-trace and deepest-point search. Because both the cull and the detailed test operate in the same local frame, the cull is exact — it only ever skips pairs whose detailed test would have found no penetration — so the error, gradient, and Jacobian are unchanged. This replaces running the sphere-trace for every (vertex, collider) pair regardless of proximity, which matters once the participating-vertex set or collider count is large. It adds `bounds()` to the (already duck-typed) collider interface this function relies on. Reviewed By: yutingye Differential Revision: D108807344
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Summary:
Add a conservative broadphase to
SDFCollisionSequenceErrorFunctionTthat skips any (vertex, collider) pair whose swept segment cannot reach the collider. The segment is already mapped into the collider's local SDF frame for the sweep; if the segment's local axis-aligned bounding box does not overlap the collider's SDFbounds(), the pair cannot penetrate and is skipped before the more expensive sphere-trace and deepest-point search. Because both the cull and the detailed test operate in the same local frame, the cull is exact — it only ever skips pairs whose detailed test would have found no penetration — so the error, gradient, and Jacobian are unchanged.This replaces running the sphere-trace for every (vertex, collider) pair regardless of proximity, which matters once the participating-vertex set or collider count is large. It adds
bounds()to the (already duck-typed) collider interface this function relies on.Reviewed By: yutingye
Differential Revision: D108807344