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Apply the contact cfm_factor to normal rows only, not friction tangents #26

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Apply the contact cfm_factor to normal rows only, not friction tangents #26

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14 changes: 10 additions & 4 deletions src_rbd_shaders/dynamics/multibody/contact_constraints.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -784,10 +784,16 @@ pub fn gpu_mb_solve_contact_constraints(
}

let rhs_total = j_dot_v + cons.rhs;
// CFM-factor form (rapier's `*ContactConstraintNormalPart::generic_solve`):
// `new = cfm_factor · (impulse − r · Δvel)`. `cfm_factor < 1` provides the
// soft-constraint compliance that keeps resting contacts from jittering.
let raw_imp = cons.cfm_factor * (cons.impulse - cons.inv_lhs * rhs_total);
// CFM-factor form (rapier's `ContactConstraintNormalPart::generic_solve`):
// `new = cfm_factor · (impulse − r · Δvel)`. Normal rows ONLY — rapier's
// `TangentPart::solve` takes no cfm_factor; softening friction scales the
// effective μ by cfm_factor.
let unsoft_imp = cons.impulse - cons.inv_lhs * rhs_total;
let raw_imp = if cons.kind == MB_CONTACT_KIND_TANGENT {
unsoft_imp
} else {
cons.cfm_factor * unsoft_imp
};

// Normal: clamp to ≥ 0 (no separation impulse). Friction tangent:
// clamp to `±μ · normal_impulse` — looks up the paired normal slot
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