FA-87245 / Physics integrator stability / Member archive

Linear damping uses the explicit 1 - c*dt factor · case 05

High damping at coarse steps flips the velocity sign and the body jitters.

Member previewVariant 5 · 3 implementations · 8 checks per implementation

Case contract

solve(v, omega, lin_damp, ang_damp, dt, max_speed, sleep_lin, sleep_ang, sleep_time, kicks): per frame, a sleeping body wakes (timer reset) only when that frame's kick is nonzero, else it is skipped. Add the kick [dvx,dvy,domega], damp with 1/(1+dt*c) (linear and angular coefficients), clamp speed magnitude, then accumulate sleep time while |v|<sleep_lin and |omega|<sleep_ang (else reset). When timer>=sleep_time the body sleeps and velocities are zeroed. Return [vx, vy, omega, timer, asleep, frame index slept or -1].

Why this case matters

Game and robotics physics loops depend on integrator update order, step control and stabilization terms; a wrong decision point turns a stable simulation into drifting or exploding motion.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
case 0	`[0.037109, -0.007539, 2.11515, 0.0, false, -1]`	`[-0.279632, 0.133877, 2.11515, 0.0, false, -1]`	Failed

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