[freezy]

Ports physics fixes Visual Pinball made in the last weeks (mostly its FIX_PHYSICS path, which is enabled in VPX) that VPE didn't have yet. One commit per area:

• Wall touch band (vpinball#4088): slow touches inside a line segment's touch band got a remapped hit time that never fits a step, so they were dropped. They are contacts now.
• Contact friction (vpinball#4086, #4088, 8c4cf05d): mass-independent normal force and surface acceleration, friction cone bounded by the contact's own normal impulse instead of gravity alone (nothing on walls and the glass), the 0.025 static gate restricted to supports (it always picked static friction on walls), and the full slip-removing impulse instead of a step-length fraction of it.
• Flipper contact (vpinball#4053, 8c4cf05d): static friction inertia sign, and the gap acceleration uses the ball's center, so a spinning ball keeps its support.
• Flipper inertia (a75d4da2d): moment of inertia of the real flipper shape, coil torque rescaled so the free swing stays the one tables are tuned on.
• Ball/ball collision normal (vpinball#4051): taken between both centers at hit time.
• Ball/ball resting contacts (vpinball#4087, #4088, 8c4cf05d): ball pairs were never contacts, so resting balls kept colliding and popping apart. Contacts with relative approach and friction, inelastic slow impacts, ball contacts resolved first and static contacts cancelling what earlier contacts did to the ball (stack and row jitter, Newton's cradle).
• Ramp entrance (vpinball#4079): the start edge had its joint twice.
• Reversed winding (vpinball#4085 and follow-ups): walls drawn clockwise collide from both sides like in VPX, and get their top back (the ear clipping found no triangles, so the top collider was missing and collider generation threw). Curved triggers no longer swap hit and unhit.
• Playfield (8c4cf05d): a slow ball embedded deeper than the touch layer collides instead of sinking through.

Where VPE differs from VPX on purpose:

• Static contact friction works from a snapshot of the ball's motion taken before the contact pass (so it doesn't take another contact's normal response as slip). With VPX's full slip-removing impulse, each later contact of a ball now sees the friction of the earlier ones, or two contacts sharing a slip would both remove it. Spring hinges are left out, they recompute their normal. Ball/ball contacts use the live motion of both balls, as in VPX.
• The bnd > -PHYS_TOUCH limit on triangle contacts from 8c4cf05d is not ported: as a collision, a cover embedded in the ball from above would get the displacement correction pushing the ball into the floor again. VPE's contact recovery, which never pushes along gravity, handles deep triangle contacts.
• VPX's small overlap drain is applied to ball/ball contacts only. VPE's static contacts keep their own recovery.
• A ball/ball contact cancels at most the pair's own approach plus a step of load: VPX braked the trailing one of two balls moving together.
• A static contact may take back an earlier contact's lift that is larger than the step's load (short steps), and passes the take-back on so two supports don't take it twice.

Tests: new PhysicsAlignmentTests (38 cases, several ported from VPX's test-physics-defects.cpp). The EditMode suite has no new failures compared to master; the 43 failures on master (mesh Z offsets, VPX write float noise, play-mode fixtures, Kiki ABI) are unchanged. Not play-tested on a table yet.

[greptile-apps]

Confidence Score: 5/5

[High impact] The PR appears safe to merge; the previous floor-support issue is fixed, and no new blocking issue was found.

Summary

Ports recent Visual Pinball physics fixes and adds regression tests.

• Slow ball pairs settle into contacts and pass momentum along.
• Surface contacts use their own load to set friction.
• Slow wall touches and embedded playfield balls enter the right response path.
• Flippers keep spinning balls supported and use their real shape for inertia.
• Reversed outlines keep their wall tops and trigger sides.
• Ramp entrance joints are added once when collider edges are built.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart TD
  A[Find hits and contacts] --> B[Put ball contacts first]
  B --> C[Resolve collisions]
  C --> D[Save support from static impacts]
  D --> E[Prepare contacts and mark backing support]
  E --> F[Resolve ball contacts once per pair]
  F --> G[Pass both balls' changes to later contacts]
  G --> H[Resolve static contacts]

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_{Reviews (4) · Last reviewed commit: "physics: preserve backing support for ba..." · Reviewed by Greptile}