Angry Birds is fundamentally a rotating rigid-body stacking game, and
neither existing engine could be extended into it: PeggleLogic collides a
moving circle against static pegs with no rotation, and GooTowerLogic has
no angular state at all because its rigidity is emergent from
triangulation. Matter.js ships in the CDN Phaser build but is not
importable in bare Node and not reproducible, which would forfeit the
verifier, the generator's measured star thresholds, and the editor's
winnability gate.
AngryBirdsPhysics.js is a bespoke solver: convex polygons and circles,
uniform-grid broadphase, SAT with reference-face clipping to 2-point
manifolds, sequential impulses with warm starting keyed on stable feature
ids, Coulomb friction, split-impulse position correction, and island
sleeping.
Split impulse rather than plain Baumgarte is the load-bearing choice.
Biasing the real velocity makes penetration proportional to load, so the
bottom contact of a 10-box tower sank ~9x deeper than the top and the
stack sagged 12.85px. Correcting position through a discarded
pseudo-velocity removes a fixed fraction of the excess per substep
regardless of load; sag is now 0.46px per contact, exactly the slop band
we deliberately allow.
Gate: 10-box tower settles in 0.68s and sleeps with <1px drift and 0.35
degrees of tilt; friction holds on a 15 degree slope and slips on 40;
replay is bit-identical and frame-rate independent; 40 monkey seeds
produce no NaN, no overspeed and no sinking.
tools/verifyAngryBirds.js -> 51 checks green.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01M1wNRvLLtyfCDAET7oYouf
Playtest fixes (two reports, both bugs):
- Bad ground no longer instantly crashes: holes and obstacles only
put you down above surfaceCrashSpeed; below that you bog to a crawl
that is capped under the crash speed, always escapable
- Steep ramps (45°) no longer crash: launch lifts the bike clear of
the lip, pitch is clamped to pitchMax, and landing angle is clamped
to landGroundAngleMax so straddled cliff edges don't count as
rideable surfaces
- Harness now drives every ramp at seven speeds; no crashes allowed
Wave 5 polish:
- Scenery: infield and apron shrub rows (bush, apronBush, tuft)
transcribed from NES track maps
- Ramps given readable silhouette (packed-earth hatch, dark stroke,
lit crest, sheer-face cut)
- Gaps show infield through lane; lane dividers and cool-zone
chevrons fixed for alternating-lane contrast
- Snow and night themes retinted for visibility
- iconFrame 91 already painted
Tooling:
- Map reader masks ramp columns to avoid false mud/cool-zone detection
- All 10 track qualifyMs retuned from playtest measurements
Updated build plan and sprites docs.
Address three fidelity issues found during Brian's playtest:
- Throttle: base speed 150→175, heat now chases a target (0.5 for A, 1.0 for B)
so holding A alone settles the meter halfway without stalling.
- Turbo: overheat window extended to 6–8 seconds (heatRiseRate 1/7s), turbo speed
275→235 against 175 base (57% boost). AI rivals now use hysteresis (heatOff/
heatOn) instead of feathering around a single threshold.
- Landing: tolerance is lopsided — rear-wheel-first is safe (landCleanBack 0.45 /
landHardBack 1.20), nose-down is strict (landCleanNose 0.32 / landHardNose 0.92).
Crash rates across banks dropped from 1.3–5.9 to 0.2–3.0 per 1000px.
Other changes:
- Qualify targets: max(human × 1.06, expert × 1.12) so a perfect ride has margin.
- Fix NaN in countdown caused by renamed heatRate constant.
- Soak bands re-based; added monotonic ordering check (expert > human > steady > naive).
- Title screen now shows controls and "LAND REAR WHEEL FIRST" hint.
- All 10 track qualifyMs values retuned to new physics.
Brian Fertig