fix(physics, tilemap): ellipse SAT sign + stale bounds on centered level

[obiot]

Summary

Two long-standing bugs that surfaced together once a level is auto-centered (level.load on a viewport wider/taller than the map).

SAT — physics/sat.js

testEllipseEllipse and testPolygonEllipse built the relative-position vector by adding a.ancestor.getAbsolutePosition() where they should have subtracted it. Both operands resolve their world position via ancestor.getAbsolutePosition(), so the relative vector needs both terms with opposing signs.

• With ancestor.absPos == (0, 0) the wrong-sign term is zero and the bug is arithmetically invisible — every existing SAT unit test (all mocked at zero) passed.
• With a non-zero ancestor offset the circle is shifted by 2 * ancestor.absPos and ellipse-vs-anything collisions silently miss. In the platformer at a 2400×600 viewport (255 px centering), every coin / circular collider was getting "telepoted" 510 px to the right.
• The polygon/polygon path is unaffected — it builds two absolute positions and lets isSeparatingAxis do the subtraction internally.

TMX — level/tiled/TMXTileMap.js

TMXTileMap.addTo sets container.pos after adding children, so each child's cached absolute bounds (computed at addChild time) didn't include the centering offset. Children that moved on their own refreshed via the pos observer, but TMX layers, Tiled collision shapes, triggers, and decorative sprites stayed pinned at their pre-centering bounds.

• Visible as the debug overlay drawing collision shapes at the wrong screen position (the original symptom that started this investigation).
• Also broke inViewport culling for anything outside the pre-centering box.

_setBounds now walks the container subtree and refreshes absolute bounds — only when the position actually moved, so the no-op case (viewport ≤ map) skips the walk.

Tests — tests/sat.spec.js

14-case matrix over every SAT shape combination (Polygon×Polygon, Polygon×Ellipse, Ellipse×Polygon, Ellipse×Ellipse, plus circle / true-ellipse variants). Each case asserts both shift-invariance under a common ancestor offset and a near-miss geometry the buggy +offset would push out of range. Against the reverted sat.js, exactly the 9 bug-affected assertions fail; the 5 polygon-polygonized paths (true-ellipse cases that flow through testPolygonPolygon) pass — confirming the matrix tracks which SAT paths the sign error actually breaks.

Test plan

• pnpm vitest run tests/sat.spec.js — 61 / 61 pass
• Reverted sat.js, re-ran tests — 9 / 14 new ancestor-offset assertions fail, rest pass (proves the new tests bite)
• Platformer at 2400×600 viewport — coin collision now fires; debug overlay shapes land at the correct screen position
• Platformer at 1890×600 (no centering) — no regression, coins still collected

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Fixes two offset-related bugs that appear when a level/container is translated (notably TMX auto-centering when the viewport is larger than the map): SAT ellipse collision tests were computing relative positions with the wrong sign, and TMX children could keep stale absolute bounds after the parent container position changed.

Changes:

• Physics/SAT: correct relative-position computation in testEllipseEllipse and testPolygonEllipse by subtracting a.ancestor.getAbsolutePosition() instead of adding it.
• TMX: after auto-centering the level container, recursively refresh descendants’ absolute bounds so debug overlay + viewport culling use correct world-space bounds.
• Tests/Changelog: add regression tests covering non-zero ancestor offsets across SAT shape combinations and document both fixes.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
packages/melonjs/tests/sat.spec.js	Adds regression coverage ensuring SAT collision results are invariant under a shared non-zero ancestor offset (and reproduces the historical sign bug).
packages/melonjs/src/physics/sat.js	Fixes the sign error in ellipse-related SAT relative-position vectors when ancestors have non-zero absolute position.
packages/melonjs/src/level/tiled/TMXTileMap.js	Refreshes cached absolute bounds for TMX-added children after the level container is re-positioned by auto-centering.
packages/melonjs/CHANGELOG.md	Documents the SAT ancestor-offset collision fix and the TMX stale-bounds-on-centering fix.

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