136 lines
5.4 KiB
Markdown
136 lines
5.4 KiB
Markdown
# Collision System Port - Status and Plan
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## Current State (2026-04-29)
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The collision system is no longer a pure placeholder and should not be treated
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as "delete everything and start over." A partial retail transition port exists:
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- `PhysicsEngine.ResolveWithTransition` is the active player movement resolver.
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- `BSPQuery` contains a partial retail-style BSP dispatcher.
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- `TransitionTypes` carries the active `SpherePath`, `CollisionInfo`,
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transition, step, contact, and partial slide logic.
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- `PhysicsDataCache` loads GfxObj, Setup, and CellStruct physics data.
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- Landblock streaming never edits the live collision world incrementally.
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`PreparedLandblockCollisionGeneration` owns an off-side cache, CellGraph,
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engine snapshot, buildings, statics, and versioned dynamic-owner refloods;
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`RuntimePhysicsState.CommitCollisionGeneration` validates freshness and
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activates the complete generation on the single update thread. A dirty live
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owner returns to the App cursor for refresh. The old generation remains
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queryable until that commit. See
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`docs/research/2026-07-31-atomic-collision-generation.md`.
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- `ShadowObjectRegistry` gives the resolver a broadphase over nearby objects.
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- `TerrainSurface` uses triangle-aware terrain contact.
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This foundation is useful, but it is not complete retail collision parity.
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The project now tracks the remaining work as Phase L.2 - Movement & Collision
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Conformance:
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- Plan: `docs/plans/2026-04-29-movement-collision-conformance.md`
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- Roadmap owner: `docs/plans/2026-04-11-roadmap.md`
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- Tactical follow-ups: `docs/ISSUES.md` #30-#34
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## Durable Lesson
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Do not guess at AC physics, movement packets, terrain/cell ownership, or
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collision constants. The previous patchwork failures came from simplified
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approximations:
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- static overlap instead of swept-sphere transition behavior
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- custom object collision instead of retail `CSphere` / `CCylSphere`
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- incomplete BSP dispatch
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- ad-hoc push-out instead of retail slide / edge / precipice handling
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- server "no rubber-band" treated as proof of local collision correctness
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The named retail decomp is now the primary source. Search
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`docs/research/named-retail/acclient_2013_pseudo_c.txt` by `class::method`
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before using older decompiled chunks or reference repos.
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## Active Approach
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Continue by conformance lanes rather than rewriting blindly:
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1. **Truth & diagnostics (L.2a).** Add local placement/contact/cell,
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object-hit, outbound-packet, server echo, and correction-delta probes.
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2. **Movement wire/contact authority (L.2b).** Fix contact byte and full-cell
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truth before using ACE acceptance as evidence.
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3. **Transition parity (L.2c).** Port edge-slide, cliff-slide,
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precipice-slide, step-up/down slide, and `NegPolyHit` dispatch.
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4. **Shape fidelity (L.2d).** Finish `CSphere` / `CCylSphere` semantics,
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live-entity shapes, and building object identity.
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5. **Cell ownership (L.2e).** Port `CELLARRAY`, `find_cell_list`,
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`check_other_cells`, `adjust_check_pos`, low-cell updates, and `cell_bsp`.
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6. **Real-DAT and live observer conformance (L.2f).** Promote every synthetic
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case to real-world fixtures and retail-observer checks.
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## What To Preserve
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- `CollisionPrimitives.cs` low-level helpers, while auditing remaining shape
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gaps against named retail.
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- `PhysicsDataCache.cs` DAT-backed collision data loading.
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- `ShadowObjectRegistry.cs` broadphase concept.
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- `TransitionTypes.cs` data structures and partial transition port.
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- `BSPQuery.cs` partial dispatcher as the current porting surface.
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- `PhysicsBody.cs`, `MotionInterpreter.cs`, and `PlayerWeenie.cs` foundations.
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## Known Gaps
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- Full `CELLARRAY` and adjacent-cell ownership are missing.
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- `cell_bsp` is not yet a first-class runtime owner.
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- Building portal transit and building entry/exit collision are incomplete.
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- `edge_slide`, `cliff_slide`, `precipice_slide`, and `NegPolyHit` behavior are
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incomplete.
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- Live entity shape fidelity is simplified.
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- Outbound movement contact/cell fields can be overconfident.
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- Routine local/server correction diagnostics are missing.
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## Retail Anchors
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Primary:
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- `docs/research/named-retail/acclient_2013_pseudo_c.txt`
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- `docs/research/named-retail/acclient.h`
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- `docs/research/named-retail/symbols.json`
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Key names:
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- `CTransition::find_transitional_position`
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- `CTransition::transitional_insert`
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- `CTransition::step_up`
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- `CTransition::step_down`
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- `CTransition::edge_slide`
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- `CTransition::cliff_slide`
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- `SPHEREPATH::step_up_slide`
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- `SPHEREPATH::precipice_slide`
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- `SPHEREPATH::adjust_check_pos`
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- `CTransition::check_other_cells`
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- `CObjCell::find_cell_list`
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- `CPhysicsObj::is_valid_walkable`
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- `CBuildingObj::find_building_collisions`
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- `CCellStruct::sphere_intersects_cell`
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- `CCylSphere::intersects_sphere`
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- `CSphere::intersects_sphere`
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- `CSphere::slide_sphere`
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Older fallback:
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- `docs/research/decompiled/chunk_00530000.c`
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- `docs/research/decompiled/chunk_00500000.c`
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- `docs/research/acclient_function_map.md`
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Reference aids:
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- `references/ACE/Source/ACE.Server/Physics/`
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- `references/holtburger/` for movement wire behavior
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- `references/AC2D/` for the older client-side movement packet reference
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## Mandatory Workflow
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For every AC-specific function:
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1. Grep named retail first.
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2. Cross-reference ACE / holtburger / AC2D where relevant.
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3. Write readable pseudocode before porting.
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4. Port faithfully; do not simplify.
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5. Add conformance tests.
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6. Integrate surgically into the active L.2 lane.
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7. Verify with synthetic tests, real-DAT fixtures, and live observer evidence.
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