6c618937cb
Document current state (patchwork ~60-70%) and plan for clean port from ACE's complete C# implementation. Lists all 12 files to port, what to keep vs replace, and the correct approach. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
96 lines
4.5 KiB
Markdown
96 lines
4.5 KiB
Markdown
# Collision System Port — Status and Plan
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## Current State (2026-04-14)
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The collision system has been patched multiple times but does NOT match
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retail. The user has explicitly requested a **full faithful port** of
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the retail collision system — no shortcuts, no simplifications.
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## What Went Wrong
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Instead of porting the decompiled code line-by-line (as CLAUDE.md
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mandates), I wrote simplified approximations:
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- Static overlap instead of swept-sphere FindTimeOfCollision
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- Custom FindObjCollisions instead of porting Sphere.IntersectsSphere
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- Custom BSP query instead of porting BSPTree.find_collisions dispatcher
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- Ad-hoc push-out instead of proper SlideSphere crease-projection
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- Incremental patches that don't address root architectural issues
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Each patch fixed one symptom but introduced new edge cases. The result
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is a patchwork that handles ~60-70% of cases but fails on the rest.
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## What Must Happen Next
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**Delete the existing collision code and start fresh.** Port from ACE's
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complete C# implementation, cross-referencing the decompiled code for
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ground truth. ACE has the ENTIRE system already in C#:
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### Files to port from ACE (in order):
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1. **Sphere.cs** — `IntersectsSphere` (FUN_005387c0), `SlideSphere` (both variants), `StepSphereUp`, `StepSphereDown`, `LandOnSphere`, `CollideWithPoint`, `CollidesWithSphere`
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2. **BSPTree.cs** — `find_collisions` (6-path dispatcher)
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3. **BSPNode.cs** — `sphere_intersects_poly` (tree traversal with movement), `find_walkable`, `hits_walkable`, `sphere_intersects_solid`
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4. **BSPLeaf.cs** — leaf-level polygon tests
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5. **Polygon.cs** — `pos_hits_sphere`, `adjust_sphere_to_plane`, `check_walkable`
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6. **Transition.cs** — `FindTransitionalPosition`, `TransitionalInsert`, `StepUp`, `StepDown`, `ValidateTransition`, `AdjustOffset`
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7. **SpherePath.cs** — `SetCheckPos`, `AddOffsetToCheckPos`, `CacheLocalSpaceSphere`, `SetCollide`, `SetWalkable`, `SetNegPolyHit`
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8. **CollisionInfo.cs** — `SetContactPlane`, `SetSlidingNormal`, `SetCollisionNormal`
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9. **ObjectInfo.cs** — `ValidateWalkable`
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10. **LandCell.cs** — `FindEnvCollisions` (outdoor terrain)
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11. **EnvCell.cs** — `FindEnvCollisions` (indoor BSP)
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12. **ObjCell.cs** — `FindObjCollisions`, `find_cell_list`
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### ACE source locations:
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- `references/ACE/Source/ACE.Server/Physics/Sphere.cs`
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- `references/ACE/Source/ACE.Server/Physics/BSP/BSPTree.cs`
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- `references/ACE/Source/ACE.Server/Physics/BSP/BSPNode.cs`
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- `references/ACE/Source/ACE.Server/Physics/BSP/BSPLeaf.cs`
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- `references/ACE/Source/ACE.Server/Physics/Polygon.cs`
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- `references/ACE/Source/ACE.Server/Physics/Transition.cs`
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- `references/ACE/Source/ACE.Server/Physics/SpherePath.cs`
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- `references/ACE/Source/ACE.Server/Physics/Collision/CollisionInfo.cs`
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- `references/ACE/Source/ACE.Server/Physics/Collision/ObjectInfo.cs`
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### Decompiled ground truth:
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- `docs/research/decompiled/chunk_00530000.c` — BSP, Polygon, Sphere collision
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- `docs/research/decompiled/chunk_00500000.c` — PhysicsObj, transition callers
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- `docs/research/acclient_function_map.md` — mapped functions
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### Pseudocode (already written):
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- `docs/research/transition_pseudocode.md` — full system documented
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## What to Keep
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- `CollisionPrimitives.cs` — 9 low-level functions already faithfully ported from decompiled code. These are CORRECT and match retail.
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- `PhysicsDataCache.cs` — GfxObj/Setup/CellStruct physics data loading from dats. Correct.
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- `ShadowObjectRegistry.cs` — cell-based spatial index. Correct concept, may need refinement.
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- `TransitionTypes.cs` data structures — SpherePath, CollisionInfo, ObjectInfo, PhysicsGlobals. Mostly correct, may need field additions.
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- `PhysicsBody.cs` — Euler integration. Correct.
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- `MotionInterpreter.cs` — Motion state machine. Correct.
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- `PlayerWeenie.cs` — Run/Jump formulas. Correct.
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## What to Replace
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- `BSPQuery.cs` — replace with faithful port of BSPTree/BSPNode/BSPLeaf
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- `TransitionTypes.cs` Transition methods — replace FindTransitionalPosition, TransitionalInsert, FindEnvCollisions, FindObjCollisions, SlideSphere, AdjustOffset with faithful ports
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- `PhysicsEngine.ResolveWithTransition` — may need restructuring
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## Approach
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1. Read ACE's Sphere.cs fully (it's the object collision dispatcher)
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2. Read ACE's BSPTree.cs/BSPNode.cs/BSPLeaf.cs fully
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3. Read ACE's Transition.cs fully
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4. Port each class method-by-method, preserving ACE's logic exactly
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5. Cross-reference each method against the decompiled function address
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6. Test incrementally: terrain → indoor walls → objects → step-up → full
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