fix(camera): #38 render-interpolate player motion
Keep local physics authoritative at the retail 30 Hz MinQuantum, but expose a render-only position that lerps between completed physics ticks for the player mesh and chase-camera target. Network outbound continues to use the discrete physics position. Also make the visually confirmed #47 humanoid close-detail DIDDegrade path default-on, with ACDREAM_RETAIL_CLOSE_DEGRADES=0 left as a diagnostic opt-out. Verification: dotnet build AcDream.slnx -c Debug; focused #38 interpolation tests passed; visual confirmed smooth 2026-05-06. Full dotnet test AcDream.slnx -c Debug --no-build still has the known 8 AcDream.Core.Tests baseline failures. Co-authored-by: Codex <codex@openai.com>
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Erik
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5 changed files with 218 additions and 16 deletions
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@ -643,11 +643,13 @@ primary motion + collision resolution.
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- Verification: side-by-side vs legacy default in 2-client setup,
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identical visible behavior.
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## #38 — Chase camera + player feel "30 fps" since L.5 physics-tick gate
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## #38 — [DONE 2026-05-06 · (this commit)] Chase camera + player feel "30 fps" since L.5 physics-tick gate
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**Status:** OPEN
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**Status:** DONE
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**Severity:** MEDIUM (gameplay-feel regression; not a correctness bug)
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**Filed:** 2026-05-01
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**Closed:** 2026-05-06
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**Commit:** `(this commit)`
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**Component:** rendering / physics / camera
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**Description:** User reports that running around in third-person /
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@ -704,7 +706,8 @@ collision fixes.)
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**Acceptance:**
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- Chase-camera run-around at 60+ FPS feels as smooth as render rate
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suggests (no perceptual stepping)
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suggests (no perceptual stepping) — user visually confirmed
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2026-05-06.
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- Network outbound (MoveToState / AutonomousPosition cadence + values)
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unchanged from current behavior
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- Collision behavior unchanged (the L.5 wedge / steep-roof scenarios
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@ -1360,10 +1363,11 @@ If hypothesis (a) is correct, this issue effectively rolls into **#28** — the
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---
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## #47 — [DONE 2026-05-06] Humanoid Setup 0x02000001 renders bulky / lacks shape detail vs retail
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## #47 — [DONE 2026-05-06 · 0bd9b96] Humanoid Setup 0x02000001 renders bulky / lacks shape detail vs retail
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**Status:** DONE (commit pending)
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**Status:** DONE
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**Closed:** 2026-05-06
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**Commit:** `0bd9b96`
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**Severity:** MEDIUM (cosmetic — characters readable but visibly different from retail)
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**Filed:** 2026-05-06
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**Component:** rendering / mesh / character animation
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@ -1382,10 +1386,10 @@ Concrete swaps the resolver now performs:
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- Heritage variants: `0x010004BF → 0x010017A8`, `0x010004BD → 0x010017A7`,
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`0x010004B7 → 0x0100179A`, etc.
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Fix landed as `GfxObjDegradeResolver`, gated behind
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`ACDREAM_RETAIL_CLOSE_DEGRADES=1` and scoped to humanoid setups
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(34-part with ≥8 null-sentinel attachment slots). User confirmed
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visually 2026-05-06.
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Fix landed as `GfxObjDegradeResolver`, default-on and scoped to humanoid
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setups (34-part with ≥8 null-sentinel attachment slots). Set
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`ACDREAM_RETAIL_CLOSE_DEGRADES=0` only for diagnostic before/after
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comparisons. User confirmed visually 2026-05-06.
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Files: `src/AcDream.Core/Meshing/GfxObjDegradeResolver.cs`,
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`src/AcDream.App/Rendering/GameWindow.cs` (wiring), 5 unit tests in
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@ -0,0 +1,98 @@
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# Issue #38 render interpolation pseudocode
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## Problem
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Phase L.5 correctly restored retail's `CPhysicsObj::update_object`
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physics gate: the body only integrates when accumulated frame time reaches
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`PhysicsBody.MinQuantum` (1/30 second). That keeps collision behavior aligned
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with retail, but the renderer currently reads `_body.Position` directly.
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At 60+ FPS that means several rendered frames can show the same physics
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position, then jump to the next 30 Hz position. Chase camera makes the stepping
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obvious because both the player mesh and camera target follow that discrete
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physics sample.
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## Evidence
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- Named retail: `CPhysicsObj::update_object` at `0x00515d10`
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(`docs/research/named-retail/acclient_2013_pseudo_c.txt:283950`) skips or
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consumes time outside the valid quantum window and calls
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`CPhysicsObj::UpdateObjectInternal` only for accepted physics quanta.
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- ACE mirrors the same constants in `PhysicsGlobals`: `MinQuantum = 1/30`,
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`MaxQuantum = 0.1`, `HugeQuantum = 2.0`.
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- ACE's `InterpolationManager` / `PositionManager` prove client-style
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smoothing is a known AC-family concept, but their queue chases network target
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positions. Issue #38 is narrower: local render-only interpolation between the
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last two authoritative local physics ticks.
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- Glenn Fiedler's "Fix Your Timestep!" describes the canonical fixed-timestep
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accumulator plus render interpolation pattern:
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https://gafferongames.com/post/fix_your_timestep/
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## Intentional divergence
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Retail did not need a separate high-FPS render interpolation layer because the
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2013 client effectively presented near the same cadence as its physics gate.
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acdream renders at modern display rates, so we preserve retail's 30 Hz physics
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truth but draw a blended visual position between the last two physics truths.
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## Pseudocode
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State stored by `PlayerMovementController`:
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```text
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physicsAccum: leftover render time not yet consumed by physics
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prevPhysicsPos: body position at the start of the most recently completed tick
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currPhysicsPos: body position at the end of the most recently completed tick
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```
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On spawn, teleport, or any authoritative SetPosition:
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```text
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body.Position = newPosition
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prevPhysicsPos = newPosition
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currPhysicsPos = newPosition
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physicsAccum = 0
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```
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Each Update(dt):
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```text
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physicsAccum += dt
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if physicsAccum > HugeQuantum:
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physicsAccum = 0
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prevPhysicsPos = body.Position
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currPhysicsPos = body.Position
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return/render body.Position
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if physicsAccum >= MinQuantum:
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oldTickEnd = currPhysicsPos
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preIntegratePos = body.Position
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tickDt = min(physicsAccum, MaxQuantum)
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calc_acceleration()
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UpdatePhysicsInternal(tickDt)
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postIntegratePos = body.Position
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resolve collision from preIntegratePos to postIntegratePos
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body.Position = resolved physics position
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update contact/cell/velocity exactly as before
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prevPhysicsPos = oldTickEnd
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currPhysicsPos = body.Position
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physicsAccum -= tickDt
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alpha = clamp(physicsAccum / MinQuantum, 0, 1)
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renderPosition = lerp(prevPhysicsPos, currPhysicsPos, alpha)
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```
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Important constraints:
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- Never write `renderPosition` back to `_body.Position`.
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- `MovementResult.Position` remains the authoritative physics/collision/network
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position.
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- Add `MovementResult.RenderPosition` for mesh and camera drawing only.
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- Outbound `MoveToState` / `AutonomousPosition` keep using
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`MovementResult.Position`.
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- If no physics tick has completed yet, `prevPhysicsPos == currPhysicsPos`, so
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interpolation is a no-op.
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