fix(opstack): two cell-sweep pads assumed MinRadius <= MaxRadius; a third already didn't
Second defect from the full 28-op EffectOverBox audit. Three ops roll a radius as Lerp(MinRadius, MaxRadius, hash01), which lands in [min(A,B), max(A,B)] -- Lerp does not require A <= B. Their EffectOverBox sweeps lattice cells padded by the largest radius a cell could hold, so a pad below the true maximum means the cells are never examined and the op reports Identity for a box its own Eval will fill or carve: no geometry, no collision. FGridColumnMod ~1086 Max(MaxRadius, 0) exposed FShaftFieldSource ~1436 Max(ShaftMaxRadius, ConnectorRadius) exposed FIslandBlobSource ~1803 Max(IslandMinRadius, IslandMaxRadius) already correct The third one is the argument: the concern was met and guarded once in this same file, and the other two shipped without it. Fixed with FMath::Max3, a spelling already used here (~2481) and in VoxelCaveMorphology.cpp. Shipped defaults are ordered correctly (2/5, 2/7, 5/11), so this is a NO-OP at defaults -- that is its acceptance signal, and any moved number means the diff did more than intended. It needs a mis-ordered asset value, which nothing prevents: ClampMin is a per-property floor and UE cannot express "<= that other property". ColumnMinRadius is also settable per-room via UVoxelTerrainOpDefinition. Deliberately NOT fixed by normalising the params: swapping the Lerp endpoints maps the same hash to a different radius, changing geometry and breaking the eight equivalence tests. Only the bound becomes conservative; Eval is byte- identical -- verified, no Eval/Roll/GetCells line in the diff. Also audited and found sound (recorded so they are not re-chased): FPassageCarveOp and the passage bounding sphere, FOriginSpineOp, FBoundarySealOp, FShaftLedgeMod, FCaveArchMod, FDomeMod. Not built -- Jahni builds. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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# Codex task 004 — two box verdicts assume `MinRadius ≤ MaxRadius`; a third one already doesn't
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**Owner:** Codex (Model Luna, xHigh) · **Orchestrator:** Claude · **Branch:** `experimental`
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**Status:** specified, not started
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**Kind:** ⚠️ **correctness of a box verdict.** Same class as task 003. Small fix, closes a class.
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---
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## Why this exists
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Three operators roll a primitive radius from a hash between two designer-set params:
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```cpp
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Out.R = FMath::Lerp(MinRadius, MaxRadius, hash01); // FGridColumnMod ~1129
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Out.R = FMath::Lerp(P.ShaftMinRadius, P.ShaftMaxRadius, hash01); // FShaftFieldSource ~1560
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Out.Rxy = FMath::Lerp(P.IslandMinRadius, P.IslandMaxRadius, hash01); // FIslandBlobSource ~1850
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```
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`FMath::Lerp(A, B, t)` with `t ∈ [0,1]` lands anywhere in `[min(A,B), max(A,B)]` — it does **not**
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require `A ≤ B`.
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Each op's `EffectOverBox` then sweeps a **range of lattice cells** around the query box, padded by
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the largest radius a cell could hold, and tests each rolled primitive exactly. The pad decides which
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cells are *looked at at all*, so a pad smaller than the true maximum radius means **cells are never
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examined**, their primitives are never tested, and the op reports `Identity` for a box that its own
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`Eval` will carve or fill.
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| op | pad used for the cell sweep | correct? |
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|---|---|---|
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| `FGridColumnMod` ~1086 | `FMath::Max(MaxRadius, 0.0f) + ColBlend` | ⛔ **exposed** |
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| `FShaftFieldSource` ~1436 | `FMath::Max(P.ShaftMaxRadius, P.ConnectorRadius) + ExtraReach` | ⛔ **exposed** |
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| `FIslandBlobSource` ~1803 | `const float MaxR = FMath::Max(P.IslandMinRadius, P.IslandMaxRadius);` | ✅ **already correct** |
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**The third one is the point.** Someone hit this exact concern while writing the island source and
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guarded it. The other two shipped without the guard. This task makes the three consistent.
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## How exploitable, stated honestly
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The shipped defaults are correctly ordered (`2/5`, `2/7`, `5/11`), so **nothing is broken out of the
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box.** It needs a mis-ordered asset value — `ColumnMinRadius = 8, ColumnMaxRadius = 4`.
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Nothing prevents that. The `UPROPERTY` metas carry `ClampMin = "1.0"`, which is a per-property
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floor; Unreal has no declarative way to say "must be ≤ that other property". And `ColumnMinRadius`
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is *also* settable per-room through `UVoxelTerrainOpDefinition`, so it is not only the strate asset.
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What makes it worth the five lines: when it does happen, the failure is **invisible and maddening**.
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`Eval` still draws the fat column perfectly, so every tile that gets meshed looks correct; only the
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tiles the classifier *skipped* are missing — no geometry, no collision, in a world that otherwise
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looks right.
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## The fix — five lines, and one thing you must NOT do
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Make each pad use the true envelope:
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```cpp
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// FGridColumnMod ~1086
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const float Reach = FMath::Max3(MinRadius, MaxRadius, 0.0f) + ColBlend;
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// FShaftFieldSource ~1436
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const float Pad = FMath::Max3(P.ShaftMinRadius, P.ShaftMaxRadius, P.ConnectorRadius) + ExtraReach;
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```
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(Use whatever spelling is idiomatic here — check that `FMath::Max3` is already used in this codebase
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before reaching for it; nested `FMath::Max` is fine and matches `FIslandBlobSource`'s existing line.)
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### ⛔ DO NOT "fix it properly" by normalising the params
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The tempting larger fix — swap `Min`/`Max` at resolution time so `Min ≤ Max` always — is **wrong and
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will break the build's tests.** `Eval` computes `Lerp(Min, Max, t)`; swapping the endpoints maps the
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same hash `t` to a *different* radius for the same cell. That changes generated geometry and breaks
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the eight bit-for-bit equivalence tests against the `switch` path.
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**Only the BOUND may become conservative. `Eval` stays byte-identical.** This is the same rule as
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task 003 and the same reason.
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## ⚠️ Invariants
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1. **No `Eval`, `RollColumn`, `RollShaft`, `GetCells`, or `GetCellsAt` body may change.** If your
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diff touches one, you have the wrong site — stop and say so.
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2. **Do not touch `FIslandBlobSource`.** It is already correct and is the reference for this fix.
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3. The change direction is strictly conservative: a wider sweep examines *more* cells, so a verdict
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can only move from `Identity` toward `CarveOnly`/`FillOnly`, never the reverse. Do not add any
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compensating tightening.
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4. Comments are French + English; match the surrounding file. Say **why** the envelope is
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`max(Min, Max)` and not `Max` — the next reader must not "simplify" it back.
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## Acceptance
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- `git diff --stat` shows exactly one file: `Source/VoxelForge/Private/VoxelDensityOpStack.cpp`,
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and a handful of lines.
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- The three ops now agree on the pattern.
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- After the build: **every box-verdict line and every equivalence test is unchanged**, because the
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shipped defaults are correctly ordered and the envelope only differs when they are not. **A change
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in any of those numbers means the diff did something it should not have.** That is this task's
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whole acceptance signal — a *no-op at defaults* is the expected, correct result.
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## Notes for the reviewer (Claude)
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- Confirm both pads changed and `FIslandBlobSource` did not.
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- Confirm no `Lerp` argument order was touched anywhere — that is the failure mode that would look
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like a tidy-up and silently change the world.
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@@ -3628,3 +3628,72 @@ The first attempt stopped without editing: my spec wrote `VF_PerlinAbsBound` in
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exactly the behaviour the spec template asks for ("if the code contradicts the spec, stop and say so
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rather than guessing"), and it is worth recording that it works — the cost was one clarification
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instead of a plausible-looking wrong rename.
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## 2026-08-16 (f) — the box-verdict audit, finished: 28 ops swept, a second class of bug found
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Having found the `ExtraReach` bug by auditing one archetype, I swept **all 28 `EffectOverBox`
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implementations** rather than stopping at the one that paid. Result: one more real defect, three
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false alarms worth recording so nobody re-chases them, and a clean bill for the rest.
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### ⛔ FOUND — `Min > Max` radius envelope (`CODEX-TASK-004`)
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Three ops roll a primitive radius as `FMath::Lerp(MinRadius, MaxRadius, hash01)`. `Lerp` with
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`t ∈ [0,1]` lands in `[min(A,B), max(A,B)]` — it does **not** require `A ≤ B`. Each op's
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`EffectOverBox` then sweeps a range of lattice cells padded by the largest radius a cell could hold;
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a pad below the true maximum means cells are **never examined**, so the op reports `Identity` for a
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box its own `Eval` will fill or carve.
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| op | pad | |
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|---|---|---|
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| `FGridColumnMod` ~1086 | `Max(MaxRadius, 0)` | ⛔ exposed |
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| `FShaftFieldSource` ~1436 | `Max(ShaftMaxRadius, ConnectorRadius)` | ⛔ exposed |
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| `FIslandBlobSource` ~1803 | `FMath::Max(IslandMinRadius, IslandMaxRadius)` | ✅ **already correct** |
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**The third is the whole argument.** Someone hit this exact concern writing the island source and
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guarded it; the other two shipped without. Fixed to `FMath::Max3(...)` — a spelling already used in
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this file (~2481) and in `VoxelCaveMorphology.cpp`.
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**Honest severity:** shipped defaults are correctly ordered (`2/5`, `2/7`, `5/11`), so nothing is
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broken out of the box, and **this fix is a no-op at defaults — that is its acceptance signal.** It
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needs a mis-ordered asset value, which nothing prevents: `ClampMin` is a per-property floor and
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Unreal cannot express "≤ that other property". `ColumnMinRadius` is also settable per-room via
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`UVoxelTerrainOpDefinition`. What makes five lines worth it is the failure *mode*: `Eval` still draws
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the fat column perfectly, so every meshed tile looks right and only the **skipped** ones are missing
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geometry and collision — invisible, and maddening to diagnose.
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⚠️ Recorded in the spec because it is the tempting wrong fix: **do not normalise the params.**
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Swapping the endpoints maps the same hash to a different radius, changing generated geometry and
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breaking the eight equivalence tests. Only the *bound* may become conservative; `Eval` stays
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byte-identical. Same rule as task 003.
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### ✅ CHECKED AND SOUND — do not re-audit these
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- **`FPassageCarveOp`** — its `Eval` reads `EvaluateModifierSDF` while its box guard asks
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`AnyPassageNearBox`; the differing nouns look like a set mismatch and are not — **both iterate the
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same `Passages` array**, "Modifier" is a legacy name. And the guard is the *same function* the
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hand-written `ClassifyTile` uses, so there is one definition, not two.
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- **The passage bounding sphere** — `BoundRadius = maxDistFromCentre + Radius + 4.0f`, and that `+4`
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**is** `PASSAGE_BLEND_RADIUS`, so "the bound already includes the blend" is true rather than
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assumed. Its per-point radii are `RadiusAt(t) = Lerp(Mouth, Mid, Sin(t·π))` with `Sin ∈ [0,1]`, so
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they never exceed `Passage.Radius = max(Mouth, Mid)` — the one place the `Min > Max` class *could*
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have bitten a shipped default, and it does not.
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- **`FOriginSpineOp` / `FBoundarySealOp`** — Z-band plus XY-circle tests against named reaches; both
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fail safe to `CarveOnly`/`FillOnly`.
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- **`FShaftLedgeMod`** — returns `FillOnly` unconditionally whenever ledges are configured, and its
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`Identity` case is exactly the early-out its `Eval` takes. Conservative by construction.
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- **`FCaveArchMod` / `FDomeMod`** — they *also* roll `Lerp(Min, Max, hash)` radii, but their
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`Identity` comes only from `VF_NoCaveOverBox` (cave-surface proximity) or the feature being off.
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**No radius envelope in their verdict ⇒ not exposed.** Checked precisely because they matched the
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pattern on a grep.
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- `FConstantFieldSource`, `FSlabVoidSource`, `FSurfaceColumnSource` — never return `Identity` at all.
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### The shape of both bugs, worth naming
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Task 003 and task 004 are the same mistake twice: **a box verdict's bound was derived from the
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parameter that reads like the maximum rather than from the actual supremum of what `Eval` produces.**
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Once it was `sup|FBM|` (assumed 1.0, proved 1.5); once it was `max radius` (assumed `MaxRadius`,
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actually `max(Min, Max)`). Both times a correct instance of the same reasoning existed **elsewhere in
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the same file** — `VF_PerlinAbsBound` for the first, `FIslandBlobSource` for the second.
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⇒ When adding a bound, the question is not "what is the max parameter" but **"what is the supremum
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of the thing `Eval` can actually produce, and where in this file has that already been worked out?"**
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@@ -1081,9 +1081,10 @@ namespace
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{
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if (ColDensity <= 0.0f || Spacing <= 0.0f) { return EVoxelOpEffect::Identity; }
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// Marge : le centre d'une colonne vit dans sa cellule, son influence porte au plus
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// MaxRadius + ColBlend. Sur-estimer coûte du CPU ; sous-estimer serait un trou.
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const float Reach = FMath::Max(MaxRadius, 0.0f) + ColBlend;
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// Marge : l'enveloppe de `Lerp(MinRadius, MaxRadius, t)` est max(MinRadius, MaxRadius),
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// pas `MaxRadius` seul si l'asset inverse les paramètres. The bound must cover both
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// endpoints; using `MaxRadius` alone would leave a hole when the asset reverses them.
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const float Reach = FMath::Max3(MinRadius, MaxRadius, 0.0f) + ColBlend;
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const int32 CX0 = FMath::FloorToInt(((float)VoxelBox.Min.X - Reach) / Spacing);
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const int32 CX1 = FMath::FloorToInt(((float)VoxelBox.Max.X + Reach) / Spacing);
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@@ -1433,7 +1434,10 @@ namespace
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// La source répond pour la paire source+carve (SIMPLIFICATION DE PHASE 1) : `CarveOnly`
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// si une primitive atteint la boîte, `Identity` sinon. `ExtraReach` couvre la rugosité
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// et le blend en aval — le sous-estimer serait un TROU.
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const float Pad = FMath::Max(P.ShaftMaxRadius, P.ConnectorRadius) + ExtraReach;
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// L'enveloppe doit couvrir les deux bornes de `Lerp(ShaftMinRadius, ShaftMaxRadius, t)`,
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// pas `ShaftMaxRadius` seul si l'asset inverse les paramètres. The bound must cover
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// both radius endpoints before adding connector and downstream reach.
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const float Pad = FMath::Max3(P.ShaftMinRadius, P.ShaftMaxRadius, P.ConnectorRadius) + ExtraReach;
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const FBox Padded = VoxelBox.ExpandBy(Pad);
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const float Spacing = FMath::Max(P.ShaftSpacing, 1.0f);
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