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test: fix the ULP yardstick — it measured output density, not where the error is born

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The tuned pass warned: 121/20000 differ, 6 over the bound, worst 1.72e-05, still 0
isosurface crossings. The port is fine; the bound was wrong.

It was 16 * max(|Old|, 1) * FLT_EPSILON — ULPs on the OUTPUT density. But density is
min(Z - Floor, Ceil - Z), so near the isosurface the output tends to 0 while the
intermediates are in the hundreds. Rounding born at scale ~400 judged against a
yardstick of scale 1: 400x too tight, and tightest exactly where the test looks
hardest. Large amplitudes are what expose it, which is why the tuned pass earned
its place immediately.

Measured rather than assumed: amplitudes rose x2.25-3.33 and the deltas rose x4.5,
with the worst delta at 0.345 ULP of |Z| — sub-ULP at the scale it is born in. Error
proportional to amplitude is ordinary rounding. A wrong noise offset or a missing
abs() would move the surface by voxels, four orders of magnitude above this.

The bound now scales with max(|Old|, |Z|, strate Z bounds), and the warning prints
the discriminator instead of just the alarm: the density at the offending sample and
the delta in ULPs of the working scale. A few ULP at near-zero density is
cancellation; thousands is drift. That distinction is now readable rather than
re-derivable at a build apiece.

The box verdicts held under the worst case: 32/60 proved uniform, 0 unsound, under
tripled ceiling roughness and 3x the columns — exactly the case that stresses the
Max(CeilZ - noise, FloorSurface + 2) clamp.

Also recorded in DECOMPOSITION section 3: FlatPlain and CrystalChamber render
identical in the live world because nothing in the content distinguishes them. The
merge loses no distinction; it reveals there was none.

UNVERIFIED: the corrected bound.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
This commit is contained in:
Fr0zka
2026-07-27 15:39:03 +02:00
parent 85993199fb
commit 51d8db842b
3 changed files with 147 additions and 17 deletions
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Source/VoxelForge/Private/Tests/VoxelForgeOpStackSlabTest.cpp
+69 -17
View File
@@ -128,8 +128,38 @@ bool FVoxelForgeOpStackSlabTest::RunTest(const FString& Parameters)
//=====================================================================
// 1. ÉQUIVALENCE — géométrie d'abord, bits ensuite.
//=====================================================================
// ─────────────────────────────────────────────────────────────────────
// LE BON MÈTRE — corrigé 2026-07-27 après que la passe `tuned` a crié au loup
// ─────────────────────────────────────────────────────────────────────
// Première version : `16 · max(|Old|, 1) · FLT_EPSILON`, c.-à-d. l'ULP mesuré sur la
// DENSITÉ DE SORTIE. C'est le mauvais mètre, et il se trompe exactement là où le test
// regarde le plus : la densité vaut `min(Z - Sol, Plafond - Z)`, donc PRÈS DE L'ISOSURFACE
// la sortie tend vers 0 pendant que les intermédiaires (surfaces, Z monde, amplitudes de
// bruit) valent des CENTAINES. Un arrondi né à l'échelle 400 était jugé contre un mètre
// à l'échelle 1 — 400× trop serré.
//
// Mesuré : la passe `tuned` (rugosités ×2.25 et ×3.33) a vu ses écarts croître ×4.5, et
// son pire écart valait **0.345 ULP de |Z|**. Sous-ULP à l'échelle où l'erreur naît.
// L'erreur est donc proportionnelle à l'AMPLITUDE, ce qui est la signature d'un arrondi
// ordinaire, pas d'une transcription fausse.
//
// Le mètre correct est la magnitude des quantités D'OÙ VIENT l'erreur. Le test reste
// discriminant : une vraie dérive de portage (offset de bruit faux, `abs()` manquant,
// clamp oublié) déplace la surface de plusieurs VOXELS — 4 ordres de grandeur au-dessus
// de ce seuil, pas 4 fois.
//
// The first yardstick measured ULPs on the OUTPUT density, which tends to 0 near the
// isosurface while the intermediates are in the hundreds. Rounding born at scale ~400 was
// judged against a yardstick of scale 1. Real port drift moves the surface by voxels —
// four orders of magnitude above this bound, so the test stays discriminating.
const float SurfaceScale = FMath::Max(FMath::Abs(SlabParams.StrateTopWorldZ),
FMath::Abs(SlabParams.StrateBottomWorldZ));
int32 NumDiff = 0, WorstIdx = -1, NumBeyondUlpNoise = 0, NumSolidDisagreements = 0;
float WorstDelta = 0.0f;
float WorstDelta = 0.0f, WorstOld = 0.0f, WorstUlpsOfScale = 0.0f;
// Le pire cas PARMI LES DÉPASSEMENTS — c'est lui qui dit si un WARN est du bruit ou une dérive.
float WorstOutlierDelta = 0.0f, WorstOutlierOld = 0.0f, WorstOutlierUlps = 0.0f;
for (int32 i = 0; i < NumSlabSamples; ++i)
{
const float X = (float)Points[i].X, Y = (float)Points[i].Y, Z = (float)Points[i].Z;
@@ -141,13 +171,26 @@ bool FVoxelForgeOpStackSlabTest::RunTest(const FString& Parameters)
{
++NumDiff;
const float Delta = FMath::Abs(Old - New);
if (Delta > WorstDelta) { WorstDelta = Delta; WorstIdx = i; }
// Même forme que le carve de Maze : `(ColBlend - ColumnSDF)` annule au bord de la
// coquille de blend des colonnes, donc un ULP amont ressort amplifié. Marge
// généreuse mais BORNÉE — au-delà, c'est une vraie dérive de portage.
const float UlpNoise = 16.0f * FMath::Max(FMath::Abs(Old), 1.0f) * FLT_EPSILON;
if (Delta > UlpNoise) { ++NumBeyondUlpNoise; }
// L'échelle à laquelle CET échantillon calcule : la sortie, sa propre altitude, et
// les bornes de la strate. C'est le plus grand des trois qui porte l'arrondi.
const float Scale = FMath::Max3(FMath::Abs(Old), FMath::Abs(Z),
FMath::Max(SurfaceScale, 1.0f));
const float Ulps = Delta / (Scale * FLT_EPSILON);
if (Delta > WorstDelta)
{
WorstDelta = Delta; WorstIdx = i; WorstOld = Old; WorstUlpsOfScale = Ulps;
}
if (Delta > 16.0f * Scale * FLT_EPSILON)
{
++NumBeyondUlpNoise;
if (Delta > WorstOutlierDelta)
{
WorstOutlierDelta = Delta; WorstOutlierOld = Old; WorstOutlierUlps = Ulps;
}
}
}
// Le mesher ne lit que le SIGNE. Un désaccord de CÔTÉ bouge la géométrie.
if ((Old >= 0.0f) != (New >= 0.0f)) { ++NumSolidDisagreements; }
@@ -161,23 +204,32 @@ bool FVoxelForgeOpStackSlabTest::RunTest(const FString& Parameters)
else if (NumBeyondUlpNoise == 0)
{
AddInfo(FString::Printf(
TEXT("%s: %d of %d samples differ, ALL at ULP scale (largest |delta| %.9g at ")
TEXT("(%.0f, %.0f, %.0f)), and 0 cross the isosurface. Same accepted floor as Maze ")
TEXT("-- see AUDIT-2026-07.md C10 before hunting it."),
SlotName, NumDiff, NumSlabSamples, WorstDelta,
TEXT("%s: %d of %d samples differ, ALL at ULP scale (largest |delta| %.9g = %.3f ULP ")
TEXT("of the working scale, where density = %.6g, at (%.0f, %.0f, %.0f)), and 0 cross ")
TEXT("the isosurface. Same accepted floor as Maze -- see AUDIT-2026-07.md C10."),
SlotName, NumDiff, NumSlabSamples, WorstDelta, WorstUlpsOfScale, WorstOld,
WorstIdx >= 0 ? Points[WorstIdx].X : 0.0f,
WorstIdx >= 0 ? Points[WorstIdx].Y : 0.0f,
WorstIdx >= 0 ? Points[WorstIdx].Z : 0.0f));
}
else
{
// Le message porte maintenant LE DISCRIMINANT, pas seulement l'alarme : la densité au
// point fautif et l'écart exprimé en ULP de l'échelle de travail. Un dépassement à
// quelques ULP avec une densité proche de 0 est un artefact de mètre ; un dépassement
// à des milliers d'ULP est une vraie dérive. La différence se lit, elle ne se devine pas.
AddWarning(FString::Printf(
TEXT("%s: %d of %d samples differ and %d are TOO LARGE to be the accepted ULP floor ")
TEXT("(largest |delta| %.9g at (%.0f, %.0f, %.0f)); %d cross the isosurface. THIS is ")
TEXT("real port drift. Check, in order: the floor/ceiling noise offsets (7.3/11.1 and ")
TEXT("17.3+1000/19.7+2000/3000), the abs() on the ceiling noise, the ceiling clamp ")
TEXT("(FloorSurface + 2), the column blend (2.0) and the 0.15/0.7 jitter."),
SlotName, NumDiff, NumSlabSamples, NumBeyondUlpNoise, WorstDelta,
TEXT("%s: %d of %d samples differ and %d exceed the ULP bound. Worst OUTLIER: ")
TEXT("|delta| %.9g = %.1f ULP of the working scale, where density = %.6g. ")
TEXT("(Worst overall: |delta| %.9g at (%.0f, %.0f, %.0f).) %d cross the isosurface. ")
TEXT("READ THE ULP FIGURE BEFORE INVESTIGATING: a few ULP with a near-zero density is ")
TEXT("cancellation near the isosurface, not drift. Thousands of ULP IS drift -- check, ")
TEXT("in order: the floor/ceiling noise offsets (7.3/11.1 and 17.3+1000/19.7+2000/3000), ")
TEXT("the abs() on the ceiling noise, the ceiling clamp (FloorSurface + 2), the column ")
TEXT("blend (2.0) and the 0.15/0.7 jitter."),
SlotName, NumDiff, NumSlabSamples, NumBeyondUlpNoise,
WorstOutlierDelta, WorstOutlierUlps, WorstOutlierOld,
WorstDelta,
WorstIdx >= 0 ? Points[WorstIdx].X : 0.0f,
WorstIdx >= 0 ? Points[WorstIdx].Y : 0.0f,
WorstIdx >= 0 ? Points[WorstIdx].Z : 0.0f,