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fix: brush-spread deposition + deposit-cap governor; retune erosion for a drainage hierarchy (terrain-water task 18)

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Deposition now spreads over the same cone brush as carving, and the per-cell
erosion ledger becomes a signed NET displacement ledger, so both caps are
measured from the height the pass found. Brush-spreading alone cut the spike
15.49 -> 6.12 m at task-17 dials, but NOT at hierarchy dials (long paths carry
far more sediment; a loaded droplet meeting a rise dumps min(rise, load) at
once -> 25.5 m). So deposition also gets governor 4, ErosionDepositCap
(default 6 m, <= 0 = unbounded), asserted on exit like the carve cap.

Dial defaults retuned for a drainage HIERARCHY: 250k droplets x 384 steps at
inertia 0.35 / evaporation 0.004, erode 0.12, carve cap 15 m. Diagnosis was
that lifetime 48 let a droplet travel at most 48 px on a ~3000 px island
radius, so paths could not overlap into trunks: the deepest task-17 features
were 43x36 px patches. Now 177 channel systems of 200+ cells at the 3 m
threshold, top one 204x279 px with 14 tributary tips; cells past 5 m up 8.6x
(4,948 -> 42,385) while the fine rills are retained. Verified descending, not
contour-locked: 0/155 components have drop/extent < 0.12 (median 1.13).

EROS body version -> 2 (deposit cap inserted after the carve cap); v1 payloads
are skipped whole by the existing rule. HydraulicErosion.VERSION now reads
BlueprintFormat.EROS_VERSION instead of restating it — the local copy had
already drifted and stamped a v2 body as v1, which readers decode with every
float shifted by one field.

Oracle green on both seeds (1280587109, 1512575962): 1_biomes/0_water
md5-identical erosion-ON vs OFF, BIOM/WBID bitwise equal. Flood guard 0 new
water px, 0 below-sea cells touched, crater zone untouched, island top
unchanged, carve field isotropic to 1.4% across the folded 45deg period.
Erosion pass 34 s at these dials.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
This commit is contained in:
Stewart Howe 2026-08-10 04:16:33 -04:00
parent 56ac17e670
commit cc6a24d2b9
8 changed files with 105 additions and 59 deletions
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4
Tools/Scripts/RoundTripHarness.cs
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@ -258,9 +258,9 @@ public partial class RoundTripHarness : Node
bool same = ea.Version == eb.Version
&& ea.DropletCount == eb.DropletCount && ea.Lifetime == eb.Lifetime
&& ea.BrushRadius == eb.BrushRadius && ea.SeedOffset == eb.SeedOffset;
float[] fa = { ea.CarveCapM, ea.SeaMarginM, ea.Inertia, ea.CapacityFactor, ea.MinSlopeM,
float[] fa = { ea.CarveCapM, ea.DepositCapM, ea.SeaMarginM, ea.Inertia, ea.CapacityFactor, ea.MinSlopeM,
ea.ErodeRate, ea.DepositRate, ea.Evaporation, ea.Gravity, ea.CraterExclFactor };
float[] fb = { eb.CarveCapM, eb.SeaMarginM, eb.Inertia, eb.CapacityFactor, eb.MinSlopeM,
float[] fb = { eb.CarveCapM, eb.DepositCapM, eb.SeaMarginM, eb.Inertia, eb.CapacityFactor, eb.MinSlopeM,
eb.ErodeRate, eb.DepositRate, eb.Evaporation, eb.Gravity, eb.CraterExclFactor };
for (int i = 0; i < fa.Length; i++)
if (System.BitConverter.SingleToInt32Bits(fa[i]) != System.BitConverter.SingleToInt32Bits(fb[i])) same = false;