Core/Scripts/DrainageAnalysis.cs is the reference's DrainageAnalysis ported verbatim: the
Barnes priority-flood routing fill (8-connected, seeded from the four borders, index
tiebreak, pit fills ONE ULP above the parent so every filled cell keeps a strictly
descending path to its spill; the terrain heightmap itself is never written - the fill lives
in its own array), terminal-basin qualification (depth >= 2 m AND area >= 10,000 px; the rest
are pits filled through), D8 flow directions on the routing surface - FOR ANALYSIS ONLY, the
reverted-as-carving landmine stated in the file - Kahn accumulation, the memoised destination
walk crediting a terminal basin with TOTAL inflow, sea-reaching outlets ranked by drainage
area with the outlet separation, main stems by max accumulation, mountain exits from the
along-stem grade, lean tributaries, lean endorheic terminals, and the promoted giants
(provisional routes computed as the reference did, not drawn - routing is a later task).
WorldScale-denominated; Dir / Acc / Filled / FullFilled / BasinId / BasinInflow exposed so the
caller can prove the invariants.
"The sea" is the OCEAN body from the region layer: RegionLabeling.OceanMask - the 4-connected
water component touching the border, on the CLASSIFY field (the water-side complement of the
land contract). Enclosed lagoons, lake beds and island-fringe pockets are ordinary terrain to
the router.
DrainageTool (4 task-11 seeds at 8192, the eroded fields bit-identical to the 11 dumps)
renders the log-scaled accumulation map and the promoted-candidates overlay (trunks cyan,
endorheic giants orange, lean terminals red; nothing carved) and writes the accumulation
.f32. Oracle, all passing: render AND classify fields bit-identical before/after the analysis
(zero terrain cells written), no water added, full fill >= original everywhere with a
non-ascending path to the border from every cell, ocean mask all below sea and on the border,
dir/acc/candidates identical across two runs.
Endorheic basins are the expected first-class output: on every seed the top giants out-drain
the top trunks - the biggest drainages pool inland because erosion delivers the upland network
only and cannot cross the flats.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013EY3ZTF6NwzF8ukBHQXSK7
Core/Scripts/RegionLabeling.cs is the shared-infra contract, built to the letter: it runs on
the CLASSIFY (raw) field; land is 8-connected, the deliberate complement of water's 4 (a
diagonal isthmus joins; the water either side stays separate); a component is a maximal
8-connected set of land cells; the MAINLAND is the component containing the map centre —
not merely the largest, which a later fragmentation step could flip — with a flagged
fallback to the largest if the centre were ever water (asserted, never needed: oracle m);
every other component is an island; per component id / sizeCells / centroid / hemisphere
(by centroid, one label per island) / isMainland. Ids come from a fixed scan order and are
proven stable across two generations (oracle o, 16.8M cells). It knows nothing about
offshore or stamped. Engine-free, in Core as C++-candidate math; the hemisphere convention
moved there with it, OffshoreAnalysis aliases it.
Tools/Scripts/RegionPass.cs is pass 1c: label, revert, relabel, tag. The island tag
(renamed IsIsland; IslandHemisphere from the component's centroid; Pass1Result.Regions
carries the whole table) is now a CONSEQUENCE of labeling — every non-mainland component.
That is the fix for the chat2/06 overlay, which tagged only what the offshore pass raised:
1063685222 has 11 natural islands including a 94,511-cell detached mass, 20260821 has 19,
all grey in 06's tags.png and all coloured now. The offshore pass itself is untouched; its
internal Tag stays for its own guards and is no longer exported.
The speck revert (TerrainGenConfig.SpeckRevert / MinLandComponentFrac) lowers every
non-mainland component below the threshold to the mean of its ring of adjacent sea cells,
held strictly below sea. Origin-blind: a natural nub goes the same way as an offshore dot
(6 natural components / 273 cells on the bare 1063685222 field at threshold_mid — reported
as a3r, informational). Lower-only and component-only are asserted cell by cell in the
pass and re-proven on the finished fields by oracle n (mainland bit-identical filter OFF
vs ON; every changed cell in a sub-threshold island, lowered below sea); the mainland is
never a candidate and its size is asserted unchanged across the revert. A reverted
offshore island leaves its submerged skirt as a shoal — not this component, by the rule.
Classify/render consistency is by construction (pass 1, curve identity at sea) and
asserted by oracle k. Deliberately OFF in the bare TerrainGenConfig for the reason the
shelf and islets are: the raw field has natural specks, so default-ON would move the
calibration pool and every regression dump; the batch turns it on.
Thresholds swept on 8 seeds at 4096 (1e-5 / 3e-5 / 1e-4 of the map = 168 / 503 / 1,678
cells): low removes 0–6 nubs per seed, mid (the config default, equal to the offshore
guard) 2–11, high 26–36 — most of the offshore islands, the "fewer, bigger" bookend. The
count/size table carries natural / pre / post counts per hemisphere, min/median/mean/max
and a log-spaced size histogram — the instrument for the southern-stretch step.
Oracle, all passing: a1, a3, a4 (8192, 67M cells) with labeling ON + revert OFF; a6 NEW —
labeling ON + revert OFF on the 06 preset bit-identical to the 06 batch's render field
(labeling is pure analysis); j0; m, n, o, i, j, k, l, b per field. Batch:
BatchRoot(7, "region_labeling") — exactly 4 plates (three thresholds on 1063685222,
threshold_mid on 20260821, the table's most-natural-islands seed), each with grayscale /
.f32 / relief / the labeled-regions overlay / the tag overlay, plus count_size_table.md/.csv.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013EY3ZTF6NwzF8ukBHQXSK7
