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feat: submarine coast shelf + elongation dials (terrain-water task 11)

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COAST. The task's premise -- "the island edge is the steepest part" -- is
right, and the diagnostic locates it precisely: it is the SEABED, not the
land. HeightCurve.Apply returns early at and below sea level, so tasks
05-09 reshaped the land and never touched the water. Measured on the same
seed, distance-from-shore vs height:

                       land reaches 10 m   seabed reaches 10 m   gradient
  curve OFF                   31 px               31 px       0.254/0.258
  curve ON (ships)           186 px               31 px       0.038/0.258

So the landward side is ALREADY the broad shallow shelf terrain_design.md
asks for -- 54% of the island sits under 14 m -- and flattening it further
would only make it mushy. What is left is a shoreline that shelves gently
on land and then drops 6.7x steeper the moment it goes under.

CoastShelf fixes that side: depth' = depth * (1 - 0.775*exp(-depth/100 m)).
The seabed leaves the waterline at 22.5% of its former gradient and
recovers smoothly, so deep water and the Trench keep their shape. Measured
after: 5 m depth at 43 px (was 15), 10 m at 75 (was 31), 30 m at 150 (was
94) -- a 2.4-2.9x wider shallows.

It is strictly positive for positive depth, so it CANNOT move the waterline
by one pixel. Biomes and water bodies come out bit-identical, which is why
the coast is separable from elongation in the batch rather than tangled
with it -- contrary to the task's expectation that all coast work moves
biomes.

ELONGATION. IslandAxisX/Y replace the 1.15/0.90 literals (the spine shares
AxisX, as it always shared the literal). Sized by replaying candidate
falloffs against real terrain rather than guessing -- the replay reproduces
the shipped extents exactly, bbox and land count.

That replay says the task's suggested 1.30/0.85 buys +2.0% aspect, because
THE ISLAND IS ALREADY TRENCH-CLAMPED IN X: it spans 90.5% of the map width,
and 1.15 -> 1.40 moves the west coast only 393 -> ~360 px. Aspect responds
almost entirely to AxisY, which costs land:

  1.30/0.85  +2.0% aspect  +2.9% land      1.30/0.80  +4.9%  -2.2%
  1.30/0.82  +3.7% aspect  -0.1% land      1.30/0.75 +11.5%  -7.3%

Default 1.30/0.78 -- a visible step (+~8% aspect, measured 1.137 -> 1.200)
at ~4% land. The developer's eye tunes it from the batch; the table above
is the price list.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
This commit is contained in:
Stewart Howe 2026-08-08 23:29:49 -04:00
parent 896a428d47
commit 566abe9784
3 changed files with 105 additions and 9 deletions
Download patch file Download diff file Expand all files Collapse all files

42
Core/Scripts/ConfigManager.cs
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@ -44,6 +44,27 @@ namespace IslaApocalypse.Core // Change this if your namespace is different
public static float ShelfReliefAmp = 3.0f;
public static float ShelfEdgeVariation = 12.0f;
// Island falloff shaping (task 11).
//
// CoastProfile: "wide" adds the submarine shelf. The height curve is identity
// at and below sea, so it never reached the seabed — measured, land rises from
// the shoreline at 0.038 m/px while the seabed drops at 0.258 m/px. "steep" is
// the pre-task-11 seabed, kept for A/B. The shelf cannot move the waterline, so
// biomes and water are bit-identical either way. Default: wide.
//
// IslandAxisX/Y: the falloff axis ratios (pre-task-11: 1.15 / 0.90). NOTE,
// measured: the island is already Trench-clamped in x at ~90% of the map width,
// so AxisX is a weak lever — aspect responds almost entirely to AxisY, which
// trades against land area. These MOVE THE COASTLINE, so they move biomes by
// design; elongated seeds have a new biome baseline.
public static string CoastProfile = "wide";
public static float IslandAxisX = 1.30f;
public static float IslandAxisY = 0.78f;
// The pre-task-11 axis ratios, so legacy/steep runs can restore them exactly.
public const float LEGACY_AXIS_X = 1.15f;
public const float LEGACY_AXIS_Y = 0.90f;
public static void LoadConfig()
{
string path = "res://ServerConfig.json";
@ -147,6 +168,27 @@ namespace IslaApocalypse.Core // Change this if your namespace is different
ShelfEdgeVariation = (float)data["ShelfEdgeVariation"];
}
// Extract the island-falloff dials (task 11)
if (data.ContainsKey("CoastProfile"))
{
string coast = (string)data["CoastProfile"];
if (coast == "steep" || coast == "wide")
CoastProfile = coast;
else
GD.PrintErr($"[ConfigManager] Unknown CoastProfile '{coast}'. Keeping '{CoastProfile}'.");
}
if (data.ContainsKey("IslandAxisX")) IslandAxisX = (float)data["IslandAxisX"];
if (data.ContainsKey("IslandAxisY")) IslandAxisY = (float)data["IslandAxisY"];
// The axis ratios divide map extents; a zero or negative one is a divide-by-
// zero that would silently produce an all-ocean map. Refuse it loudly.
if (IslandAxisX <= 0.01f || IslandAxisY <= 0.01f)
{
GD.PrintErr($"[ConfigManager] IslandAxisX/Y must be > 0.01 (got {IslandAxisX}/{IslandAxisY}). Restoring legacy {LEGACY_AXIS_X}/{LEGACY_AXIS_Y}.");
IslandAxisX = LEGACY_AXIS_X;
IslandAxisY = LEGACY_AXIS_Y;
}
switch (profile)
{
case "4K":