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* Deterministic scatter helpers for the seabed decorations.
*
* The seabed itself is a subdivided, gently displaced plane built
* directly in the renderer component. This module generates the
* positions + per-instance parameters for:
* - rocks (grey chunks)
* - seagrass clusters (tufts of tall thin blades that sway)
* - corals / sea flowers (coloured tufts)
*
* All layouts are seeded so the ocean floor is reproducible.
*/
import { SEABED_RADIUS, MAIN_ISLAND_RADIUS } from "./sceneConstants";
function mulberry32(seed: number): () => number {
let state = seed >>> 0;
return () => {
state = (state + 0x6d2b79f5) >>> 0;
let t = state;
t = Math.imul(t ^ (t >>> 15), t | 1);
t ^= t + Math.imul(t ^ (t >>> 7), t | 61);
return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
};
}
/** Rocks: scattered chunks of grey stone. */
export interface RockPlacement {
position: [number, number]; // XZ, y comes from the seabed height at that point
scale: [number, number, number];
rotationY: number;
/** 0-based index into a small grey palette. */
shadeIndex: number;
}
/** Seagrass: a cluster of 3-5 tall thin blades at one location. */
export interface SeagrassCluster {
position: [number, number];
/** Per-blade offsets (relative to cluster centre) + height. */
blades: Array<{ offset: [number, number]; height: number; phase: number }>;
colorIndex: number;
}
/** Coral / sea flower tuft. */
export interface CoralPlacement {
position: [number, number];
scale: number;
colorIndex: number;
/** 0: cone, 1: icosahedron, 2: sphere cluster. */
shape: 0 | 1 | 2;
}
export interface SeabedLayout {
rocks: RockPlacement[];
seagrass: SeagrassCluster[];
corals: CoralPlacement[];
}
export const ROCK_SHADES: readonly string[] = Object.freeze([
"#6e6a66",
"#7a7470",
"#8a8581",
"#5e5a55"
]);
export const SEAGRASS_COLORS: readonly string[] = Object.freeze([
"#2f6a3a",
"#4a8f4a",
"#3a7d4e",
"#5ca55f"
]);
export const CORAL_COLORS: readonly string[] = Object.freeze([
"#ff7f7f",
"#ffbdbd",
"#ff99cc",
"#a65fd6",
"#ffe066",
"#ff6ba3"
]);
export const SEABED_SEED = 0x5ea7bed0;
export const DEFAULT_ROCK_COUNT = 60;
export const DEFAULT_SEAGRASS_COUNT = 45;
export const DEFAULT_CORAL_COUNT = 30;
/** Inner scatter radius - stay clear of the main island's underwater footprint. */
export const SEABED_INNER_RADIUS = MAIN_ISLAND_RADIUS + 2;
/**
* Height of the seabed surface at position (x, z), relative to the
* plane's own y=0. The seabed mesh sits at `SEABED_Y`, and vertices are
* displaced by this function to give gentle dunes. Pure function so
* it's reusable from the renderer (for placing rocks on the surface)
* and from unit tests.
*/
export function seabedHeightAt(x: number, z: number): number {
// Sum of two cheap sinusoids + a low-frequency radial mound so the
// floor is not completely flat near the centre.
const a = Math.sin(x * 0.12) * 0.8;
const b = Math.cos(z * 0.15) * 0.7;
const c = Math.sin((x + z) * 0.07) * 0.5;
const r = Math.sqrt(x * x + z * z);
const mound = Math.cos(r * 0.04) * 0.6;
return a + b + c + mound;
}
/** Sample a point uniformly in the seabed annulus. */
function sampleSeabedPoint(rand: () => number): [number, number] {
const innerSq = SEABED_INNER_RADIUS * SEABED_INNER_RADIUS;
const outerSq = SEABED_RADIUS * SEABED_RADIUS;
const u = rand();
const r = Math.sqrt(u * (outerSq - innerSq) + innerSq);
const theta = rand() * Math.PI * 2;
return [Math.cos(theta) * r, Math.sin(theta) * r];
}
export function generateSeabedLayout(
rockCount: number = DEFAULT_ROCK_COUNT,
seagrassCount: number = DEFAULT_SEAGRASS_COUNT,
coralCount: number = DEFAULT_CORAL_COUNT,
seed: number = SEABED_SEED
): SeabedLayout {
const rand = mulberry32(seed);
const rocks: RockPlacement[] = [];
for (let i = 0; i < rockCount; i++) {
const [x, z] = sampleSeabedPoint(rand);
const baseScale = 0.4 + rand() * 1.1;
rocks.push({
position: [x, z],
scale: [
baseScale * (0.8 + rand() * 0.4),
baseScale * (0.6 + rand() * 0.3),
baseScale * (0.8 + rand() * 0.4)
],
rotationY: rand() * Math.PI * 2,
shadeIndex: Math.floor(rand() * ROCK_SHADES.length)
});
}
const seagrass: SeagrassCluster[] = [];
for (let i = 0; i < seagrassCount; i++) {
const [x, z] = sampleSeabedPoint(rand);
const bladeCount = 3 + Math.floor(rand() * 3); // [3,5]
const blades = [];
for (let b = 0; b < bladeCount; b++) {
blades.push({
offset: [(rand() - 0.5) * 0.4, (rand() - 0.5) * 0.4] as [number, number],
height: 0.9 + rand() * 0.8,
phase: rand() * Math.PI * 2
});
}
seagrass.push({
position: [x, z],
blades,
colorIndex: Math.floor(rand() * SEAGRASS_COLORS.length)
});
}
const corals: CoralPlacement[] = [];
for (let i = 0; i < coralCount; i++) {
const [x, z] = sampleSeabedPoint(rand);
corals.push({
position: [x, z],
scale: 0.35 + rand() * 0.5,
colorIndex: Math.floor(rand() * CORAL_COLORS.length),
shape: Math.floor(rand() * 3) as 0 | 1 | 2
});
}
return { rocks, seagrass, corals };
}
export const SEABED_LAYOUT: Readonly<SeabedLayout> = Object.freeze(generateSeabedLayout());
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