life.js

// Inhabitants. What separates a world model from scenery is that something lives
// in it and the terrain is the reason it lives where it does.
//
// Animals are spawned through the habitat rules in hydro.js, so their range comes
// out of the same water and slope fields that shaped the vegetation. Once placed
// they act on two drives — thirst and hunger — and the map answers both: water
// where the drainage put it, forage where the moisture allowed it. Nobody is
// scripted to walk to a particular spot.

import { GRID, WORLD } from './world.js';
import { HABITAT, populate } from './hydro.js';

export const SPECIES = [
    { id: 'grazer',   label: 'Grazing herd', habitat: 'plain',     weight: 30, scale: 1.0,
      herd: 7, speed: 2.4, color: '#b6a074', drinks: true,  eats: 'plant' },
    { id: 'browser',  label: 'Forest browser', habitat: 'forest',  weight: 18, scale: 1.3,
      herd: 3, speed: 1.8, color: '#8d7a52', drinks: true,  eats: 'plant' },
    { id: 'predator', label: 'Predator',     habitat: 'plain',     weight: 5,  scale: 1.15,
      herd: 2, speed: 3.4, color: '#8a5b46', drinks: true,  eats: 'meat' },
    { id: 'wader',    label: 'Wader',        habitat: 'riverbank', weight: 12, scale: 0.55,
      herd: 5, speed: 1.6, color: '#d8d2c4', drinks: false, eats: 'fish' },
    { id: 'fish',     label: 'Fish',         habitat: 'water',     weight: 16, scale: 0.5,
      herd: 9, speed: 2.0, color: '#6f9fb5', drinks: false, eats: 'plant', aquatic: true },
    { id: 'flyer',    label: 'Cliff flyer',  habitat: 'cliff',     weight: 8,  scale: 0.7,
      herd: 3, speed: 5.0, color: '#9a9a8c', drinks: false, eats: 'meat', flying: true },
    { id: 'climber',  label: 'Highland herd', habitat: 'highland', weight: 11, scale: 0.9,
      herd: 4, speed: 2.0, color: '#a8a091', drinks: true,  eats: 'plant' },
];

const idx = (x, y) => y * GRID + x;

/** Sample the world at a world-space point; the shared lookup for every drive. */
export function probe(world, x, z) {
    const step = WORLD / (GRID - 1);
    const gx = Math.min(GRID - 1, Math.max(0, Math.round((x + WORLD / 2) / step)));
    const gy = Math.min(GRID - 1, Math.max(0, Math.round((z + WORLD / 2) / step)));
    const i = idx(gx, gy);
    const dx = world.height[idx(Math.min(GRID - 1, gx + 1), gy)] - world.height[idx(Math.max(0, gx - 1), gy)];
    const dy = world.height[idx(gx, Math.min(GRID - 1, gy + 1))] - world.height[idx(gx, Math.max(0, gy - 1))];
    return {
        gx, gy, i,
        height: world.height[i],
        slope: Math.hypot(dx, dy) / (step * 2),
        moisture: world.moisture[i],
        waterDepth: world.water.depth[i],
        waterSurface: world.water.surface[i],
        region: world.regions[world.owner[i]],
    };
}

/** Does this species tolerate standing here? Same predicate that placed it. */
function habitable(sp, p) {
    const rule = HABITAT[sp.habitat] || HABITAT.plain;
    return p.waterDepth >= rule.water[0] && p.waterDepth <= rule.water[1] &&
           p.slope >= rule.slope[0] && p.slope <= rule.slope[1] &&
           p.height >= rule.height[0] && p.height <= rule.height[1] &&
           p.moisture >= rule.moist[0] && p.moisture <= rule.moist[1];
}

/**
 * Spawn the cast and give each individual its own drives. Herd members keep a
 * home point so a herd stays a herd instead of dissolving into a random walk.
 */
export function spawn(world, rng, budget = 150) {
    const raw = populate(world, SPECIES, rng, { worldSize: WORLD, budget });
    const byId = new Map(SPECIES.map(s => [s.id, s]));
    return raw.map(a => {
        const sp = byId.get(a.id);
        return {
            ...a, sp,
            vx: 0, vz: 0,
            homeX: a.x, homeZ: a.z,
            thirst: rng() * 0.6,
            phase: rng() * Math.PI * 2,
            wanderT: rng() * 4,
            targetX: a.x, targetZ: a.z,
        };
    });
}

/**
 * One tick. Thirsty animals that drink head for the nearest water they can find;
 * everyone else drifts around their home range. Movement is refused where the
 * habitat test fails, which is what keeps grazers off cliffs and fish in rivers
 * without a single hand-placed boundary.
 */
export function step(world, agents, dt, waterPoints) {
    const half = WORLD / 2 - 3;
    for (const a of agents) {
        const sp = a.sp;
        a.thirst = Math.min(1.6, a.thirst + dt * 0.045);
        a.wanderT -= dt;

        if (sp.drinks && a.thirst > 1 && waterPoints.length) {
            // nearest water: the drainage decided where that is
            let best = null, bestD = Infinity;
            for (const w of waterPoints) {
                const d = (w.x - a.x) ** 2 + (w.z - a.z) ** 2;
                if (d < bestD) { bestD = d; best = w; }
            }
            if (best) {
                a.targetX = best.x; a.targetZ = best.z;
                if (bestD < 9) { a.thirst = 0; a.wanderT = 0; }
            }
        } else if (a.wanderT <= 0) {
            const r = sp.herd ? 9 : 16;
            a.targetX = a.homeX + (Math.random() - 0.5) * r * 2;
            a.targetZ = a.homeZ + (Math.random() - 0.5) * r * 2;
            a.wanderT = 3 + Math.random() * 5;
        }

        const dx = a.targetX - a.x, dz = a.targetZ - a.z;
        const dist = Math.hypot(dx, dz) || 1;
        const speed = sp.speed * (a.thirst > 1 ? 1.35 : 1);
        const nx = a.x + (dx / dist) * speed * dt;
        const nz = a.z + (dz / dist) * speed * dt;

        const p = probe(world, nx, nz);
        if (Math.abs(nx) < half && Math.abs(nz) < half && (sp.flying || habitable(sp, p))) {
            a.x = nx; a.z = nz;
            a.rot = Math.atan2(dx, dz);
            a.y = sp.aquatic ? p.waterSurface - 0.35 - Math.sin(a.phase) * 0.15
                : sp.flying ? p.height + 6 + Math.sin(a.phase * 0.7) * 1.5
                : Math.max(p.height, p.waterDepth > 0 ? p.waterSurface : p.height);
        } else {
            a.wanderT = 0;                   // blocked: pick somewhere else next tick
        }
        a.phase += dt * (sp.flying ? 2.2 : 3.2);
    }
}

/**
 * A body in a few parts. One squashed ellipsoid reads as a pebble from any
 * distance — it is the legs holding it off the ground and the head sticking out
 * in front that make the eye call it an animal, and both are cheap because every
 * part is one more instanced mesh sharing the same transforms.
 */
export function bodyParts(THREE, sp) {
    if (sp.flying) {
        const wings = new THREE.ConeGeometry(0.62, 1.9, 4);
        wings.rotateX(Math.PI / 2);
        return [{ geo: wings, color: sp.color }];
    }
    if (sp.aquatic) {
        const body = new THREE.ConeGeometry(0.3, 1.4, 5);
        body.rotateX(-Math.PI / 2);
        const tail = new THREE.ConeGeometry(0.26, 0.5, 4);
        tail.rotateX(Math.PI / 2);
        tail.translate(0, 0, 0.85);
        return [{ geo: body, color: sp.color }, { geo: tail, color: sp.color }];
    }

    const body = new THREE.SphereGeometry(0.55, 8, 6);
    body.scale(0.78, 0.74, 1.35);
    body.translate(0, 0.95, 0);

    const head = new THREE.SphereGeometry(0.27, 7, 5);
    head.scale(0.9, 0.9, 1.2);
    head.translate(0, 1.24, 0.82);

    // one block for all four legs: at this size separate cylinders are invisible
    // detail, but the gap under the body is what sells the silhouette
    const legs = new THREE.BoxGeometry(0.62, 0.62, 0.9);
    legs.translate(0, 0.33, 0);

    const dark = '#4a3a2c';
    return [
        { geo: body, color: sp.color },
        { geo: head, color: sp.color },
        { geo: legs, color: dark },
    ];
}

/** Where drinking animals can reach water — sampled once per world, not per tick. */
export function waterAccess(world, limit = 260) {
    const pts = [];
    const step = WORLD / (GRID - 1);
    for (let y = 1; y < GRID - 1; y += 2) {
        for (let x = 1; x < GRID - 1; x += 2) {
            const i = idx(x, y);
            if (world.water.depth[i] < 0.05) continue;
            // only the shoreline is drinkable; the middle of a lake is not a place
            // a land animal can stand
            const edge = [idx(x + 1, y), idx(x - 1, y), idx(x, y + 1), idx(x, y - 1)]
                .some(j => world.water.depth[j] < 0.02);
            if (!edge) continue;
            pts.push({ x: -WORLD / 2 + x * step, z: -WORLD / 2 + y * step });
            if (pts.length >= limit) return pts;
        }
    }
    return pts;
}