PROCITY/web/js/world/ground.js

// PROCITY Lane B — ground.js
// Roads, footpaths, kerbs, the market plaza, and a base ground plane, built ONCE as merged strips
// per material (not per-chunk streamed). Rationale: the street graph is a handful of edges; merged
// flat quads are a few draw calls total and — unlike per-chunk road clipping — can never seam.
// UV tiling is baked into the geometry so one shared ground material serves strips of any length.
// (If Lane A ships a many-hundred-edge city, Lane F revisits streaming the ground.)

import * as THREE from 'three';
import { mergeGeometries } from 'three/addons/utils/BufferGeometryUtils.js';
import { resolveEdges } from './planutil.js';

const FOOT = 3.5;        // footpath width
const TILE = 5;          // metres per texture tile
const OVERLAP = 1.5;     // road segments overrun their nodes so intersections fill

// Horizontal quad in XZ centred at (cx,cz), aligned to unit dir/perp, size len×wid, at height y.
// UVs baked to tile every TILE metres.
function hQuad(cx, cz, dir, perp, len, wid, y) {
  const hl = len / 2, hw = wid / 2;
  const ax = dir.x * hl, az = dir.z * hl;   // along
  const bx = perp.x * hw, bz = perp.z * hw;  // across
  const P = (sa, sb) => [cx + sa * ax + sb * bx, y, cz + sa * az + sb * bz];
  const c0 = P(-1, -1), c1 = P(1, -1), c2 = P(1, 1), c3 = P(-1, 1);
  const repU = Math.max(1, len / TILE), repV = Math.max(1, wid / TILE);
  const g = new THREE.BufferGeometry();
  // winding c0,c2,c1 / c0,c3,c2 so the geometric normal points +Y (up) — FrontSide stays visible.
  g.setAttribute('position', new THREE.BufferAttribute(new Float32Array([
    ...c0, ...c2, ...c1, ...c0, ...c3, ...c2]), 3));
  g.setAttribute('uv', new THREE.BufferAttribute(new Float32Array([
    0, 0, repU, repV, repU, 0, 0, 0, 0, repV, repU, repV]), 2));
  g.setAttribute('normal', new THREE.BufferAttribute(new Float32Array([
    0, 1, 0, 0, 1, 0, 0, 1, 0, 0, 1, 0, 0, 1, 0, 0, 1, 0]), 3));
  return g;
}

// Axis-aligned rectangle helper (plaza, base plane).
function rectGeo(cx, cz, w, d, y, tile = TILE) {
  return hQuad(cx, cz, new THREE.Vector3(1, 0, 0), new THREE.Vector3(0, 0, 1), w, d, y);
}

export function buildGround(plan, skins) {
  const group = new THREE.Group();
  group.name = 'ground';
  const edges = resolveEdges(plan);

  const roadGeos = [], footGeos = [], kerbGeos = [];
  const dir = new THREE.Vector3(), perp = new THREE.Vector3();

  for (const e of edges) {
    const dx = e.bx - e.ax, dz = e.bz - e.az;
    const len = Math.hypot(dx, dz) || 1;
    dir.set(dx / len, 0, dz / len);
    perp.set(-dir.z, 0, dir.x);
    const cx = (e.ax + e.bx) / 2, cz = (e.az + e.bz) / 2;
    const roadLen = len + OVERLAP * 2;
    roadGeos.push(hQuad(cx, cz, dir, perp, roadLen, e.width, 0.0));
    // footpaths flank the road
    const off = e.width / 2 + FOOT / 2;
    footGeos.push(hQuad(cx + perp.x * off, cz + perp.z * off, dir, perp, roadLen, FOOT, 0.02));
    footGeos.push(hQuad(cx - perp.x * off, cz - perp.z * off, dir, perp, roadLen, FOOT, 0.02));
    // low kerbs between road and footpath
    const koff = e.width / 2 + 0.12;
    kerbGeos.push(hQuad(cx + perp.x * koff, cz + perp.z * koff, dir, perp, roadLen, 0.24, 0.06));
    kerbGeos.push(hQuad(cx - perp.x * koff, cz - perp.z * koff, dir, perp, roadLen, 0.24, 0.06));
  }

  // market plaza (brickpave) over the central square
  const sq = (plan.districts || []).find((d) => d.kind === 'market');
  const plazaGeos = [];
  if (sq) plazaGeos.push(rectGeo(0, 0, 46, 46, 0.015));

  // base ground plane under the whole town (grass/dirt), sized to the plan extent
  let minX = -60, maxX = 60, minZ = -60, maxZ = 60;
  for (const n of plan.streets.nodes) { minX = Math.min(minX, n.x); maxX = Math.max(maxX, n.x); minZ = Math.min(minZ, n.z); maxZ = Math.max(maxZ, n.z); }
  for (const l of plan.lots) { minX = Math.min(minX, l.x); maxX = Math.max(maxX, l.x); minZ = Math.min(minZ, l.z); maxZ = Math.max(maxZ, l.z); }
  const bw = (maxX - minX) + 120, bd = (maxZ - minZ) + 120;
  const bcx = (minX + maxX) / 2, bcz = (minZ + maxZ) / 2;
  const baseGeo = rectGeo(bcx, bcz, bw, bd, -0.03);

  const meshes = [];
  const add = (geos, material, receive = true) => {
    if (!geos.length) return;
    const merged = mergeGeometries(geos, false);
    geos.forEach((g) => g.dispose());
    const m = new THREE.Mesh(merged, material);
    m.receiveShadow = receive; m.castShadow = false;
    group.add(m); meshes.push(m);
  };

  const roadSkin = 'djsim-road', footSkin = 'djsim-footpath', grassSkin = 'grass', plazaSkin = 'brickpave';
  add([baseGeo], skins.groundMat(grassSkin));
  add(roadGeos, skins.groundMat(roadSkin));
  add(footGeos, skins.groundMat(footSkin));
  add(plazaGeos, skins.groundMat(plazaSkin));
  const kerbMat = new THREE.MeshStandardMaterial({ color: 0x9a948c, roughness: 0.9 });
  add(kerbGeos, kerbMat);

  function dispose() {
    for (const m of meshes) m.geometry.dispose();
    kerbMat.dispose();
    group.clear();
  }
  return { group, dispose };
}