Create src/multiplayer/startGrid.js

src/multiplayer/startGrid.js

@@ -0,0 +1,75 @@
+import * as THREE from 'three';
+
+export const START_GRID_Y = 0.28;
+export const START_GRID_LATERAL_OFFSET = 2.35;
+export const START_GRID_ROW_SPACING = 6.0;
+export const START_GRID_INITIAL_OFFSET = 8.0;
+export const MULTIPLAYER_COUNTDOWN_MS = 3600;
+export const START_SYNC_GRACE_MS = 5000;
+export const START_SYNC_ANCHOR_TOLERANCE = 24;
+export const CENTER_FALLBACK_RADIUS = 18;
+
+const TRACK_POINTS = [
+  new THREE.Vector3(0, 0, 100),
+  new THREE.Vector3(50, 0, 90),
+  new THREE.Vector3(80, 0, 60),
+  new THREE.Vector3(120, 0, 40),
+  new THREE.Vector3(120, 0, -20),
+  new THREE.Vector3(105, 0, -50),
+  new THREE.Vector3(120, 0, -80),
+  new THREE.Vector3(120, 0, -140),
+  new THREE.Vector3(70, 0, -140),
+  new THREE.Vector3(70, 0, -70),
+  new THREE.Vector3(10, 0, -70),
+  new THREE.Vector3(10, 0, -140),
+  new THREE.Vector3(-40, 0, -140),
+  new THREE.Vector3(-80, 0, -120),
+  new THREE.Vector3(-140, 0, -80),
+  new THREE.Vector3(-150, 0, -20),
+  new THREE.Vector3(-110, 0, 30),
+  new THREE.Vector3(-140, 0, 70),
+  new THREE.Vector3(-90, 0, 110),
+  new THREE.Vector3(-40, 0, 100),
+];
+
+const SHARED_CURVE = new THREE.CatmullRomCurve3(TRACK_POINTS, true, 'centripetal', 0.5);
+const SHARED_TRACK_LENGTH = SHARED_CURVE.getLength();
+const UP = new THREE.Vector3(0, 1, 0);
+
+function normalizeSlotIndex(slotIndex = 0) {
+  if (!Number.isFinite(slotIndex)) return 0;
+  return Math.max(0, Math.floor(slotIndex));
+}
+
+export function getStartTransformForSlot(slotIndex = 0) {
+  const normalizedSlot = normalizeSlotIndex(slotIndex);
+  const row = Math.floor(normalizedSlot / 2);
+  const side = normalizedSlot % 2 === 0 ? -1 : 1;
+  const baseT = (1 - ((row * START_GRID_ROW_SPACING + START_GRID_INITIAL_OFFSET) / SHARED_TRACK_LENGTH) + 1) % 1;
+  const point = SHARED_CURVE.getPointAt(baseT);
+  const tangent = SHARED_CURVE.getTangentAt(baseT).normalize();
+  const lateral = new THREE.Vector3().crossVectors(UP, tangent).normalize();
+  const heading = Math.atan2(tangent.x, tangent.z);
+  const position = point.clone().addScaledVector(lateral, side * START_GRID_LATERAL_OFFSET).setY(START_GRID_Y);
+  return {
+    slotIndex: normalizedSlot,
+    progress: baseT,
+    heading,
+    position: { x: position.x, y: position.y, z: position.z },
+  };
+}
+
+export function isNearCenterPosition(position, radius = CENTER_FALLBACK_RADIUS) {
+  if (!position) return true;
+  const x = Number(position.x ?? 0);
+  const z = Number(position.z ?? 0);
+  return Number.isFinite(x) && Number.isFinite(z) ? Math.hypot(x, z) <= radius : true;
+}
+
+export function distanceBetweenPositions(a, b) {
+  if (!a || !b) return Number.POSITIVE_INFINITY;
+  const dx = Number(a.x ?? 0) - Number(b.x ?? 0);
+  const dy = Number(a.y ?? 0) - Number(b.y ?? 0);
+  const dz = Number(a.z ?? 0) - Number(b.z ?? 0);
+  return Math.hypot(dx, dy, dz);
+}