perf(map): snap assets to terrain

src/hooks/three/useTerrainHeight.ts

@@ -0,0 +1,64 @@
+import { useMemo } from "react";
+import { useGLTF } from "@react-three/drei";
+import * as THREE from "three";
+import type { Vector3Tuple } from "@/types/three/three";
+
+const TERRAIN_MODEL_PATH = "/models/terrain/model.gltf";
+const RAYCAST_Y = 500;
+const RAYCAST_FAR = 1000;
+const DOWN = new THREE.Vector3(0, -1, 0);
+
+interface TerrainHeightSampler {
+  getHeight: (x: number, z: number) => number | null;
+}
+
+function createTerrainHeightSampler(
+  scene: THREE.Object3D,
+): TerrainHeightSampler {
+  const meshes: THREE.Mesh[] = [];
+  const raycaster = new THREE.Raycaster(
+    new THREE.Vector3(),
+    DOWN,
+    0,
+    RAYCAST_FAR,
+  );
+
+  scene.updateMatrixWorld(true);
+  scene.traverse((child) => {
+    if (child instanceof THREE.Mesh) {
+      meshes.push(child);
+    }
+  });
+
+  return {
+    getHeight: (x, z) => {
+      raycaster.set(new THREE.Vector3(x, RAYCAST_Y, z), DOWN);
+      const hit = raycaster.intersectObjects(meshes, false)[0];
+      return hit?.point.y ?? null;
+    },
+  };
+}
+
+export function useTerrainHeightSampler(): TerrainHeightSampler {
+  const { scene } = useGLTF(TERRAIN_MODEL_PATH);
+
+  return useMemo(() => createTerrainHeightSampler(scene), [scene]);
+}
+
+export function useTerrainSnappedPosition(
+  position: Vector3Tuple,
+): Vector3Tuple {
+  const terrainHeight = useTerrainHeightSampler();
+
+  return useMemo(() => {
+    const [x, y, z] = position;
+    const height = terrainHeight.getHeight(x, z);
+    return [x, height ?? y, z];
+  }, [position, terrainHeight]);
+}
+
+export function normalizeMapScale(scale: Vector3Tuple): Vector3Tuple {
+  const [x, y, z] = scale;
+  const isUniform = Math.abs(x - y) < 0.001 && Math.abs(x - z) < 0.001;
+  return isUniform ? scale : [x, x, x];
+}