Mesh

• geometry and material are public properties; replacing geometry does not dispose the old one.
• castShadow and receiveShadow decide participation in shadow map rendering.
• raycast() is invoked by Raycaster and returns intersection records for picking.

const geometry = new THREE.BoxGeometry(1.2, 2.4, 1.2);
const material = new THREE.MeshStandardMaterial({
  color: 0x4f9ef8,
  roughness: 0.4,
  metalness: 0.1
});

const mesh = new THREE.Mesh(geometry, material);
mesh.position.set(10, 1.2, -6);
mesh.rotation.y = Math.PI / 6;
mesh.castShadow = true;
mesh.receiveShadow = true;

scene.add(mesh);

const mats = [
  new THREE.MeshStandardMaterial({ color: 0xb9c3cc }),
  new THREE.MeshPhysicalMaterial({ color: 0x9fd8ff, roughness: 0.1, metalness: 0 })
];

const mesh = new THREE.Mesh(geometry, mats);
// 每个分组一次绘制调用，材质越多，调用数越高

• clone() copies references, so editing the cloned mesh's material also changes the original.
• Replacing geometry repeatedly leaks GPU buffers unless the previous one is disposed.