three.js大场景模型下显存占用太高，会导致浏览器崩溃，给出详细解决代码

在three.js中，大场景模型下显存占用太高的问题，可以通过以下几种方法来解决：

1. 优化模型

可以通过优化模型来减小模型的大小，从而减小显存的占用。具体的优化方法包括：合并几何体、删除不必要的网格、压缩纹理等等。下面是一个示例代码：

// 合并几何体
var geometry = new THREE.Geometry();
scene.traverse(function(child) {
  if (child instanceof THREE.Mesh) {
    child.updateMatrix();
    geometry.merge(child.geometry, child.matrix);
  }
});
var mesh = new THREE.Mesh(geometry, material);
scene.add(mesh);

// 删除不必要的网格
var mesh = new THREE.Mesh(geometry, material);
mesh.castShadow = true;
mesh.receiveShadow = true;
mesh.frustumCulled = false;
scene.add(mesh);
scene.traverse(function(child) {
  if (child instanceof THREE.Mesh) {
    if (child !== mesh) {
      scene.remove(child);
    }
  }
});

// 压缩纹理
var texture = new THREE.TextureLoader().load('texture.jpg');
texture.minFilter = THREE.LinearMipMapLinearFilter;
texture.anisotropy = renderer.getMaxAnisotropy();

2. 分段加载模型

可以将大场景模型分成多个小模型，然后在需要的时候动态加载。具体的方法包括：使用LOD（层次细节对象）、使用Octree（八叉树）、使用Frustum Culling（锥体剔除）等等。下面是一个示例代码：

// 使用LOD
var lod = new THREE.LOD();
lod.addLevel(mesh1, 100);
lod.addLevel(mesh2, 200);
lod.addLevel(mesh3, 300);
scene.add(lod);

// 使用Octree
var octree = new THREE.Octree();
scene.traverse(function(child) {
  if (child instanceof THREE.Mesh) {
    octree.add(child);
  }
});
var objects = octree.search(camera.position, 1000);

// 使用Frustum Culling
var frustum = new THREE.Frustum();
frustum.setFromMatrix(new THREE.Matrix4().multiplyMatrices(camera.projectionMatrix, camera.matrixWorldInverse));
scene.traverse(function(child) {
  if (child instanceof THREE.Mesh) {
    if (frustum.intersectsObject(child)) {
      child.visible = true;
    } else {
      child.visible = false;
    }
  }
});

3. 减小渲染范围

可以通过减小渲染范围来减小显存的占用。具体的方法包括：使用裁剪平面、使用遮挡剔除等等。下面是一个示例代码：

// 使用裁剪平面
var plane = new THREE.Plane(new THREE.Vector3(0, 1, 0), -10);
var clipPlane = new THREE.ClipPlane(plane, camera);
renderer.clippingPlanes = [clipPlane];
renderer.localClippingEnabled = true;

// 使用遮挡剔除
var occluder = new THREE.Mesh(geometry, material);
occluder.position.set(0, 0, 0);
occluder.scale.set(10, 10, 10);
occluder.castShadow = false;
occluder.receiveShadow = false;
occluder.material.color.setHex(0x000000);
occluder.material.opacity = 0.5;
occluder.renderOrder = 0;
scene.add(occluder);
var occluderScene = new THREE.Scene();
occluderScene.add(camera);
occluderScene.add(occluder);
var renderer2 = new THREE.WebGLRenderer();
renderer2.setSize(width, height);
renderer2.autoClear = false;
renderer2.domElement.style.position = 'absolute';
renderer2.domElement.style.top = '0px';
renderer2.domElement.style.left = '0px';
document.body.appendChild(renderer2.domElement);
renderer2.render(occluderScene, camera);
renderer2.domElement.style.display = 'none';
renderer.setOpaqueSort(false);
renderer.domElement.addEventListener('mousedown', function(event) {
  var x = event.clientX;
  var y = event.clientY;
  var rect = event.target.getBoundingClientRect();
  x = ((x - rect.left) / rect.width) * 2 - 1;
  y = -((y - rect.top) / rect.height) * 2 + 1;
  var mouseVector = new THREE.Vector3(x, y, 0.5);
  mouseVector.unproject(camera);
  var raycaster = new THREE.Raycaster(camera.position, mouseVector.sub(camera.position).normalize());
  var intersects = raycaster.intersectObjects(scene.children, true);
  if (intersects.length > 0) {
    var object = intersects[0].object;
    renderer2.render(occluderScene, camera);
    var isOccluded = renderer2.domElement.getContext('webgl').isPointInPath(x, y);
    if (!isOccluded) {
      // do something
    }
  }
});