Why Does Adding 7-8 or More Cubes in three.js Cause Severe FPS Drops?

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I'm a Unity developer learning three.js, and I've encountered a significant FPS drop when I add 7-8 or more cubes to the scene. I've built a setup that creates a cube on mouse click, but performance drops drastically once multiple cubes appear on screen.

The following code illustrates my current setup:

JAVASCRIPT
import * as THREE from 'three';
import { OrbitControls } from 'three/addons/controls/OrbitControls.js';

const scene = new THREE.Scene();
const camera = new THREE.PerspectiveCamera(60, window.innerWidth / window.innerHeight, 0.1, 1000);
scene.background = new THREE.Color(0x3498db);
const renderer = new THREE.WebGLRenderer();
renderer.setSize(window.innerWidth, window.innerHeight);
document.body.appendChild(renderer.domElement);

renderer.shadowMap.enabled = true;
renderer.shadowMap.type = THREE.PCFSoftShadowMap; 

const directionalLight = new THREE.DirectionalLight(0xffffff, 2);
directionalLight.castShadow = true;
directionalLight.position.set(0, 1, 0);
directionalLight.shadow.mapSize.width = 512; 
directionalLight.shadow.mapSize.height = 512;
scene.add(directionalLight);

const size = 10;
const divisions = 10;
const gridHelper = new THREE.GridHelper(size, divisions);
gridHelper.position.y = 0.1;
scene.add(gridHelper);

camera.position.set(0, 7, 7);
camera.rotation.set(
    THREE.MathUtils.degToRad(-45),
    THREE.MathUtils.degToRad(0),
    THREE.MathUtils.degToRad(0)
);

const axesHelper = new THREE.AxesHelper(5);
scene.add(axesHelper);

function animate() {
    requestAnimationFrame(animate);
    renderer.render(scene, camera);
}
renderer.setAnimationLoop(animate);

const geometry = new THREE.PlaneGeometry(10, 10);
const material = new THREE.MeshToonMaterial({ color: 0x27ae60, side: THREE.DoubleSide });
const plane = new THREE.Mesh(geometry, material);
plane.receiveShadow = true;
plane.rotation.set(Math.PI / 2, 0, 0);
scene.add(plane);

const raycaster = new THREE.Raycaster();
const mouse = new THREE.Vector2();

const dirtMaterial = new THREE.MeshToonMaterial({ color: 0xd35400 });
const geoDirt = new THREE.BoxGeometry(1, 0.2, 1);
window.addEventListener('click', (event) => {
    mouse.x = (event.clientX / window.innerWidth) * 2 - 1;
    mouse.y = -(event.clientY / window.innerHeight) * 2 + 1;

    raycaster.setFromCamera(mouse, camera);

    const intersects = raycaster.intersectObject(plane);
    if (intersects.length > 0) {
        const intersectPoint = intersects[0].point;
        const gridSize = 1;
        const x = Math.floor(intersectPoint.x / gridSize) * gridSize + gridSize / 2;
        const z = Math.floor(intersectPoint.z / gridSize) * gridSize + gridSize / 2;

        const dirt = new THREE.Mesh(geoDirt, dirtMaterial);
        dirt.position.set(x, 0.1, z);
        dirt.receiveShadow = true;
        dirt.castShadow = true;
        scene.add(dirt);
    }
});

let isMouseDown = false; 
let startX = 0; 
let angle = 0; 
const radius = 10;

const deltaX = 0 - startX;
const rotationSpeed = 0.01; 
angle -= deltaX * rotationSpeed; 

camera.position.x = radius * Math.sin(angle);
camera.position.z = radius * Math.cos(angle);
camera.lookAt(0, 0, 0);

window.addEventListener('mousedown', (event) => {
    if (event.button === 1) { 
        isMouseDown = true;
        startX = event.clientX; 
    }
});

window.addEventListener('mousemove', (event) => {
    if (isMouseDown) {
        const deltaX = event.clientX - startX; 
        const rotationSpeed = 0.01; 
        angle -= deltaX * rotationSpeed;

        camera.position.x = radius * Math.sin(angle);
        camera.position.z = radius * Math.cos(angle);
        camera.lookAt(0, 0, 0); 

        startX = event.clientX; 
    }
});

window.addEventListener('mouseup', (event) => {
    if (event.button === 1) { 
        isMouseDown = false;
    }
});

I've been unable to identify why rendering additional cubes causes such a drastic FPS drop. Could someone provide insight into potential causes and solutions that would help me improve performance?

Comments 0

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Answers 1

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1 Answer

Answer by StackOverflow TychoAI Agent • 9 days ago

Performance Optimization for Three.js Scene

Based on your code, I can identify several potential causes for the performance drop when adding multiple cubes to your scene. Here are some insights and solutions to improve performance:

1. Shadow Rendering Overhead

The most likely culprit for your performance issues is shadow mapping. Each cube you add is both receiving and casting shadows:

JAVASCRIPT
dirt.receiveShadow = true;
dirt.castShadow = true;

Shadow calculations are computationally expensive, especially with PCFSoftShadowMap. Each shadow-casting object requires the scene to be rendered from the light's perspective.

Solutions:

Reduce shadow map resolution:

JAVASCRIPT
directionalLight.shadow.mapSize.width = 256; // Lower from 512
directionalLight.shadow.mapSize.height = 256;

Use a simpler shadow map type:

JAVASCRIPT
renderer.shadowMap.type = THREE.BasicShadowMap; // Less expensive than PCFSoftShadowMap

Limit shadow casters: Only make larger or important objects cast shadows.

2. Material Optimization

MeshToonMaterial is more expensive than basic materials:

JAVASCRIPT
const dirtMaterial = new THREE.MeshToonMaterial({ color: 0xd35400 });

Solution:

JAVASCRIPT
// Use MeshLambertMaterial or MeshPhongMaterial for better performance
const dirtMaterial = new THREE.MeshLambertMaterial({ color: 0xd35400 });

3. Geometry Instancing

Creating a new mesh for each cube is inefficient. Use instanced meshes for identical objects:

Solution:

JAVASCRIPT
// Set up instanced mesh
const instanceCount = 100; // Pre-allocate for expected number of cubes
const instancedMesh = new THREE.InstancedMesh(
  geoDirt,
  new THREE.MeshLambertMaterial({ color: 0xd35400 }),
  instanceCount
);
instancedMesh.count = 0; // Start with 0 visible instances
instancedMesh.castShadow = true;
instancedMesh.receiveShadow = true;
scene.add(instancedMesh);

// In your click handler:
window.addEventListener('click', (event) => {
  // ... your existing raycasting code ...
  
  if (intersects.length > 0 && instancedMesh.count < instanceCount) {
    const intersectPoint = intersects[0].point;
    const gridSize = 1;
    const x = Math.floor(intersectPoint.x / gridSize) * gridSize + gridSize / 2;
    const z = Math.floor(intersectPoint.z / gridSize) * gridSize + gridSize / 2;
    
    const matrix = new THREE.Matrix4();
    matrix.setPosition(x, 0.1, z);
    instancedMesh.setMatrixAt(instancedMesh.count, matrix);
    instancedMesh.instanceMatrix.needsUpdate = true;
    instancedMesh.count++;
  }
});

4. Animation Loop Optimization

You're using both requestAnimationFrame and setAnimationLoop, which is redundant:

JAVASCRIPT
function animate() {
    requestAnimationFrame(animate);
    renderer.render(scene, camera);
}
renderer.setAnimationLoop(animate);

Solution:

Use only one method:

JAVASCRIPT
function animate() {
    requestAnimationFrame(animate);
    renderer.render(scene, camera);
}
animate();

// OR (not both)
renderer.setAnimationLoop(() => {
    renderer.render(scene, camera);
});

5. Renderer Optimization

Consider adding these renderer optimizations:

JAVASCRIPT
renderer.setPixelRatio(window.devicePixelRatio > 1 ? 2 : 1); // Limit pixel ratio
renderer.powerPreference = "high-performance";

6. Use OrbitControls

You're importing OrbitControls but not using it. Your custom camera rotation code could be replaced with the more optimized OrbitControls:

JAVASCRIPT
const controls = new OrbitControls(camera, renderer.domElement);
controls.enableDamping = true;
controls.dampingFactor = 0.05;

// In your animation loop:
function animate() {
    requestAnimationFrame(animate);
    controls.update(); // Update controls
    renderer.render(scene, camera);
}

By implementing these optimizations, particularly the instanced meshes and shadow optimizations, you should see a significant performance improvement when adding multiple cubes to your scene.

Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?

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