как добавить градиент на фон канваса в этой сцене?
import * as THREE from 'three';
import { GLTFLoader } from 'three/examples/jsm/loaders/GLTFLoader';
import { OrbitControls } from 'three/examples/jsm/controls/OrbitControls'

const scene = new THREE.Scene();
const camera = new THREE.PerspectiveCamera(75, window.innerWidth / window.innerHeight, 0.1, 1000);
camera.position.z = 5;

const renderer = new THREE.WebGLRenderer();
renderer.setSize(window.innerWidth, window.innerHeight);
document.body.appendChild(renderer.domElement);

const controls = new OrbitControls( camera, renderer.domElement );
controls.enableZoom = false;

controls.enableDamping = true; 
controls.dampingFactor = 0.05; 


const loader = new GLTFLoader();
const url = 'GRAF_3_14.glb';

loader.load(url, function (gltf) {
  const model = gltf.scene;

  model.traverse((child) => {
    if (child.isMesh) {
      const geometry = child.geometry;

      const texture = new THREE.TextureLoader().load('Ellipse 2.png');

      let startSize = 0.03;
      const sizeVariation = 0.1;

      const materialPoint = new THREE.PointsMaterial({
        size: startSize,
        sizeAttenuation: true,
        map: texture,
        alphaTest: 0.01,
        transparent: true,
        color: new THREE.Color(1.8, 1.8, 1.8)
        //opacity: 0.4
      });

      const geometryPoint = new THREE.BufferGeometry();

      const positions = geometry.getAttribute('position').array;

      const randomSize = [];

      for (let i = 0; i < positions.length; i += 3) {
        const size = startSize + (Math.random() * sizeVariation);
        randomSize.push(size, size, size);
      }

      geometryPoint.setAttribute('size', new THREE.Float32BufferAttribute(randomSize, 1));

      const randomPosition = [];
      for (let i = 0; i < positions.length; i += 3) {
        randomPosition.push(10.0*Math.random()-5.0, 10.0*Math.random()-5.0, 10.0*Math.random()-5.0);
      }
      const randomPositionCopy = [...randomPosition];

      let increment = 0.002;
   
      geometryPoint.setAttribute('position', new THREE.Float32BufferAttribute(positions, 3));

      const points = new THREE.Points(geometryPoint, materialPoint);


      geometry.setAttribute('position', new THREE.BufferAttribute(new Float32Array(randomPosition), 3));
      function updateArray(increment) {
        for(let j = 0; j < 75; j++) {
          for(let i = 0; i<randomPosition.length; i++) {
            if (randomPosition[i] < positions[i]) {
              randomPosition[i] = randomPosition[i] + increment;
            } else if(randomPosition[i] > positions[i]) {
              randomPosition[i] = randomPosition[i] - increment;
            } else if((randomPosition[i] - positions[i]) < 0.002) {
              randomPosition[i] = positions[i];
            }
          }
        }
        geometryPoint.setAttribute('position', new THREE.BufferAttribute(new Float32Array(randomPosition), 3));
      }
      function reverseUpdateArray(increment) {
        for(let j = 0; j < 75; j++) {
          for(let i = 0; i<randomPosition.length; i++) {
            if (randomPosition[i] < randomPositionCopy[i]) {
              randomPosition[i] = randomPosition[i] + increment;
            } else if(randomPosition[i] > randomPositionCopy[i]) {
              randomPosition[i] = randomPosition[i] - increment;
            } else if((randomPosition[i] - randomPositionCopy[i]) < 0.002) {
              randomPosition[i] = randomPositionCopy[i];
            }
          }
        }
        geometryPoint.setAttribute('position', new THREE.BufferAttribute(new Float32Array(randomPosition), 3));
      }

      let time = 0;
      let sinPosition;
      let sinPosition2;
      let cosPosition;
      let randSignArray = [];
      let sign;
      let ratio = 1.0;

      for(let i = 0; i<randomPosition.length; i++) {
        sign = Math.random() < 0.5 ? -1.0 : 1.0;
        randSignArray[i] = sign;
      }

      animateVerticles();
      function animateVerticles() {
        requestAnimationFrame(animateVerticles);
        time += 0.1;
        sinPosition = Math.sin(time)*0.1;
        cosPosition = Math.cos(time*0.1)*0.1;
        sinPosition2 = Math.sin(time/Math.PI)*0.1;
        for(let i = 0; i<randomPosition.length; i++) {
          randomPosition[i] += (sinPosition * cosPosition * sinPosition2) * randSignArray[i] * ratio;
        }
        geometryPoint.setAttribute('position', new THREE.BufferAttribute(new Float32Array(randomPosition), 3));
      }

      window.addEventListener('wheel', function(event) {
        if (event.deltaY > 0) {
          updateArray(increment);
          if(ratio > 0.0) {
            ratio -= 0.01;
          }
        } else {
          reverseUpdateArray(increment);
          ratio += 0.01;
        }
        console.log(ratio);

      });

      scene.add(points);
      points.rotateX(Math.PI/2.0);
    }
  });
  camera.position.z = 3;
  
  function animate() {
  requestAnimationFrame(animate);
  controls.update();
  renderer.render(scene, camera);
  }
  animate();
});