javascript - Apply color gradient to material on mesh - three.js

Question

I have an STL file loaded into my scene with a single colour applied to a phong material

I'd like a way of applying two colours to this mesh's material with a gradient effect applied on the Z axis a like the example below.Gradient Vase]1

I have a feeling I may have to introduce shaders but I've not gotten this far with three.js.

Answer 1

Simple gradient shader, based on uvs:

var scene = new THREE.Scene();
var camera = new THREE.PerspectiveCamera(60, 1, 1, 1000);
camera.position.set(13, 25, 38);
camera.lookAt(scene.position);
var renderer = new THREE.WebGLRenderer({
  antialias: true
});
var canvas = renderer.domElement
document.body.appendChild(canvas);

var controls = new THREE.OrbitControls(camera, renderer.domElement);

var geometry = new THREE.CylinderBufferGeometry(2, 5, 20, 32, 1, true);
var material = new THREE.ShaderMaterial({
  uniforms: {
    color1: {
      value: new THREE.Color("red")
    },
    color2: {
      value: new THREE.Color("purple")
    }
  },
  vertexShader: `
    varying vec2 vUv;

    void main() {
      vUv = uv;
      gl_Position = projectionMatrix * modelViewMatrix * vec4(position,1.0);
    }
  `,
  fragmentShader: `
    uniform vec3 color1;
    uniform vec3 color2;
  
    varying vec2 vUv;
    
    void main() {
      
      gl_FragColor = vec4(mix(color1, color2, vUv.y), 1.0);
    }
  `,
  wireframe: true
});
var mesh = new THREE.Mesh(geometry, material);
scene.add(mesh);



render();

function resize(renderer) {
  const canvas = renderer.domElement;
  const width = canvas.clientWidth;
  const height = canvas.clientHeight;
  const needResize = canvas.width !== width || canvas.height !== height;
  if (needResize) {
    renderer.setSize(width, height, false);
  }
  return needResize;
}

function render() {
  if (resize(renderer)) {
    camera.aspect = canvas.clientWidth / canvas.clientHeight;
    camera.updateProjectionMatrix();
  }
  renderer.render(scene, camera);
  requestAnimationFrame(render);
}

html,
body {
  height: 100%;
  margin: 0;
  overflow: hidden;
}

canvas {
  width: 100%;
  height: 100%;
  display;
  block;
}

<script src="https://cdn.jsdelivr.net/npm/[email protected]/build/three.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/[email protected]/examples/js/controls/OrbitControls.js"></script>