Three.js "mixed mode": DOM element with shadow and shine.

index.html

<script src="https://threejs.org/build/three.min.js"></script>
<script src="https://threejs.org/examples/js/controls/OrbitControls.js"></script>
<script src="https://threejs.org/examples/js/renderers/CSS3DRenderer.js"></script>

<div id="css"></div>
<div id="webgl"></div>

script.babel

var camera, root, scene, renderer, renderer2, windowHalfX, windowHalfY, background;
var mouseX = 0, mouseY = 0;
var sphere;
var light
var lightMovementAmplitude = 200

init();
animate(performance.now());

function init() {

    windowHalfX = window.innerWidth / 2;
    windowHalfY = window.innerHeight / 2;

    camera = new THREE.PerspectiveCamera(
        45, window.innerWidth / window.innerHeight, 1, 2000
    );
    camera.position.set( 0, 0, 500 );

    scene = new THREE.Scene()
    root = new THREE.Object3D()
    root.position.y = 20
    root.rotation.y = Math.PI / 3
    scene.add(root)
    
    background = makeElementObject('div', 200, 200)
    background.css3dObject.element.textContent = "How can we make the Sphere show behind this surface?"
    background.css3dObject.element.setAttribute('contenteditable', '')    
    background.position.z = 20
    background.css3dObject.element.style.opacity = "0.65"
    root.add( background );
    
    const button = makeElementObject('button', 75, 20)    
    button.css3dObject.element.style.border = '1px solid orange'
    button.css3dObject.element.textContent = "Click me!"
    button.css3dObject.element.addEventListener('click', () => alert('Button clicked!'))
    button.position.y = 10
    button.position.z = 10
    background.add(button)

    // make a geometry to see if we can clip it with the DOM elememt.
    ~function() {
        var material = new THREE.MeshPhongMaterial({
            color: 0x156289,
            emissive: 0x000000,
            specular: 0x111111,
            side: THREE.DoubleSide,
            flatShading: false,
            shininess: 30,
        })
        var geometry = new THREE.SphereGeometry( 70, 32, 32 );
        sphere = new THREE.Mesh( geometry, material );
        sphere.position.z = 20;
        sphere.position.y = -100;
        sphere.castShadow = true;
        sphere.receiveShadow = false;
        root.add( sphere );
    }()

    // light
    ~function() {
        var ambientLight = new THREE.AmbientLight( 0x999999 );
        root.add( ambientLight );

        light = new THREE.PointLight( 0xffffff, 1, 0 );
        light.castShadow = true;
        light.position.z = 150;
        light.shadow.mapSize.width = 512;  // default
        light.shadow.mapSize.height = 512; // default
        light.shadow.camera.near = 1;       // default
        light.shadow.camera.far = 2000;      // default
        
        scene.add( new THREE.PointLightHelper( light, 10 ) )

        root.add( light );
    }()

    renderer2 = new THREE.CSS3DRenderer();
    renderer2.setSize( window.innerWidth, window.innerHeight );
    renderer2.domElement.style.position = 'absolute';
    renderer2.domElement.style.top = 0;
    document.querySelector('#css').appendChild( renderer2.domElement );

    renderer = new THREE.WebGLRenderer({ alpha: true, antialias: true });
    renderer.setClearColor( 0x000000, 0 );
    renderer.setPixelRatio( window.devicePixelRatio );
    renderer.setSize( window.innerWidth, window.innerHeight );
    renderer.shadowMap.enabled = true;
    renderer.shadowMap.type = THREE.PCFSoftShadowMap; // default THREE.PCFShadowMap
    document.querySelector('#webgl').appendChild( renderer.domElement );

    document.addEventListener( 'mousemove', onDocumentMouseMove, false );

}

function onDocumentMouseMove( event ) {
    mouseX = event.clientX - windowHalfX;
    mouseY = event.clientY - windowHalfY;
}

function animate(time) {
    
    light.position.x = 20 * Math.sin(time * 0.003);
    light.position.y = 40 * Math.cos(time * 0.002) - 80;
    background.rotation.y = Math.PI/8 * Math.cos(time * 0.001) - Math.PI/6;
    background.rotation.x = Math.PI/10 * Math.sin(time * 0.001) - Math.PI/10;

    scene.updateMatrixWorld()

    renderer.render( scene, camera );
    renderer2.render( scene, camera );

    requestAnimationFrame( animate );
}

function makeElementObject(type, width, height) {
    const obj = new THREE.Object3D

    const element = document.createElement( type );
    element.style.width = width+'px';
    element.style.height = height+'px';
    element.style.opacity = 0.999;
    element.style.background = new THREE.Color(
        Math.random() * 0.21568627451 + 0.462745098039,
        Math.random() * 0.21568627451 + 0.462745098039,
        Math.random() * 0.21568627451 + 0.462745098039,
    ).getStyle();


    var css3dObject = new THREE.CSS3DObject( element );
    obj.css3dObject = css3dObject
    obj.add(css3dObject)

    // make an invisible plane for the DOM element to chop
    // clip a WebGL geometry with it.
    var material = new THREE.MeshPhongMaterial({
        opacity	: 0.15,
        color	: new THREE.Color( 0x111111 ),
        blending: THREE.NoBlending,
        side	: THREE.DoubleSide,
    });
    var geometry = new THREE.BoxGeometry( width, height, 1 );
    var mesh = new THREE.Mesh( geometry, material );
    mesh.castShadow = true;
    mesh.receiveShadow = true;
    obj.lightShadowMesh = mesh
    obj.add( mesh );

    return obj
}

style.css

body {
    background-color: #ffffff;
    margin: 0;
    overflow: hidden;
}

* {
    outline: none;
}

#css, #webgl {
    width: 100%;
    height: 100%;
    position: absolute;
    top: 0; left: 0;
}

#css {
    background: repeating-linear-gradient(
        45deg,
        #606dbc,
        #606dbc 10px,
        #465298 10px,
        #465298 20px
    );

}

#webgl {
  pointer-events: none;
}

three-js-mixed-mode-dom-element-with-shadow-and-shine.markdown

Three.js "mixed mode": DOM element with shadow and shine.

A Pen by Joe Pea on CodePen.

License.

That demo probably broke due to un-versioned script URLs. Use these instead:

<script src="https://unpkg.com/[email protected]/build/three.min.js"></script>
<script src="https://unpkg.com/[email protected]/examples/js/controls/OrbitControls.js"></script>
<script src="https://unpkg.com/[email protected]/examples/js/renderers/CSS3DRenderer.js"></script>