Three.js University create shadow

Creating shadows with Three.js

To create shadows in Three.js, we need a few things :

  • A rendering engine capable of creating shadows
  • An appropriate lighting
  • A 3D object capable of creating a shadow
  • A 3D object capable of receiving a shadow

The shadowMap.enabled property of WebGLRenderer

Our 3D renderer shall be able to handle shadows ! For this, it is necessary to set the shadowMap.enabled property of our WebGLRenderer to true.

// ---------------- RENDERER ----------------
renderer = new THREE.WebGLRenderer( { antialias : true } );
renderer.setPixelRatio( window.devicePixelRatio  );
renderer.setSize( window.innerWidth, window.innerHeight );
renderer.shadowMap.enabled = true;         // IMPORTANT FOR SHADOWS !!!
document.body.appendChild( renderer.domElement );
Three.js University shadowMap.enabled
WebGLRenderer – shadowMap.enabled

Choose and configure lighting

To create shadows, we must use appropriate lighting.
Indeed, not all lights are able to create shadows ! In this example we will use the PointLight class.

Note that the DirectionalLight class of our Hello World can also create shadows !

const color = 0xFFFFFF;
const intensity = 0.5;
light = new THREE.PointLight(color, intensity);
light.castShadow = true;         // IMPORTANT FOR SHADOWS !!!
light.position.set(0, 10, 0);

We set the castShadow property of our lighting to true, to allow it to create shadows.

Three.js University light castShadow
Light – castShadow

Configure our 3D objects

Receiving a shadow – receiveShadow

When we want to create shadows, it is essential to define a surface able to receive them !
In our example, we will use a Mesh based on a PlaneGeometry structure.

const planeGeo = new THREE.PlaneGeometry(100, 100);
const planeMat = new THREE.MeshPhongMaterial({ color : 'white',side: THREE.DoubleSide});
const meshplane = new THREE.Mesh(planeGeo, planeMat);
meshplane.receiveShadow = true;            // IMPORTANT FOR SHADOWS !!!
meshplane.rotation.x = Math.PI /2;

The receiveShadow (Boolean) property of the Mesh class defines if the object is able to receive a cast shadow.
To allow our 3D object to receive shadows, we set this value to true.

Three.js University Mesh receiveShadow
Mesh – receiveShadow

Casting a shadow – castShadow

Finally, let’s create 3D objects that can produce a shadow. The cast shadow will be visible on the surfaces capable of receiving it, as mentioned in the previous paragraph.

To allow a Mesh to cast a shadow, we use its castShadow property (Boolean).

const cubeGeo = new THREE.BoxGeometry(2, 2, 2);
const cubeMat = new THREE.MeshPhongMaterial({color: '#8AC'});
const meshcube = new THREE.Mesh(cubeGeo, cubeMat);
meshcube.castShadow = true;            // IMPORTANT FOR SHADOWS !!!
meshcube.position.set(5, 1, 5);

Thus, by setting the value of this property to true, the concerned object will be able to cast shadows under the effect of an adapted light source.

Three.js University Mesh castShadow
Mesh – castShadow

Note that a Mesh is able to receive and create shadows at the same time : It is possible to set the castShadow and receiveShadow properties of the same object to true !

Final Result

See the Pen Shadows by Thomas (@thomassifferlen) on CodePen.

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