Three.js DoubleSided does not cast shadow on both sides of planar parametric geometry

Question

See this jfiddle: http://jsfiddle.net/blwoodley/5Tr4D/1/

I have a blue spot of light that shines on a rotating spinning square. It casts a shadow on the underlying ground. Except that he only casts a shadow on one side of the square.

I saw this discussion: https://github.com/mrdoob/three.js/issues/3544 , which indicates that eliminating the face on flat surfaces is the cause. the recommendation is to give my square some depth, i.e. make it a cube.

I can do this with this simple example, but I am facing the same problem with parametric geometry, which is a surface. Is there a way to make both sides cast a shadow without giving my geometry a depth that isn't or is needed?

Here is the main script function that replicates the problem using a plane:

function init() {

container = document.createElement('div');
document.body.appendChild(container);

camera = new THREE.PerspectiveCamera(30, window.innerWidth / window.innerHeight, 1, 100000);
camera.position.x = 100;
camera.position.y = 100;
camera.position.z = 100;
camera.lookAt({x: 0,y: 0,z: 0});

scene = new THREE.Scene();

var groundMaterial = new THREE.MeshLambertMaterial({
    color: 0xffffff, side:THREE.DoubleSide 
});
plane = new THREE.Mesh(new THREE.PlaneGeometry(2000,2000,10,10), groundMaterial);
plane.rotation.x = Math.PI / 2;
plane.position.y = -40;
plane.receiveShadow = true;

scene.add(plane);

var light;

light = new THREE.SpotLight(0x0000ff);
light.position.set(40, 40, 0);
light.castShadow = true;
light.shadowCameraVisible = true;
light.shadowMapWidth = 2048;
light.shadowMapHeight = 2048;
light.position.set(24, 20, 0);
light.lookAt(plane);    
light.castShadow = true;
light.angle = .8;
light.intensity = 30;
light.distance=0;
light.shadowCameraNear = 2;
light.shadowCameraFar = 100;
light.shadowCameraFov = 100;
light.shadowDarkness = 1;
light.shadowCameraVisible = true;
scene.add(light);

var planeGeo = new THREE.PlaneGeometry(20,20,20,20)
_planeMesh = new THREE.Mesh(planeGeo, new THREE.MeshLambertMaterial( { color: 0x00ff00, side:THREE.DoubleSide } ) );
_planeMesh.castShadow = true;
scene.add( _planeMesh );


// RENDERER
webglRenderer = new THREE.WebGLRenderer();
webglRenderer.setSize(SCREEN_WIDTH, SCREEN_HEIGHT);
webglRenderer.domElement.style.position = "relative";
webglRenderer.shadowMapEnabled = true;
webglRenderer.shadowMapSoft = true;

container.appendChild(webglRenderer.domElement);
window.addEventListener('resize', onWindowResize, false);

}

Answer 1

Yes, this is a feature.

WebGLRenderer, by default, casts front edges when rendering shadows. This is normal because it is assumed that objects have depth. Instead, you can throw faces back if you want:

renderer.shadowMapCullFace = THREE.CullFaceBack;

... but culling is not an option.

The property is material.sidenot taken into account when casting shadows.

three.js r.63