Standard Full Screen Quad Setup not Working in Three.js

Question

I'm trying to establish a full screen quad using a pass thru vertex shader in THREE.js. The quad itself is a plane geometry with dimension (2, 2) located at the origin. It is assigned the ShaderMaterial. The camera is at z = 1 aiming at the quad.

The shaders are quite simple:

Vertex Shader:

void main() {
   gl_Position = vec4( position, 1.0 );
}

Fragment Shader:

void main() {
   gl_FragColor = vec4(0.0, 1.0, 0.0, 1.0);
}

But nothing shows up on screen. This setup is a standard way of render-to-texture, why is it not working in THREE.js?

I've tried plane.frustumCulled = false and changing the clip planes of the camera to no avail.

Any help is appreciated.

---

Upon further investigation, the reason for not seeing the rendering result is more involved and pointing to some odd behavior in three.js.

I am using a PlaneGeometry with a rotation matrix applied, which is then wrapped by an Object3D with a counter rotation.

var geometry = new THREE.PlaneGeometry(2, 2);
var m4 = new THREE.Matrix4().makeRotationX(Math.PI * 0.5);
geometry.applyMatrix(m4);

var mesh = new THREE.Mesh(geometry, material);
var obj = new THREE.Object3D();
obj.add(mesh);
obj.rotation.x = -Math.PI * 0.5;
scene.add(obj);

This setup seems to throw three.js off and no rendering is shown.

---

Ok, the rotation got thrown away because it is a part of model view matrix that I ignored in the vertex shader. I've to refact what I'm currently doing.

Answer 1

I'm not sure the exact problem you're having, but here is an example of a working fullscreen quad using the same technique.

var canvas = document.getElementById('canvas');
var scene = new THREE.Scene();
var renderer = new THREE.WebGLRenderer({canvas: canvas, antialias: true});
var camera = new THREE.PerspectiveCamera(45, canvas.clientWidth / canvas.clientWidth, 1, 1000);
var clock = new THREE.Clock();

var quad = new THREE.Mesh(
  new THREE.PlaneGeometry(2, 2),
  new THREE.ShaderMaterial({
    vertexShader: document.getElementById('vertex-shader').textContent,
    fragmentShader: document.getElementById('fragment-shader').textContent,
    depthWrite: false,
    depthTest: false
  })
);
scene.add(quad);

var box = new THREE.Mesh(
  new THREE.BoxGeometry(50, 50, 50),
  new THREE.MeshBasicMaterial({color: '#000', wireframe: true})
);
scene.add(box);

camera.position.z = 200;

render();

function render() {
  requestAnimationFrame(render);
  
  if (canvas.width !== canvas.clientWidth || canvas.height !== canvas.clientHeight) {
    renderer.setSize(canvas.clientWidth, canvas.clientHeight, false);
    camera.aspect = canvas.clientWidth /  canvas.clientHeight;
    camera.updateProjectionMatrix();
  }
  
  var dt = clock.getDelta();
  box.rotation.x += dt * 2 * Math.PI / 5;
  box.rotation.y += dt * 2 * Math.PI / 7;
  box.rotation.z += dt * 2 * Math.PI / 11;
  
  renderer.render(scene, camera);
}

html, body, #canvas {
  margin: 0;
  padding: 0;
  width: 100%;
  height: 100%;
  display: block;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/three.js/r73/three.min.js"></script>
<canvas id="canvas"></canvas>
<script id="vertex-shader" type="x-shader/x-vertex">
  varying vec2 vUv;

  void main() {
    vUv = uv;
    gl_Position = vec4(position, 1.0);
  }
</script>
<script id="fragment-shader" type="x-shader/x-fragment">
  varying vec2 vUv;

  void main() {
    gl_FragColor = vec4(vUv, 0.0, 1.0);
  }
</script>