How to prevent interpolation of vertex colors in THREE.js shader?
I am trying to write a shader that draws contour plots on meshes.
Here is an example of contour plot.
My first aim is visualizing one triangle face with different colors. You can find the code that I am using in here.
<html lang="en">
<head>
<title>Face Contour Example</title>
</head>
<body>
<script src="http://threejs.org/build/three.min.js"></script>
<script src="http://threejs.org/examples/js/controls/OrbitControls.js"></script>
<script id="vertexShader" type="x-shader/x-vertex">
varying vec3 vColor;
void main(){
vColor = color;
gl_Position = projectionMatrix * modelViewMatrix * vec4(position, 1.0);
}
</script>
<script id="fragmentShader" type="x-shader/x-fragment">
varying vec3 vColor;
void main(){
gl_FragColor = vec4( vColor.rgb, 1.0 );
}
</script>
<script type="text/javascript">
var camera, scene, renderer, mesh, material, controls;
init();
animate();
function init() {
// Renderer.
renderer = new THREE.WebGLRenderer();
//renderer.setPixelRatio(window.devicePixelRatio);
renderer.setSize(window.innerWidth, window.innerHeight);
// Add renderer to page
document.body.appendChild(renderer.domElement);
// Create camera.
camera = new THREE.PerspectiveCamera(70, window.innerWidth / window.innerHeight, 1, 1000);
camera.position.z = -400;
// Create scene.
scene = new THREE.Scene();
var colors = {
"color1" : {
type : "c",
value : new THREE.Color(0xff0000) //r
},
"color2" : {
type : "c",
value : new THREE.Color(0x00ff00) //b
},
"color3" : {
type : "c",
value : new THREE.Color(0x0000ff) //g
},
};
var fShader = document.getElementById('fragmentShader').text;
var vShader = document.getElementById('vertexShader').text;
// Create material
var material = new THREE.ShaderMaterial({
vertexShader: vShader,
fragmentShader: fShader,
vertexColors: THREE.VertexColors,
});
// var material = new THREE.MeshBasicMaterial( { vertexColors: THREE.VertexColors } );
// Create cube and add to scene.
var geometry = new THREE.Geometry();
geometry.vertices=[
new THREE.Vector3(100,0,0),
new THREE.Vector3(-100,0,0),
new THREE.Vector3(50,100,0)
]
var face=new THREE.Face3();
face.a=0;
face.b=1;
face.c=2;
face.vertexColors[ 0 ] = colors["color1"].value;
face.vertexColors[ 1 ] = colors["color2"].value;
face.vertexColors[ 2 ] = colors["color3"].value;
geometry.faces=[face]
mesh = new THREE.Mesh(geometry, material);
scene.add(mesh);
function addWireFrame(){
//Create wireframe helper for mesh with same geometry
var wireframeMesh=new THREE.WireframeGeometry(geometry);
var line = new THREE.LineSegments( wireframeMesh );
line.material.depthTest = false;
line.material.opacity = 0.75;
line.material.transparent = true;
mesh.add( line );
}
addWireFrame();
//Orbit controls
controls = new THREE.OrbitControls( camera );
// Create ambient light and add to scene.
var light = new THREE.AmbientLight(0x404040); // soft white light
scene.add(light);
// Create directional light and add to scene.
var directionalLight = new THREE.DirectionalLight(0xffffff);
directionalLight.position.set(1, 1, 1).normalize();
scene.add(directionalLight);
// Add listener for window resize.
window.addEventListener('resize', onWindowResize, false);
}
function animate() {
requestAnimationFrame(animate);
controls.update();
renderer.render(scene, camera);
}
function onWindowResize() {
camera.aspect = window.innerWidth / window.innerHeight;
camera.updateProjectionMatrix();
renderer.setSize(window.innerWidth, window.innerHeight);
}
</script>
</body>
</html>
In the code I assigned red, green and blue colors to each vertices of a face.
In vertex shader, I redirected those colors to fragment shader. And In fragment shader, I am planning to use my own formula to decide which color will be used for that instance of the fragment. (My formula will depend on the position on the face.)
However, I couldn't manage to prevent interpolation of vertex colors. Is there a way to pick vertex color from an array directly without interpolation in three.js?
Also, I appreciate alternative solutions that may be suitable for my problem.
You don't want to disable interpolation. You want, instead, to use the interpolated coordinates as an index. The interpolated color value tells you how close you are to each of the vertices. You can then quantize this interpolated value into ranges, or indexes into a color array, to produce the end color.
I modified your fiddle to show the color of the closest vertex using the following pixel shader:
void main(){
vec3 c = vColor;
gl_FragColor = vec4(c.r > c.g && c.r > c.b ? 1.0 : 0.0,
c.g > c.r && c.g > c.b ? 1.0 : 0.0,
c.b > c.r && c.b > c.g ? 1.0 : 0.0,
1.0 );
}
The result looks like this:
You will need a more complex quantization method to show a contour map, but I hope this approach gives you a good start.