Gabriel A. Zorrilla Gabriel A. Zorrilla - 9 days ago 5
Javascript Question

Threejs: Can I change a face color in PlaneGeometry based on vertex value?

Is there a way to programatically change the color of a face than pre-creating a pallet of materials and then assign based on the vertex value? I have this:

var materials = [];
materials.push([..] //add all the materials here.

var geometry = new THREE.PlaneGeometry(gs, gs, size, size);
$.getJSON('http://localhost:5000', function (data) {
for (var i = 0, l = geometry.vertices.length; i < l; i++) {
geometry.vertices[i].z = data.map[i] / 255;
if (geometry.vertices[i].z > 1) {
geometry.faces[i].materialIndex = 1;
} else {
geometry.faces[i].materialIndex = 0;
}
}
var plane = new THREE.Mesh(geometry, new THREE.MeshFaceMaterial(materials));
scene.add(plane);
});


Would like something like:

[..]
$.getJSON('http://localhost:5000', function (data) {
for (var i = 0, l = geometry.vertices.length; i < l; i++) {
geometry.vertices[i].z = data.map[i] / 255;
if (geometry.vertices[i].z > 1) {
geometry.faces[i].setrgb(i*128, i*2, i*96);
} else {
geometry.faces[i].setrgb(i*12, i*2, i*96);
}
}
[..]


Thanks!

Answer

As an example

var size = 10; // just for example
...
planeGeom = new THREE.PlaneGeometry(size, size, 10, 10);
...
planeGeom.faces.forEach(function(face){
  var val = planeGeom.vertices[face.a].y;
  face.color.setRGB(Math.abs(val) / size * 2, 0, 0);
});
planeGeom.colorsNeedUpdate = true;

if you want to set color with r, g, b components, then values of components must be from 0 to 1, not from 0 to 255. Each face is of Face3 type, which has properties a, b, c, where indices of vertices stored.

jsfiddle

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