src/XKTModel/lib/buildVertexNormals.js
import {math} from "./math.js";
/**
* Builds vertex normal vectors from positions and indices.
*
* @private
*/
function buildVertexNormals(positions, indices, normals) {
const a = math.vec3();
const b = math.vec3();
const c = math.vec3();
const ab = math.vec3();
const ac = math.vec3();
const crossVec = math.vec3();
const nvecs = new Array(positions.length / 3);
for (let i = 0, len = indices.length; i < len; i += 3) {
const j0 = indices[i];
const j1 = indices[i + 1];
const j2 = indices[i + 2];
a[0] = positions[j0 * 3];
a[1] = positions[j0 * 3 + 1];
a[2] = positions[j0 * 3 + 2];
b[0] = positions[j1 * 3];
b[1] = positions[j1 * 3 + 1];
b[2] = positions[j1 * 3 + 2];
c[0] = positions[j2 * 3];
c[1] = positions[j2 * 3 + 1];
c[2] = positions[j2 * 3 + 2];
math.subVec3(b, a, ab);
math.subVec3(c, a, ac);
const normVec = math.vec3();
math.normalizeVec3(math.cross3Vec3(ab, ac, crossVec), normVec);
if (!nvecs[j0]) {
nvecs[j0] = [];
}
if (!nvecs[j1]) {
nvecs[j1] = [];
}
if (!nvecs[j2]) {
nvecs[j2] = [];
}
nvecs[j0].push(normVec);
nvecs[j1].push(normVec);
nvecs[j2].push(normVec);
}
normals = (normals && normals.length === positions.length) ? normals : new Float32Array(positions.length);
for (let i = 0, len = nvecs.length; i < len; i++) { // Now go through and average out everything
const count = nvecs[i].length;
let x = 0;
let y = 0;
let z = 0;
for (let j = 0; j < count; j++) {
x += nvecs[i][j][0];
y += nvecs[i][j][1];
z += nvecs[i][j][2];
}
normals[i * 3] = (x / count);
normals[i * 3 + 1] = (y / count);
normals[i * 3 + 2] = (z / count);
}
return normals;
}
export {buildVertexNormals};