@polygonjs/polygonjs/src/core/geometry/modules/cad/toObject3D/CadTriangulationFaceUtils.ts

node-based WebGL 3D engine https://polygonjs.com

import type {FaceData, OpenCascadeInstance, TopoDS_Face} from '../CadCommon';
import {CadGC} from '../CadCommon';
import {CadLoaderSync} from '../CadLoaderSync';
enum FaceOrientation {
	BACKWARD = 0,
	FORWARD = 1,
}
function faceOrientation(oc: OpenCascadeInstance, face: TopoDS_Face): FaceOrientation {
	return face.Orientation_1() === oc.TopAbs_Orientation.TopAbs_FORWARD
		? FaceOrientation.FORWARD
		: FaceOrientation.BACKWARD;
}
const STRIDE = 3;
export function faceData(oc: OpenCascadeInstance, face: TopoDS_Face, index0 = 0): FaceData | void {
	return CadGC.withGC((r) => {
		const location = CadLoaderSync.TopLoc_Location;
		const triangulation = oc.BRep_Tool.Triangulation(face, location, 0);

		if (triangulation.IsNull()) {
			return;
		}

		const transformation = location.Transformation();
		const tri = triangulation.get();
		const nbNodes = tri.NbNodes();

		// init
		const normalsArray = r(new oc.TColgp_Array1OfDir_2(1, nbNodes));
		const pc = r(new oc.Poly_Connect_2(triangulation));
		oc.StdPrs_ToolTriangulatedShape.Normal(face, pc, normalsArray);
		const nbTriangles = tri.NbTriangles();
		const faceData: FaceData = {
			positions: new Array(nbNodes * 3),
			normals: new Array(normalsArray.Length() * 3),
			indices: new Array(nbTriangles * 3),
		};

		// positions
		for (let i = 1; i <= nbNodes; i++) {
			const p = tri.Node(i).Transformed(transformation);
			const index = (i - 1) * STRIDE;
			faceData.positions[index] = p.X();
			faceData.positions[index + 1] = p.Y();
			faceData.positions[index + 2] = p.Z();
		}

		// normals
		for (let i = normalsArray.Lower(); i <= normalsArray.Upper(); i++) {
			const d = normalsArray.Value(i).Transformed(transformation);
			const index = (i - 1) * STRIDE;
			faceData.normals[index] = d.X();
			faceData.normals[index + 1] = d.Y();
			faceData.normals[index + 2] = d.Z();
		}

		// indices
		let trisCount = 0;
		const orientation = faceOrientation(oc, face);
		for (let nt = 1; nt <= nbTriangles; nt++) {
			const t = tri.Triangle(nt);
			let n1 = t.Value(1);
			let n2 = t.Value(2);
			const n3 = t.Value(3);
			if (orientation == FaceOrientation.BACKWARD) {
				const tmp = n1;
				n1 = n2;
				n2 = tmp;
			}
			const index = trisCount * STRIDE;
			faceData.indices[index] = n1 - 1 + index0;
			faceData.indices[index + 1] = n2 - 1 + index0;
			faceData.indices[index + 2] = n3 - 1 + index0;
			trisCount++;
		}
		return faceData;
	});
}