From 3a13f2476ddf0edce301506a1ba821cd4942c402 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E2=80=9CIsaac?= <isaac@isaacmason.com>
Date: Mon, 15 Aug 2022 20:01:42 +1000
Subject: [PATCH] Use connected faces from generated convex hull

Motivation:
- Generated convex hulls did not have connected faces, which is required for convex-convex collision in cannon-es
- Using the connected faces generated by ConvexHull addresses this
- Fixes #76
---
 lib/ConvexHull.d.ts |  1 +
 lib/ConvexHull.js   | 55 +++++++++++++++++++++++++++++++++++++++++----
 src/index.ts        | 41 +++++++++++++--------------------
 3 files changed, 67 insertions(+), 30 deletions(-)

diff --git a/lib/ConvexHull.d.ts b/lib/ConvexHull.d.ts
index f2521d2..b342ec2 100644
--- a/lib/ConvexHull.d.ts
+++ b/lib/ConvexHull.d.ts
@@ -13,4 +13,5 @@ declare class Face {
 declare class ConvexHull {
     public faces: Face[];
     setFromObject(mesh: Mesh): this;
+    collectFacesAndVertices(): { faces: number[][]; vertices: Vector3[]; }
 }
diff --git a/lib/ConvexHull.js b/lib/ConvexHull.js
index fe37696..9ed1be6 100644
--- a/lib/ConvexHull.js
+++ b/lib/ConvexHull.js
@@ -1,5 +1,4 @@
 import {
-	BufferGeometry,
 	Line3,
 	Plane,
 	Triangle,
@@ -42,6 +41,41 @@ var ConvexHull = ( function () {
 
 	Object.assign( ConvexHull.prototype, {
 
+		collectFacesAndVertices: function () {
+			// Get face vertex indices.
+			// These indices reference the array positions of all input vertices, which include vertices inside the convex hull.
+			// These will be re-mapped to the convex hull's vertices, which exclude interior vertices.
+			const faceIndices = this.faces.map((f) => f.collectIndices());
+
+			// Get distinct vertex indices referenced by convex hull faces, in ascending order.
+			const referencedFaceIndices = Array.from(new Set(faceIndices.flat())).sort();
+
+			// Create a mapping between the original vertex indices to new vertex indices,
+			// excluding vertex indices that are not part of the generated convex hull.
+			const originalToNewIndex = new Map();
+			for (let i = 0; i < referencedFaceIndices.length; i++) {
+				originalToNewIndex.set(referencedFaceIndices[i], i);
+			}
+
+			// Get faces with remapped vertex indices.
+			const faces = [];
+			for (let i = 0; i < faceIndices.length; i++) {
+				const indices = faceIndices[i];
+				const a = originalToNewIndex.get(indices[0]);
+				const b = originalToNewIndex.get(indices[1]);
+				const c = originalToNewIndex.get(indices[2]);
+				faces.push([a, b, c]);
+			}
+
+			// Get vertices referenced by faces.
+			const vertices = [];
+			for (let i = 0; i < referencedFaceIndices.length; i++) {
+				vertices.push(this.vertices[referencedFaceIndices[i]].point);
+			}
+
+			return { faces, vertices };
+		},
+
 		setFromPoints: function ( points ) {
 
 			if ( Array.isArray( points ) !== true ) {
@@ -60,7 +94,7 @@ var ConvexHull = ( function () {
 
 			for ( var i = 0, l = points.length; i < l; i ++ ) {
 
-				this.vertices.push( new VertexNode( points[ i ] ) );
+				this.vertices.push( new VertexNode( points[ i ], i ) );
 
 			}
 
@@ -980,6 +1014,16 @@ var ConvexHull = ( function () {
 
 	Object.assign( Face.prototype, {
 
+		collectIndices: function () {
+			const indices = [];
+			let edge = this.edge;
+			do {
+				indices.push(edge.head().index);
+				edge = edge.next;
+			} while (edge !== this.edge);
+			return indices;
+		},
+
 		getEdge: function ( i ) {
 
 			var edge = this.edge;
@@ -1105,12 +1149,15 @@ var ConvexHull = ( function () {
 
 	// A vertex as a double linked list node.
 
-	function VertexNode( point ) {
+	function VertexNode( point, index ) {
 
 		this.point = point;
+		// index in the input array
+		this.index = index;
 		this.prev = null;
 		this.next = null;
-		this.face = null; // the face that is able to see this vertex
+		// the face that is able to see this vertex
+		this.face = null;
 
 	}
 
diff --git a/src/index.ts b/src/index.ts
index 8527579..e8c4b0e 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,6 +1,6 @@
-import { Box, Quaternion as CQuaternion, ConvexPolyhedron, Cylinder, Shape, Sphere, Trimesh, Vec3 } from 'cannon-es';
+import { Box, ConvexPolyhedron, Cylinder, Quaternion as CQuaternion, Shape, Sphere, Trimesh, Vec3 } from 'cannon-es';
 import { Box3, BufferGeometry, CylinderGeometry, MathUtils, Mesh, Object3D, SphereGeometry, Vector3 } from 'three';
-import { ConvexHull } from '../lib/ConvexHull.js';
+import { ConvexHull } from '../lib/ConvexHull';
 import { getComponent, getGeometry, getVertices } from './utils';
 
 const PI_2 = Math.PI / 2;
@@ -254,34 +254,23 @@ function getConvexPolyhedronParameters (object: Object3D): ShapeParameters<Shape
 		);
 	}
 
-	// Compute the 3D convex hull.
-	const hull = new ConvexHull().setFromObject(new Mesh(geometry));
-	const hullFaces = hull.faces;
-	const vertices: number[] = [];
-	const faces: number[][] = [];
-
-	let currentFaceVertex = 0;
-	for (let i = 0; i < hullFaces.length; i++) {
-		const hullFace = hullFaces[ i ];
-		const face: number[] = [];
-		faces.push(face);
-
-		let edge = hullFace.edge;
-		do {
-			const point = edge.head().point;
-			vertices.push(point.x, point.y, point.z);
-			face.push(currentFaceVertex);
-			currentFaceVertex++;
-			edge = edge.next;
-		} while ( edge !== hullFace.edge );
+	// Compute the 3D convex hull and collect convex hull vertices and faces.
+	const { vertices: verticesArray, faces } = new ConvexHull()
+		.setFromObject(new Mesh(geometry))
+		.collectFacesAndVertices();
+
+	const vertices = new Float32Array(verticesArray.length * 3);
+	for (let i = 0; i < verticesArray.length; i++) {
+		const { x, y, z } = verticesArray[i];
+		const v = i * 3;
+		vertices[v] = x;
+		vertices[v + 1] = y;
+		vertices[v + 2] = z;
 	}
 
-	const verticesTypedArray = new Float32Array(vertices.length);
-	verticesTypedArray.set(vertices);
-
 	return {
 		type: ShapeType.HULL,
-		params: { vertices: verticesTypedArray, faces },
+		params: { vertices, faces },
 	};
 }