From ffe1ca05e8e3918d3fb58b9e1d9e3545a9a4b57c Mon Sep 17 00:00:00 2001
From: Stewart Allen <so@a3z.co>
Date: Tue, 17 Jan 2023 21:19:53 -0500
Subject: [PATCH] add support for obj extended face declaration

---
 src/geo/base.js |  5 ++++-
 src/load/obj.js | 17 +++++++++++++----
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/src/geo/base.js b/src/geo/base.js
index 4ce26fa8..6956ad9b 100644
--- a/src/geo/base.js
+++ b/src/geo/base.js
@@ -410,7 +410,7 @@ function orderClosest(array, fn, from) {
 // wrapper for earcut that handles higher order dimensions and finds the
 // two with the greatest delta to pass to the earcut algorith, then returns
 // an unwrapped array in the original dimensions
-function triangulate(array, holes, dims) {
+function triangulate(array, holes, dims, pos) {
     let narray;
     let info;
     if (dims === 2) {
@@ -452,6 +452,9 @@ function triangulate(array, holes, dims) {
         }
     }
     let ec = earcut(narray, holes, 2);
+    if (pos) {
+        return ec;
+    }
     let oa = new Array(ec.length * dims);
     for (let i = 0, e = 0, l = ec.length, ai; i < l; i++) {
         ai = ec[i] * dims;
diff --git a/src/load/obj.js b/src/load/obj.js
index cc3cfd30..a053efdf 100644
--- a/src/load/obj.js
+++ b/src/load/obj.js
@@ -44,10 +44,19 @@ function parse(text) {
                 break;
             case 'f':
                 let tok = toks.map(f => parseInt(f.split('/')[0]));
-                // add support for negative indices (offset from last vertex array point)
-                faces.appendAll(verts[tok[0]-1]);
-                faces.appendAll(verts[tok[1]-1]);
-                faces.appendAll(verts[tok[2]-1]);
+                if (tok.length > 3) {
+                    const p = tok.map(t => verts[t-1]).flat();
+                    const t = base.util.triangulate(p, [], 3, true);
+                    const r = t.map(i => tok[i]);
+                    for (let v of r) {
+                        faces.appendAll(verts[v - 1]);
+                    }
+                } else {
+                    // add support for negative indices (offset from last vertex array point)
+                    faces.appendAll(verts[tok[0]-1]);
+                    faces.appendAll(verts[tok[1]-1]);
+                    faces.appendAll(verts[tok[2]-1]);
+                }
                 break;
             case 'g':
                 if (faces.length) {