Fix inherited 3MF triangle property group resolution

app/Services/ThreeMfGeometryExtractor.php

@@ -561,7 +561,7 @@ class ThreeMfGeometryExtractor
         $ancestry[] = $objectId;
 
         if ($object['mesh'] !== null) {
-            $defaultColor = $this->resolveColor($baseMaterials, $object['pid'], $object['pindex']);
+            $this->resolveColor($baseMaterials, $object['pid'], $object['pindex']);
             $determinant = $transform[0] * ($transform[4] * $transform[8] - $transform[5] * $transform[7])
                 - $transform[1] * ($transform[3] * $transform[8] - $transform[5] * $transform[6])
                 + $transform[2] * ($transform[3] * $transform[7] - $transform[4] * $transform[6]);
@@ -578,9 +578,11 @@ class ThreeMfGeometryExtractor
                     throw new RuntimeException('3MF triangle references a vertex index that does not exist.');
                 }
 
-                $color = $triangle['pid'] !== null
-                    ? $this->resolveColor($baseMaterials, $triangle['pid'], $this->resolveTriangleVertexIndex($triangle))
-                    : $defaultColor;
+                $color = $this->resolveColor(
+                    $baseMaterials,
+                    $triangle['pid'] ?? $object['pid'],
+                    $this->resolveTriangleVertexIndex($triangle, $object['pindex']),
+                );
 
                 $triangles[] = [
                     'v' => [
@@ -640,13 +642,14 @@ class ThreeMfGeometryExtractor
      * the face. This renderer only paints one flat colour per triangle, so a
      * triangle that actually declares differing per-vertex indices is
      * rejected explicitly rather than silently picking p1 and discarding the
-     * rest of the declared colour data.
+     * rest of the declared colour data. The property group and first index
+     * inherit independently from object pid and pindex; omitted p2/p3 use p1.
      *
      * @param  array{v1:int,v2:int,v3:int,pid:?int,p1:?int,p2:?int,p3:?int}  $triangle
      */
-    private function resolveTriangleVertexIndex(array $triangle): ?int
+    private function resolveTriangleVertexIndex(array $triangle, ?int $objectPindex): ?int
     {
-        $p1 = $triangle['p1'];
+        $p1 = $triangle['p1'] ?? $objectPindex;
         $p2 = $triangle['p2'] ?? $p1;
         $p3 = $triangle['p3'] ?? $p1;