fix issue where probuilder with quad topology instead of triangle would trigger out of bounds exception when being exported (#619)

* fix issue where probuilder with quad topology instead of triangle would trigger out of bounds exception when being exported

* added changelog

* fix following PR comments

Author: varinotmUnity

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - [PBLD-242] Fixed a bug where edges were being incorrectly selected when one or both vertices were behind the camera's near plane, causing flipped lines and inconsistent selection behavior.
 - [PBLD-226] Fixed a bug where ProBuilder faces could not selected when obscured by another GameObject
 - [PBLD-164] Fixed a bug with UV autostitching where the position offset would not take into account the face rotation center offset.
+- [PBLD-251] Fixed a bug which would cause out of bounds exceptions when exporting meshes with quad topology
 - [PBLD-253] Removes call to internal API that is being removed.
 
 ## [6.0.6] - 2025-07-01

Runtime/Core/ProBuilderMeshFunction.cs

@@ -409,27 +409,37 @@ public void ToMesh(MeshTopology preferredTopology = MeshTopology.Triangles)
                 // remove any indices that contain degenerate triangles
                 int numBadIndices = 0;
                 int[] indexes = submeshes[i].m_Indexes;
-                for (var tri = 0; tri < indexes.Length; tri += 3)
+
+                if (submeshes[i].m_Topology == MeshTopology.Triangles && indexes.Length % 3 == 0)
                 {
-                    Vector3 ab = positions[indexes[tri + 1]] - positions[indexes[tri]];
-                    Vector3 ac = positions[indexes[tri + 2]] - positions[indexes[tri]];
-                    if (Vector3.Cross(ab, ac).sqrMagnitude < Mathf.Epsilon)
-                    {
-                        numBadIndices += 3;
-                    }
-                    else
+                    for (var tri = 0; tri < indexes.Length; tri += 3)
                     {
-                        submeshes[i].m_Indexes[tri - numBadIndices] = submeshes[i].m_Indexes[tri];
-                        submeshes[i].m_Indexes[tri - numBadIndices + 1] = submeshes[i].m_Indexes[tri + 1];
-                        submeshes[i].m_Indexes[tri - numBadIndices + 2] = submeshes[i].m_Indexes[tri + 2];
+                        if (tri + 2 >= indexes.Length ||
+                            indexes[tri] >= positions.Count ||
+                            indexes[tri + 1] >= positions.Count ||
+                            indexes[tri + 2] >= positions.Count)
+                            continue;
+
+                        Vector3 ab = positions[indexes[tri + 1]] - positions[indexes[tri]];
+                        Vector3 ac = positions[indexes[tri + 2]] - positions[indexes[tri]];
+                        if (Vector3.Cross(ab, ac).sqrMagnitude < Mathf.Epsilon)
+                        {
+                            numBadIndices += 3;
+                        }
+                        else
+                        {
+                            indexes[tri - numBadIndices] = indexes[tri];
+                            indexes[tri - numBadIndices + 1] = indexes[tri + 1];
+                            indexes[tri - numBadIndices + 2] = indexes[tri + 2];
+                        }
                     }
                 }
 
                 int[] fixedIndices;
                 if (numBadIndices > 0)
                 {
-                    fixedIndices = new int[submeshes[i].m_Indexes.Length - numBadIndices];
-                    submeshes[i].m_Indexes.AsSpan(0, fixedIndices.Length).CopyTo(fixedIndices);
+                    fixedIndices = new int[indexes.Length - numBadIndices];
+                    Array.Copy(indexes, 0, fixedIndices, 0, fixedIndices.Length);
                 }
                 else
                 {

Tests/Editor/Geometry/ProbuilderMeshDegenerateTriangleTest.cs

@@ -7,42 +7,57 @@
 
 public class ProbuilderMeshDegenerateTriangleTest
 {
-    private ProBuilderMesh m_Mesh;
-
-    [SetUp]
-    public void SetUp()
+    [Test]
+    public void TestNormalsWithDegenerateTriangles()
     {
         // Create a Probuilder cube
-        m_Mesh = ShapeFactory.Instantiate(typeof(Cube));
-    }
+        var mesh = ShapeFactory.Instantiate(typeof(Cube));
+        try
+        {
+            // Collapse two of the shared vertices together.
+            var positions = new List<Vector3>(mesh.positions);
+            Vector3 svPosition = positions[mesh.sharedVertices[0][0]];
+            for (int v = 0; v < mesh.sharedVertices[1].Count; ++v)
+            {
+                positions[mesh.sharedVertices[1][v]] = svPosition;
+            }
 
-    [TearDown]
-    public void TearDown()
-    {
-        // Clean up the created GameObject
-        GameObject.DestroyImmediate(m_Mesh.gameObject);
+            mesh.positions = positions.ToList();
+            mesh.Rebuild();
+
+            // Check all the normals in use by faces to ensure none have invalid values.
+            foreach (int index in mesh.mesh.triangles)
+            {
+                var normal = mesh.normals[index];
+                Assert.IsFalse(float.IsNaN(normal.x) || float.IsNaN(normal.y) || float.IsNaN(normal.z), "Normals should not contain NaN values.");
+                Assert.IsFalse(float.IsInfinity(normal.x) || float.IsInfinity(normal.y) || float.IsInfinity(normal.z), "Normals should not contain Infinite values.");
+                Assert.IsFalse(normal == Vector3.zero, "Normals should not be zero vectors.");
+            }
+        }
+        finally
+        {
+            // Clean up the created GameObject
+            GameObject.DestroyImmediate(mesh.gameObject);
+        }
     }
 
     [Test]
-    public void TestNormalsWithDegenerateTriangles()
+    [Description("PBLD-251 : IndexOutOfRangeException appears in the Console when exporting certain ProBuilder meshes")]
+    public void TestOriginalDoorBugScenario()
     {
-        // Collapse two of the shared vertices together.
-        var positions = new List<Vector3>(m_Mesh.positions);
-        Vector3 svPosition = positions[m_Mesh.sharedVertices[0][0]];
-        for (int v = 0; v < m_Mesh.sharedVertices[1].Count; ++v)
+        // Recreate the specific Door shape bug scenario
+        var door = ShapeFactory.Instantiate(typeof(Door));
+
+        try
         {
-            positions[m_Mesh.sharedVertices[1][v]] = svPosition;
-        }
-        m_Mesh.positions = positions.ToList();
-        m_Mesh.Rebuild();
+            Assert.DoesNotThrow(() => door.ToMesh(MeshTopology.Quads));
 
-        // Check all the normals in use by faces to ensure none have invalid values.
-        foreach (int index in m_Mesh.mesh.triangles)
+            Assert.IsNotNull(door.mesh);
+            Assert.Greater(door.mesh.vertexCount, 0);
+        }
+        finally
         {
-            var normal = m_Mesh.normals[index];
-            Assert.IsFalse(float.IsNaN(normal.x) || float.IsNaN(normal.y) || float.IsNaN(normal.z), "Normals should not contain NaN values.");
-            Assert.IsFalse(float.IsInfinity(normal.x) || float.IsInfinity(normal.y) || float.IsInfinity(normal.z), "Normals should not contain Infinite values.");
-            Assert.IsFalse(normal == Vector3.zero, "Normals should not be zero vectors.");
+            GameObject.DestroyImmediate(door.gameObject);
         }
     }
 }