From f5f4fe7259cb8aeec36cad45e2bc342eda3f109f Mon Sep 17 00:00:00 2001
From: Passive <20432486+PassiveModding@users.noreply.github.com>
Date: Thu, 31 Jul 2025 23:07:22 +1000
Subject: [PATCH] Invalid tangent fix example

---
 Penumbra/Import/Models/Export/MeshExporter.cs | 45 ++++++++++++++++---
 1 file changed, 40 insertions(+), 5 deletions(-)

diff --git a/Penumbra/Import/Models/Export/MeshExporter.cs b/Penumbra/Import/Models/Export/MeshExporter.cs
index 0070a808..11c84677 100644
--- a/Penumbra/Import/Models/Export/MeshExporter.cs
+++ b/Penumbra/Import/Models/Export/MeshExporter.cs
@@ -340,6 +340,39 @@ public class MeshExporter
 
         return typeof(VertexPositionNormalTangent);
     }
+    
+    private const float UnitLengthThresholdVec3 = 0.00674f;
+    internal static bool _IsFinite(float value)
+    {
+        return float.IsFinite(value);
+    }
+    
+    internal static bool _IsFinite(Vector2 v)
+    {
+        return _IsFinite(v.X) && _IsFinite(v.Y);
+    }
+
+    internal static bool _IsFinite(Vector3 v)
+    {
+        return _IsFinite(v.X) && _IsFinite(v.Y) && _IsFinite(v.Z);
+    }
+    internal static Boolean IsNormalized(Vector3 normal)
+    {
+        if (!_IsFinite(normal)) return false;
+
+        return Math.Abs(normal.Length() - 1) <= UnitLengthThresholdVec3;
+    }
+    internal static Vector3 SanitizeNormal(Vector3 normal)
+    {
+        if (normal == Vector3.Zero) return Vector3.UnitX;
+        return IsNormalized(normal) ? normal : Vector3.Normalize(normal);
+    }
+    internal static Vector4 SanitizeTangent(Vector4 tangent)
+    {
+        var n = SanitizeNormal(new Vector3(tangent.X, tangent.Y, tangent.Z));
+        var s = float.IsNaN(tangent.W) ? 1 : tangent.W;
+        return new Vector4(n, s > 0 ? 1 : -1);
+    }
 
     /// <summary> Build a geometry vertex from a vertex's attributes. </summary>
     private IVertexGeometry BuildVertexGeometry(IReadOnlyDictionary<MdlFile.VertexUsage, List<object>> attributes)
@@ -352,19 +385,21 @@ public class MeshExporter
         if (_geometryType == typeof(VertexPositionNormal))
             return new VertexPositionNormal(
                 ToVector3(GetFirstSafe(attributes, MdlFile.VertexUsage.Position)),
-                ToVector3(GetFirstSafe(attributes, MdlFile.VertexUsage.Normal))
+                SanitizeNormal(ToVector3(GetFirstSafe(attributes, MdlFile.VertexUsage.Normal)))
             );
 
         if (_geometryType == typeof(VertexPositionNormalTangent))
         {
             // (Bi)tangents are universally stored as ByteFloat4, which uses 0..1 to represent the full -1..1 range.
             // TODO: While this assumption is safe, it would be sensible to actually check.
-            var bitangent = ToVector4(GetFirstSafe(attributes, MdlFile.VertexUsage.Tangent1)) * 2 - Vector4.One;
-
+            // var bitangent = ToVector4(GetFirstSafe(attributes, MdlFile.VertexUsage.Tangent1)) * 2 - Vector4.One;
+            var vec4      = ToVector4(GetFirstSafe(attributes, MdlFile.VertexUsage.Tangent1));
+            var bitangent = vec4 with { W = vec4.W == 1 ? 1 : -1 };
+            
             return new VertexPositionNormalTangent(
                 ToVector3(GetFirstSafe(attributes, MdlFile.VertexUsage.Position)),
-                ToVector3(GetFirstSafe(attributes, MdlFile.VertexUsage.Normal)),
-                bitangent
+                SanitizeNormal(ToVector3(GetFirstSafe(attributes, MdlFile.VertexUsage.Normal))),
+                SanitizeTangent(bitangent)
             );
         }