MeshPainter: Rückseiten-Abweisung über Flächen-Normale bei großem Brush

Zusätzlich zum Kugel-Test wird die Oberflächen-Normale jedes Texels gegen
die Brush-Normale geprüft (CPU/GPU/Preview). Neues Inspector-Feld
"Brush Max Surface Angle" (90-180°, Default 120°). Bei fehlenden Mesh-Normalen
Degradation zur reinen Kugel.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Assets/Scripts/Components/MeshPainter/MeshPainter.Setup.cs

@@ -42,6 +42,7 @@ public partial class MeshPainter
     // BuildMeshCaches scratch: refilled per bake without allocating (with updateColliderEveryFrame this
     // runs per frame while painting; mesh.vertices/.triangles/.uv return fresh arrays per call).
     private readonly System.Collections.Generic.List<Vector3> _vertScratch = new System.Collections.Generic.List<Vector3>();
+    private readonly System.Collections.Generic.List<Vector3> _normalScratch = new System.Collections.Generic.List<Vector3>();
     private int _meshCacheId; // mesh instance the topology/UV caches were built for (0 = none)
 
     /// <summary>Reads vertices/triangles/UVs of the collider mesh and computes culling data.
@@ -56,6 +57,16 @@ public partial class MeshPainter
         if (_verts == null || _verts.Length != vCount) _verts = new Vector3[vCount];
         _vertScratch.CopyTo(_verts);
 
+        // Per-vertex normals for the brush's back-face rejection (opposite side of thin geometry).
+        // Re-baked each frame for skinned meshes; falls back to null (test disabled) if absent.
+        m.GetNormals(_normalScratch);
+        if (_normalScratch.Count == vCount)
+        {
+            if (_normals == null || _normals.Length != vCount) _normals = new Vector3[vCount];
+            _normalScratch.CopyTo(_normals);
+        }
+        else _normals = null;
+
         if (_meshCacheId != m.GetInstanceID())
         {
             _meshCacheId = m.GetInstanceID();