From 58a7e9243d1f13d826d225deb17753cd653bf1c8 Mon Sep 17 00:00:00 2001
From: Adam Johnson <AdamJohnso@gmail.com>
Date: Sun, 29 Aug 2021 21:56:42 -0400
Subject: [PATCH] Fix regression in negative object scaling.

---
 korman/exporter/mesh.py    |  2 +-
 korman/exporter/physics.py |  6 +++---
 korman/exporter/utils.py   | 11 +++++++++++
 3 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/korman/exporter/mesh.py b/korman/exporter/mesh.py
index 8187854..a064870 100644
--- a/korman/exporter/mesh.py
+++ b/korman/exporter/mesh.py
@@ -604,7 +604,7 @@ class MeshConverter(_MeshManager):
         else:
             mesh = bo.to_mesh(bpy.context.scene, True, "RENDER", calc_tessface=False)
             with helpers.TemporaryObject(mesh, bpy.data.meshes.remove):
-                mesh.transform(bo.matrix_world)
+                utils.transform_mesh(mesh, bo.matrix_world)
                 return self._export_mesh(bo, mesh)
 
     def _export_mesh(self, bo, mesh):
diff --git a/korman/exporter/physics.py b/korman/exporter/physics.py
index e93bc06..c0303aa 100644
--- a/korman/exporter/physics.py
+++ b/korman/exporter/physics.py
@@ -78,7 +78,7 @@ class PhysicsConverter:
                     vertices = [hsVector3(i.co.x * scale.x, i.co.y * scale.y, i.co.z * scale.z) for i in mesh.vertices]
             else:
                 # apply the transform to the physical itself
-                mesh.transform(mat)
+                utils.transform_mesh(mesh, mat)
                 mesh.update(calc_tessface=indices)
                 vertices = [hsVector3(*i.co) for i in mesh.vertices]
 
@@ -102,7 +102,7 @@ class PhysicsConverter:
             mesh = bo.to_mesh(bpy.context.scene, True, "RENDER", calc_tessface=False)
             with TemporaryObject(mesh, bpy.data.meshes.remove):
                 # No mass and no emedded xform, so we force worldspace collision.
-                mesh.transform(bo.matrix_world)
+                utils.transform_mesh(mesh, bo.matrix_world)
                 mesh.update(calc_tessface=True)
 
                 if z_coord is None:
@@ -283,7 +283,7 @@ class PhysicsConverter:
                 physical.rot = utils.quaternion(mat.to_quaternion())
                 bmesh.ops.scale(mesh, vec=mat.to_scale(), verts=mesh.verts)
             else:
-                mesh.transform(mat)
+                utils.transform_mesh(mesh, mat)
 
             result = bmesh.ops.convex_hull(mesh, input=mesh.verts, use_existing_faces=False)
             BMVert = bmesh.types.BMVert
diff --git a/korman/exporter/utils.py b/korman/exporter/utils.py
index cdae5b7..a29a052 100644
--- a/korman/exporter/utils.py
+++ b/korman/exporter/utils.py
@@ -15,6 +15,7 @@
 
 import bmesh
 import bpy
+import mathutils
 
 from typing import Callable, Iterator, Tuple
 from contextlib import contextmanager
@@ -110,3 +111,13 @@ def temporary_mesh_object(source : bpy.types.Object) -> bpy.types.Object:
         yield obj
     finally:
         bpy.data.objects.remove(obj)
+
+def transform_mesh(mesh: bpy.types.Mesh, matrix: mathutils.Matrix):
+    # There is a disparity in terms of how negative scaling is displayed in Blender versus how it is
+    # applied (Ctrl+A) in that the normals are different. Even though negative scaling is evil, we
+    # prefer to match the visual behavior, not the non-intuitive apply behavior. So, we'll need to
+    # flip the normals if the scaling is negative. The Blender documentation even "helpfully" warns
+    # us about this.
+    mesh.transform(matrix)
+    if matrix.is_negative:
+        mesh.flip_normals()