Fix T96294: Crash and error with shape key normal calculation

A mistake in the mesh normal refactor caused the wrong mesh to
be used when calculating normals with a shape key's deformation.

This commit fixes the normal calculation by using the correct mesh,
with just adjusted vertex positions, and calculating the results
directly into the result arrays when possible. This completely avoids
the need to make a local copy of the mesh, which makes sense,
since the only thing that changes is the vertex positions.

Differential Revision: https://developer.blender.org/D14317

1 files changed, 15 insertions, 0 deletions

diff --git a/source/blender/blenkernel/BKE_mesh.h b/source/blender/blenkernel/BKE_mesh.h
index 2373bb289cd..0ba9713b96d 100644
--- a/source/blender/blenkernel/BKE_mesh.h
+++ b/source/blender/blenkernel/BKE_mesh.h
@@ -472,6 +472,21 @@ void BKE_mesh_calc_normals_poly(const struct MVert *mvert,
                                 float (*r_poly_normals)[3]);
 
 /**
+ * Calculate face and vertex normals directly into result arrays.
+ *
+ * \note Usually #BKE_mesh_vertex_normals_ensure is the preferred way to access vertex normals,
+ * since they may already be calculated and cached on the mesh.
+ */
+void BKE_mesh_calc_normals_poly_and_vertex(const struct MVert *mvert,
+                                           int mvert_len,
+                                           const struct MLoop *mloop,
+                                           int mloop_len,
+                                           const struct MPoly *mpoly,
+                                           int mpoly_len,
+                                           float (*r_poly_normals)[3],
+                                           float (*r_vert_normals)[3]);
+
+/**
  * Calculate vertex and face normals, storing the result in custom data layers on the mesh.
  *
  * \note It is usually preferable to calculate normals lazily with