Mesh: Tag normals dirty instead of calculating

Because mesh vertex and face normals are just derived data, they can
be calculated lazily instead of eagerly. Often normal calculation is
a relatively expensive task, and the calculation is often redundant
if the mesh is deformed afterwards anyway.

Instead, normals should be calculated only when they are needed. This
commit moves in that direction by adding a new function to tag a mesh's
normals dirty and replacing normal calculation with it in some places.

Differential Revision: https://developer.blender.org/D12107

1 files changed, 6 insertions, 0 deletions

diff --git a/source/blender/blenkernel/intern/mesh_normals.cc b/source/blender/blenkernel/intern/mesh_normals.cc
index f496d6eada1..8740baa5aef 100644
--- a/source/blender/blenkernel/intern/mesh_normals.cc
+++ b/source/blender/blenkernel/intern/mesh_normals.cc
@@ -63,6 +63,12 @@ static CLG_LogRef LOG = {"bke.mesh_normals"};
 /** \name Mesh Normal Calculation
  * \{ */
 
+void BKE_mesh_normals_tag_dirty(Mesh *mesh)
+{
+  mesh->runtime.cd_dirty_vert |= CD_MASK_NORMAL;
+  mesh->runtime.cd_dirty_poly |= CD_MASK_NORMAL;
+}
+
 /**
  * Call when there are no polygons.
  */