Add 'Set From Faces' tool to custom split normals.

Feature request during bconf, makes sense to have it even as an hack for
now, since this is probably one of the most common use cases. This should
be redone in bmesh once we have proper custom noramls handling in edit mode...

release/scripts/startup/bl_operators/mesh.py

@@ -198,3 +198,53 @@ class MeshSelectPrev(Operator):
             bmesh.update_edit_mesh(me, False)
 
         return {'FINISHED'}
+
+
+# XXX This is hackish (going forth and back from Object mode...), to be redone once we have proper support of
+#     custom normals in BMesh/edit mode.
+class MehsSetNormalsFromFaces(Operator):
+    """Set the custom vertex normals from the selected faces ones"""
+    bl_idname = "mesh.set_normals_from_faces"
+    bl_label = "Set Normals From Faces"
+    bl_options = {'REGISTER', 'UNDO'}
+
+    @classmethod
+    def poll(cls, context):
+        return (context.mode == 'EDIT_MESH' and context.edit_object.data.polygons)
+
+    def execute(self, context):
+        import mathutils
+
+        bpy.ops.object.mode_set(mode='OBJECT')
+        obj = context.active_object
+        me = obj.data
+
+        v2nors = {}
+        for p in me.polygons:
+            if not p.select:
+                continue
+            for lidx, vidx in zip(p.loop_indices, p.vertices):
+                assert(me.loops[lidx].vertex_index == vidx)
+                v2nors.setdefault(vidx, []).append(p.normal)
+
+        for nors in v2nors.values():
+            nors[:] = [sum(nors, mathutils.Vector((0, 0, 0))).normalized()]
+
+        if not me.has_custom_normals:
+            me.create_normals_split()
+        me.calc_normals_split()
+
+        normals = []
+        for l in me.loops:
+            nor = v2nors.get(l.vertex_index, [None])[0]
+            if nor is None:
+                nor = l.normal
+            normals.append(nor.to_tuple())
+
+        me.normals_split_custom_set(normals)
+
+        me.free_normals_split()
+        bpy.ops.object.mode_set(mode='EDIT')
+
+        return {'FINISHED'}
+

release/scripts/startup/bl_ui/space_view3d_toolbar.py

@@ -431,6 +431,7 @@ class VIEW3D_PT_tools_shading(View3DPanel, Panel):
         col.label(text="Normals:")
         col.operator("mesh.normals_make_consistent", text="Recalculate")
         col.operator("mesh.flip_normals", text="Flip Direction")
+        col.operator("mesh.set_normals_from_faces", text="Set From Faces")
 
 
 class VIEW3D_PT_tools_uvs(View3DPanel, Panel):