Subdivision: add support for vertex creasing

This adds vertex creasing support for OpenSubDiv for modeling, rendering,
Alembic and USD I/O.

For modeling, vertex creasing follows the edge creasing implementation with an
operator accessible through the Vertex menu in Edit Mode, and some parameter in
the properties panel. The option in the Subsurf and Multires to use edge
creasing also affects vertex creasing.

The vertex crease data is stored as a CustomData layer, unlike edge creases
which for now are stored in `MEdge`, but will in the future also be moved to
a `CustomData` layer. See comments for details on the difference in behavior
for the `CD_CREASE` layer between egdes and vertices.

For Cycles this adds sockets on the Mesh node to hold data about which vertices
are creased (one socket for the indices, one for the weigths).

Viewport rendering of vertex creasing reuses the same color scheme as for edges
and creased vertices are drawn bigger than uncreased vertices.

For Alembic and USD, vertex crease support follows the edge crease
implementation, they are always read, but only exported if a `Subsurf` modifier
is present on the Mesh.

Reviewed By: brecht, fclem, sergey, sybren, campbellbarton

Differential Revision: https://developer.blender.org/D10145

2 files changed, 5 insertions, 0 deletions

diff --git a/release/scripts/startup/bl_ui/properties_data_mesh.py b/release/scripts/startup/bl_ui/properties_data_mesh.py
index ba5ecd1efde..49f196640d8 100644
--- a/release/scripts/startup/bl_ui/properties_data_mesh.py
+++ b/release/scripts/startup/bl_ui/properties_data_mesh.py
@@ -557,6 +557,7 @@ class DATA_PT_customdata(MeshButtonsPanel, Panel):
         col.enabled = obj is not None and obj.mode != 'EDIT'
         col.prop(me, "use_customdata_vertex_bevel", text="Vertex Bevel Weight")
         col.prop(me, "use_customdata_edge_bevel", text="Edge Bevel Weight")
+        col.prop(me, "use_customdata_vertex_crease", text="Vertex Crease")
         col.prop(me, "use_customdata_edge_crease", text="Edge Crease")
 
 
diff --git a/release/scripts/startup/bl_ui/space_view3d.py b/release/scripts/startup/bl_ui/space_view3d.py
index 11e272fddde..5eca606216e 100644
--- a/release/scripts/startup/bl_ui/space_view3d.py
+++ b/release/scripts/startup/bl_ui/space_view3d.py
@@ -4026,6 +4026,10 @@ class VIEW3D_MT_edit_mesh_vertices(Menu):
 
         layout.separator()
 
+        layout.operator("transform.vert_crease")
+
+        layout.separator()
+
         layout.operator("mesh.blend_from_shape")
         layout.operator("mesh.shape_propagate_to_all", text="Propagate to Shapes")