Blender Git Loki

EditMesh: Avoid creating deform-vert layer every redraw

Getting a new edit-derived-bmesh was always creating a deform-vert array, even when it wasn't needed.
Since this was called on redraw, in many cases it was doing it unnecessarily.

Now pass in a custom-data mask and only fill in deform-verts when needed.

Gives noticeable drawing speedup (~10-30% here).