Implement additional modes for Shrinkwrap to a surface.

In addition to the original map to surface and Keep Above Surface,
add modes that only affect vertices that are inside or outside
the object. This is inspired by the Limit Distance constraint,
and can be useful for crude collision detection in rigs.

The inside/outside test works based on face normals and may not be
completely reliable near 90 degree or sharper angles in the target.

Reviewers: campbellbarton, mont29

Differential Revision: https://developer.blender.org/D3717

release/scripts/startup/bl_ui/properties_constraint.py

@@ -748,6 +748,9 @@ class ConstraintButtonsPanel:
         layout.prop(con, "distance")
         layout.prop(con, "shrinkwrap_type")
 
+        if con.shrinkwrap_type in {'PROJECT', 'NEAREST_SURFACE'}:
+            layout.prop(con, 'wrap_mode', text="Snap Mode")
+
         if con.shrinkwrap_type == 'PROJECT':
             row = layout.row(align=True)
             row.prop(con, "project_axis", expand=True)