[Bf-codereview] Flexible modes for node grouping operators (issue 6303064)

[lukas.toenne at googlemail.com]

Reviewers: bf-codereview_blender.org,

Description:
Modification of node groups by adding/removing nodes is not possible
yet. This patch extends the 'Make Group' operator and adds a new
'Separate' operator to add such functionality.

1) For inserting into existing groups:
    The 'Make Group from selected' (CTRL+g) operator shows a selection
popup (like the object parenting operator), with options depending on
the type of the active node (last selected):
    * "New" -> regular operator, creates new group type with all selected
nodes inside.
    * "Insert" (only if active node is a group) -> adds all other
selected nodes into the group.
    Currently still prohibits groups inside groups in general, though
would be technically possible as long as no actual recursion occurs
(group containing itself).

2) For extracting from an existing group:
    New 'Separate from group' operator (p), works similar to separating
vertices/edges/faces from mesh. Two modes:
    * "Copy" makes a copy of the nodes in the parent tree, but keeps the
original group intact.
    * "Move" removes selected nodes from the node group and adds them to
the parent tree

See the bf-committers mailing list for a more detailed description and
rationale.

Please review this at http://codereview.appspot.com/6303064/

Affected files:
   source/blender/blenkernel/BKE_node.h
   source/blender/editors/space_node/node_edit.c
   source/blender/editors/space_node/node_intern.h
   source/blender/editors/space_node/node_ops.c
   source/blender/nodes/intern/node_common.c
   source/blender/nodes/intern/node_common.h