PyNodes opens up the node system in Blender to scripters and adds a number of UI-level improvements.
=== Dynamic node type registration ===
Node types can now be added at runtime, using the RNA registration mechanism from python. This enables addons such as render engines to create a complete user interface with nodes.
Examples of how such nodes can be defined can be found in my personal wiki docs atm [1] and as a script template in release/scripts/templates_py/custom_nodes.py [2].
=== Node group improvements ===
Each node editor now has a tree history of edited node groups, which allows opening and editing nested node groups. The node editor also supports pinning now, so that different spaces can be used to edit different node groups simultaneously. For more ramblings and rationale see (really old) blog post on code.blender.org [3].
The interface of node groups has been overhauled. Sockets of a node group are no longer displayed in columns on either side, but instead special input/output nodes are used to mirror group sockets inside a node tree. This solves the problem of long node lines in groups and allows more adaptable node layout. Internal sockets can be exposed from a group by either connecting to the extension sockets in input/output nodes (shown as empty circle) or by adding sockets from the node property bar in the "Interface" panel. Further details such as the socket name can also be changed there.
[1] http://wiki.blender.org/index.php/User:Phonybone/Python_Nodes
[2] http://projects.blender.org/scm/viewvc.php/trunk/blender/release/scripts/templates_py/custom_nodes.py?view=markup&root=bf-blender
[3] http://code.blender.org/index.php/2012/01/improving-node-group-interface-editing/
The node_add_move operator is an extended variant which starts the (modal) transform operator right after adding a node, as a quicker way of inserting nodes in a tree.
The 'Add' menu in the node editor now has an option 'Search' at the top, which opens a separate popup for searching node types by name.
The operator for this is implemented completely in Python (this could also be done for the regular menu-based Add options in the future). There are a few necessary extensions to the RNA as well:
* The View2D struct in regions is now exposed. Currently only contains converter functions for coordinates from the region to the view (i.e. scrolled and zoomed view space). Used for converting mouse location to node space.
* The SpaceNode exposes the existing 'cursor_location' for operators to store mouse position beyond invoke calls. Not used for anything else (transforms) so far.
* The edit_tree in SpaceNode is also exposed, this is needed for operators to work correctly inside node groups.
