[Bf-committers] Python Access to some properties of nodes

[Lukas Tönne]

IMHO storing the links in a separate list like we do now is one of the
more well-designed code parts ;)

It may be slightly inconvenient if you want to get a list of links for
a specific socket, but it has several advantages over storing lists of
links in each socket or node:

* If each socket stores its own link list that means a lot more
overhead for all those lists. Now we have exactly 1 list.
* You only ever need a single loop. If each socket has a list of
links, to walk over all links in a node tree (e.g. for drawing or the
cut operator) you need to walk over all nodes and then all sockets and
then all links ...
* Storing a link in sockets is ambiguous, you could store the link
either in the output or input socket. If you store it on one side only
you have to loop over everything again to find links of the other
side. If you store it in both you have to keep them in sync, which is
error prone and leads to redundant data.
* In terms of time complexity having to filter the list of all links
vs. a reduced list of socket links does not make much difference, both
are essentially O(N+M), where N is number of nodes, M is number of
links. In general though the node DNA should not be judged by
performance criteria too much, if you need to access the node
structure millions of times (e.g. in rendering) you should create an
optimized structure with arrays instead of linked lists and can store
links in whatever way is needed for fast access. All modern node
systems in Blender (cycles, compositor) do this.

Bottom line: the single links list is the best all-round solution for
the purpose of storing data in .blend files and user manipulation.

On Sat, Dec 22, 2012 at 2:49 AM, Dan Eicher <dan at trollwerks.org> wrote:
> On Fri, Dec 21, 2012 at 4:52 AM, Lukas Tönne <lukas.toenne at gmail.com> wrote:
>
>> # List of connected (Node, NodeSocket) pairs for 'socket':
>> input_sockets = [(link.from_node, link.from_socket) for link in
>> socket.id_data.links if link.to_socket == socket]
>> output_sockets = [(link.to_node, link.to_socket) for link in
>> socket.id_data.links if link.from_socket == socket]
>>
>
> Somewhat off topic...
>
> Looking at this code I'm starting to think that maybe it was a mistake to
> expose Node.links instead of having it as a property on the sockets
> themselves, it would make the code a lot clearer and it isn't like you can
> really do anything with the links independent of the sockets they're
> assigned to.
>
> It may even be better to totally abstract away the NodeLinks too, maybe
> socket.links just return a list of (Node, NodeSocket) tuples -- have to
> think on this a bit more though since it would probably require
> sub-classing NodeSocket into NodeInputSocket, NodeOutputSocket so you'd
> know if the returned node/socket pair was an input or output for the node.
>
> Would also clean up node.links.new(add?) a bunch.
>
> Dan
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