[Bf-committers] Link custom node trees to datablocks.

Francesc Juhe fjuhec at gmail.com
Wed Oct 21 12:46:39 CEST 2015

Sure, PointerProperty would be a great addition to the API but seems like a complicated issue.
If it could accept filters then it can be used as a substitute for prop_search.

Something like:
  bpy.props.IDProperty(type=‘OBJECT’, subtype=‘CAMERA') # to link a camera an object

  bpy.props.IDProperty(src=bpy.data.objects, filter=some_python_filter_func) # to link an ID from bpy.data.objects with filter

In the end, I would be happy with the PointerProperty and being able to link to objects, node_groups or whatever.

I proposed the NodeTree property just to be on par with internal node trees, they are not stored in bpy.data.node_groups, they are stored on the ID. But sure, a PointerProperty would work for solving issue (2) you mention.

As for issue, (1) Generalized nodetree editing, I think this could work:

- Add a property to SpaceNodeEditor to hold the custom nodetree type.
- Add a function registered on NodeTreeType that returns a list of accepted data sources.
- Add appropriate draw code on space_node.py to draw the data source icons provided by the function and storing it on the SpaceNodeEditor property.
- NodeTreeType then uses the property to know the data source selected on the Node Editor.

I wanted to try to make a patch for this but haven’t had the time yet, I think this issue is not as difficult as the other.

In the Mitsuba Addon I am reusing SpaceNodeEditor.shader_type to select between world and object data source and works ok.

On 21 Oct 2015, at 10:34, Alexander Romanov <a.romanov at blend4web.com> wrote:

> Hi!
> Not sure about another storage for nodetrees. I think, there should be 
> one storage for them and multiple storages for links.
> But I agreewith Isaac about generalization. Here is some discussion 
> about PointerProperty https://developer.blender.org/T34766 . I think, 
> this is the way to go. And that is what I also was thinking about. There 
> are two separate issues : 1) Generalized nodetree editing through 
> Blender UI for a nodetree linked to any datablock. 
> (http://wiki.blender.org/index.php/Linking_Custom_Node_Tree_to_DataBlock) 2) 
> Make it possible to create links of any types with reference counting 
> through python PointerProperty. (https://developer.blender.org/T34766) 
> What do you think about PointerProperty?
> On 21.10.2015 04:40, Isaac Weaver wrote:
>> I like the idea of adding a new property type, but I wonder if it could be
>> generalized to more ID types (Object, Scene, etc.)
>> Maybe something like this:
>>     bpy.props.IDProperty(subtype='OBJECT') # to store an object
>>     bpy.props.IDProperty(subtype='SCENE') # to store a scene
>>     bpy.props.IDProperty(subtype='NODE_TREE', type=NodeTreeType) # to store
>> a node tree
>> Would a property like this make sense?
>> Thanks,
>> ~ Isaac
>> On Tue, Oct 20, 2015 at 1:58 PM, Francesc Juhe <fjuhec at gmail.com> wrote:
>>> Hello,
>>> As the main developer behind the Mitsuba exporter I like your proposal.
>>> It would greatly improve the current workflow.
>>> But I would also like to make another proposal.
>>> - Add to Blender a bpy.props.NodeTree(type=NodeTreeType) that can be
>>> attached to ID. This way there is no need to fill the bpy.data.node_groups.
>>> - Add a function to NodeTreeType that can be called from blender or python
>>> and returns a list of accepted data sources by that NodeTreeType. That way
>>> the node editor can show the appropriate options to the user to select the
>>> correct data source.
>>> What do you think? Possible?
>>> Cheers,
>>> Francesc
>>> On 07 Oct 2015, at 16:32, Alexander Romanov <a.romanov at blend4web.com>
>>> wrote:
>>>> Hello everyone from Blend4Web Team!
>>>> We're currently working with node trees in our node-based logic editor
>>>> and we've noticed some
>>>> shortcomings in python API. We have some ideas about improving API for
>>>> custom node trees.
>>>> Briefly, we want to make it possible to link custom node trees to
>>>> datablocks such as Scene,
>>>> Object, etc. Here is a link to the proposal:
>>>> http://wiki.blender.org/index.php/Linking_Custom_Node_Tree_to_DataBlock
>>>> I would like to discuss this with developers of addons which use custom
>>>> node trees, such as Sverchok and Luxrender.
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> -- 
> Alexander Romanov (Blend4Web Team)
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