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

Francesc Juhe fjuhec at gmail.com
Wed Oct 21 19:35:56 CEST 2015

On 21 Oct 2015, at 16:32, Alexander Romanov <a.romanov at blend4web.com> wrote:

> There is a problem of backward compatibility. You need to think 
> carefully and not to break existing Addons if you want to remove custom 
> trees from bpy.data.node_groups. In any case, it will be a low-level 
> pointer. As I understand internal nodes are stored in specified 
> datablocks such as Material, Scene... And they are ina hard hierarchical 
> relationship. Internal nodetree depends onits parent datablock. You can 
> choose this parent datablock from a collection like bpy.data.Materials, 
> but can't reuse its nodetree by some another datablock. In the case of a 
> custom nodetree it is useful to have a possibility to reuse a nodetree. 
> So, maybe it would be more accurate to have access to custom nodetrees 
> from, say, bpy.data.custom_node_trees, but it works fine now for 
> bpy.data.node_groups.

Yes, you are right about compatibility and reusability of node_groups in the current format. Ok, don’t think more about it.
Being able to link to data with a proper IDPointerProperty is the way to go.

>> 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.
> I think, it would looks like:
> class MyNodeTree(bpy.types.NodeTree):
>     bl_idname ='MyNodeTree'
>     bl_source_types = {"OBJECT", "WORLD", "MATERIAL”}

I was thinking on a function like the one accepted by EnumProperty that returned items (sequence of string tuples or a function) – sequence of enum items formatted: [(identifier, name, description, icon, number), …] 
I think it would be more versatile for custom node trees.

>> - 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.
> if you start before melet me know, please. Iwill also informyou.
>> In the Mitsuba Addon I am reusing SpaceNodeEditor.shader_type to select between world and object data source and works ok.

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