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is it possible to create custom nodes for the geometry node editor (NOT node groups, combining blender built-in nodes), define inputs and outputs and execute some python code in between? I couldn't find any information about completely userdefined nodes nor tutorials anywhere.

Further information about the usecase:

I want to create a node, which executes a more elaborate python code involving some linear algebra and finding eigenvalues of matrices. Therefore I created a python code using scipy, installed the scipy package in blender and I am already able to execute it within blender in the scripting environment and it outputs the correct values in the system console. Now I want to take the input values from a geometry node (position in x and y), calculate the output value of my python function and assign it as a z coordinate to all my verticies.

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    $\begingroup$ No, it's not possible. The developers have never exported an interface to python that would allow doing so and have routinely said that for performance reasons they would not. $\endgroup$
    – Marty Fouts
    Feb 28, 2022 at 21:12
  • $\begingroup$ ahhh, thats too bad. My problem is, that the operation is too complicated and can't be expressed as a combination of math nodes as far as I know. Due to the fact, that one input value of the matrix process has to be animated, I can't precompute the values in a different script and apply them as a displacement texture. $\endgroup$
    – Max Hacki
    Feb 28, 2022 at 21:25
  • $\begingroup$ instead of giving up or fixating on GN i would think about animation nodes or sverchok. There you can execute python code and use that result. And yes, you can combine animation nodes and geometry nodes. $\endgroup$
    – Chris
    Mar 1, 2022 at 6:58
  • $\begingroup$ Thanks Chris! I managed to use animation nodes(AN) and created my geometry inside AN, moved my verticies with some python code, thats it. perfect! thanks, I was not aware of AN. $\endgroup$
    – Max Hacki
    Mar 6, 2022 at 20:19
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    $\begingroup$ While there is no python API (and no plans to add one), the internal C++ API is fairly concise. I recommend this article on how to add your own geometry node: blog.exppad.com/article/writing-blender-geometry-node $\endgroup$
    – Fullk33
    Jun 15, 2022 at 8:14

1 Answer 1

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I've found this method:

import bpy
from bpy.types import Node, NodeSocket

class MyCustomNode(Node):
    '''This is a custom node that multiplies two inputs and outputs the result.'''

    bl_idname = 'CustomNodeType' # Unique identifier for your node type
    bl_label = 'My Custom Node' # Display name for your node

    # Define the input and output sockets for your node
    my_input_1 : NodeSocket
    my_input_2 : NodeSocket
    my_output : NodeSocket

    def init(self, context):
        # This method is called when the node is created
        self.inputs.new('NodeSocketFloat', 'Input 1')
        self.inputs.new('NodeSocketFloat', 'Input 2')
        self.outputs.new('NodeSocketFloat', 'Output')
    
    def update(self):
        # This method is called when the node updates
        self.outputs[0].default_value = self.inputs[0].default_value * self.inputs[1].default_value

# Register your node type with Blender
bpy.utils.register_class(MyCustomNode)

Simply execute the script, then add it to your nodes:

enter image description here

I was searching too, I'm just testing to go further...
Blender v3.4.1 - It's now possible -

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  • $\begingroup$ Hello ! Have you tested this ? It doesn't work. $\endgroup$
    – Gorgious
    May 9 at 15:36
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    $\begingroup$ Interesting approach, but unfortunately I have to confirm what @Gorgious noted: The node is visible, but the values are empty (tested with 3.4.x and 3.5.x). $\endgroup$
    – quellenform ♦
    May 9 at 16:00
  • $\begingroup$ Hi, yes that's what I said at the end of my post : "I'm just testing"... the node is created in the interface. It seems to be good to respect the connections types between nodes. Now I know nothing about the "update" function It's just a try, let's keep on going =) $\endgroup$
    – s4mdf0o1
    May 10 at 10:01
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    $\begingroup$ there are complications : projects.blender.org/blender/blender/issues/67649 PS: old posts, real situation to define... $\endgroup$
    – s4mdf0o1
    May 10 at 11:29
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    $\begingroup$ may be a way to do that gist.github.com/strike-digital/0b5a2c0111f1aec3923b5fd17d1881e2 lines 40, 218, then 248 $\endgroup$
    – s4mdf0o1
    May 11 at 6:38

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