Python Geometry Node Trees

Question

I'm trying to make a script that assigns a custom Geometry Node Tree to a bezier curve. The node tree contains 3 custom node groups. I have created the groups with code but I can't assign them to the Geometry Node Modifier/Root Tree. I basically want the script to create a bezier curve with the Geometry Nodes already assigned, how can I do that? Thanks!!

Answer 1

You need to access the node tree through the geometry nodes modifier. Here's the start of a script that would allow you to do that:

import bpy
from mathutils import Vector

bpy.ops.curve.primitive_bezier_curve_add()
bpy.ops.object.modifier_add(type='NODES')  

curve = bpy.context.active_object

def new_GeometryNodes_group():
    ''' Create a new empty node group that can be used
        in a GeometryNodes modifier.
    '''
    node_group = bpy.data.node_groups.new('GeometryNodes', 'GeometryNodeTree')
    inNode = node_group.nodes.new('NodeGroupInput')
    inNode.outputs.new('NodeSocketGeometry', 'Geometry')
    outNode = node_group.nodes.new('NodeGroupOutput')
    outNode.inputs.new('NodeSocketGeometry', 'Geometry')
    node_group.links.new(inNode.outputs['Geometry'], outNode.inputs['Geometry'])
    inNode.location = Vector((-1.5*inNode.width, 0))
    outNode.location = Vector((1.5*outNode.width, 0))
    return node_group

# In 3.2 Adding the modifier no longer automatically creates a node group.
# This test could be done with versioning, but this approach is more general
# in case a later version of Blender goes back to including a node group.
if curve.modifiers[-1].node_group:
    node_group = curve.modifiers[-1].node_group    
else:
    node_group = new_GeometryNodes_group()
    curve.modifiers[-1].node_group = node_group

nodes = node_group.nodes

Update: As per an edit by Gorgious, Blender 3.2 no longer creates a node tree when you add the modifier. I've updated that edit to handle both older versions of Blender and Blender 3.2

You still have to hook the Geometry output of the Group Input node to your first node and the Geometry output of your last node to the Geometry Input node of the Group Output node. Here's an example with a single node:

group_in = nodes.get('Group Input')
group_out = nodes.get('Group Output')

new_node = nodes.new('GeometryNodeMeshToPoints')

node_group.links.new(group_in.outputs['Geometry'], new_node.inputs['Mesh'])
node_group.links.new(new_node.outputs['Points'], group_out.inputs['Geometry'])

For Blender 3.6

import bpy
from mathutils import Vector

bpy.ops.curve.primitive_bezier_curve_add()
bpy.ops.object.modifier_add(type='NODES')  

curve = bpy.context.active_object

def new_GeometryNodes_group():
    ''' Create a new empty node group that can be used
        in a GeometryNodes modifier.
    '''
    node_group = bpy.data.node_groups.new('GeometryNodes', 'GeometryNodeTree')
    inNode = node_group.nodes.new('NodeGroupInput')
    node_group.outputs.new('NodeSocketGeometry', 'Geometry')
    outNode = node_group.nodes.new('NodeGroupOutput')
    node_group.inputs.new('NodeSocketGeometry', 'Geometry')
    node_group.links.new(inNode.outputs['Geometry'], outNode.inputs['Geometry'])
    inNode.location = Vector((-1.5*inNode.width, 0))
    outNode.location = Vector((1.5*outNode.width, 0))
    return node_group

# In 3.2 Adding the modifier no longer automatically creates a node group.
# This test could be done with versioning, but this approach is more general
# in case a later version of Blender goes back to including a node group.
if curve.modifiers[-1].node_group:
    node_group = curve.modifiers[-1].node_group    
else:
    node_group = new_GeometryNodes_group()
    curve.modifiers[-1].node_group = node_group

nodes = node_group.nodes

A list of node sockets can be added with reference to this document.

https://docs.blender.org/api/current/bpy.types.NodeSocketStandard.html