Headless Sverchok

[JanFilipec]

Is it possible to execute sverchok scripts headlessly? I'd like to write a python script that takes user input, loads a sverchok tree based on the input, executes it and writes the output.

[Durman]

What you can do is to run Blender without GUI. I think something like this is possible:

1. Run Python
2. Run Blender in subprocess without GUI with custom script.
3. Custom script can import trees from json format, execute trees, record results in a file and finish the subprocess.
4. When subprcess has finished load results from the file.

Sverchok uses similar technic to perform some tests. It requires some knowlege about Sverchok internals.

[mifth]

Yeah, exactly like @Durman described.

One thing i would like to mention. After loading a node tree I had to update the node tree to get Sverchok's data.

I fixed it with: node_tree.process_ani(True, False). It will update all nodes immediately.

[portnov]

Script to run any script under Blender, run_sverchok_script.py — you run it with your system python:

#!/usr/bin/python3

# If your blender is not available as just "blender" command, then you need
# to specify path to blender when running this script, e.g.
#
# $ BLENDER=~/soft/blender-3.3.1/blender ./run_sverchok_script.py
#

import os
import sys
import argparse

BLENDER = os.environ.get('BLENDER', 'blender')

parser = argparse.ArgumentParser(description = "Run Python script which uses Sverchok API")
parser.add_argument('script', metavar="SCRIPT.PY", help = "Path to Python script file")
parser.add_argument('-b', '--blender', metavar="/PATH/TO/BLENDER", help = "Path to Blender executable", default = BLENDER)

argv = sys.argv[1:]
try:
    delimiter_idx = argv.index("--")
    my_arguments = argv[:delimiter_idx]
    script_arguments = argv[delimiter_idx+1:]
    script_args = " ".join(script_arguments)
except ValueError:
    my_arguments = argv
    script_args = ""

args = parser.parse_args(my_arguments)

command = f"{args.blender} -b --addons sverchok --python {args.script} --python-exit-code 1 -- {script_args}"
print(command)
os.system(command)

A simple script demonstrating usage of Sverchok API — bezier_example.py. You run it with ./run_sverchok_script.py [-b /path/to/blender] bezier_example.py

# We can import usual python modules here
import numpy as np

# Also we can import Sverchok API modules
from sverchok.utils.curve.bezier import SvBezierCurve

cpts = np.array([
            [-2.0, 0.0, 0.0],
            [-1.0, 1.0, 0.0],
            [1.0,  1.0, 0.0],
            [2.0,  1.0, 0.0]
        ])

curve = SvBezierCurve(cpts)
t_min, t_max = curve.get_u_bounds()
ts = np.linspace(t_min, t_max, num=50)
curve_points = curve.evaluate_array(ts)

print(curve_points)

This prints output to stdout.

A bit more complicated example — script_example.py, to be run as ./run_sverchok_script.py [-b /path/to/blender] script_example.py -- script_test_t1.blend:

# We can import usual python modules here
import sys
import numpy as np

# We can import Blender API
import bpy

# Also we can import Sverchok API modules
from sverchok.utils.testing import link_node_tree, get_node_tree

# Use only arguments which come after --
# ones which come earlier are intended for Blender itself, not for this script
argv = sys.argv
delimiter_idx = argv.index("--")
argv = argv[delimiter_idx+1:]

if len(argv) < 2:
    print("Usage: run_sverchok_script.py script_example.py -- FILE.blend TreeName")
    sys.exit(1)

blend_path = argv[0]
tree_name = argv[1]

# Load node tree. It will be processed upon loading.
link_node_tree(blend_path, tree_name)
tree = get_node_tree(tree_name)

out_buffer = bpy.data.texts['output.txt']
output = out_buffer.as_string()

with open('output.txt', 'wb') as f:
    f.write(output.encode('utf-8'))

This prints output to output.txt.

script_test_t1_2022_12_05_07_57.zip