Custom Render Stamp, Principled BDSF values

Question

I am trying to do a material study, and I would like to print the Principled BDSF values onto the render.

Previously I had found this: How to show render-stamp for arbitrary values?

It had worked, but the data path I get when I right click the roughness parameter for the Principled BDSF is: nodes["Principled BSDF"].inputs[7].default_value

That doesn't seem to work the same way.

here is the script:

import bpy

def stamp_set(scene):
    note  =   "Samples: "                     + str(scene.cycles.samples)
    note += ", Bounces, Max: "                + str(scene.cycles.max_bounces)
    note += ", roughness: "                + str(nodes["Principled BSDF"].inputs[7].default_value)
    note += ", Version: "                     + bpy.app.version_string
    scene.render.stamp_note_text = note


bpy.app.handlers.render_pre.append(stamp_set)

I also tried, cycles.nodes["Principled BSDF"].inputs[7].default_value

and

scene.nodes["Principled BSDF"].inputs[7].default_value

I get an error in the terminal that these are undefined (I think).

SO, how would I go about doing this?

thanks,

eh five

Answer 1

I found a solution with various references. The big thing that helped was finding how to enter the value for a Principled BSDF parameter in the console;

bpy.data.materials['Material'].node_tree.nodes["Principled BSDF"].inputs[1].default_value = 3 

Mostly from here:

Change value of material emission strength from Python console or script

The final script looks like this (input 7 is Roughness):

import bpy

def stamp_set(scene):
    note  =   "Samples: "                     + str(scene.cycles.samples)
    note += ", Bounces, Max: "                + str(scene.cycles.max_bounces)
    note += ", Roughness: "                + str(round(bpy.data.materials['Material'].node_tree.nodes["Principled BSDF"].inputs[7].default_value, 3))
    note += ", Version: "                     + bpy.app.version_string
    scene.render.stamp_note_text = note


bpy.app.handlers.render_pre.append(stamp_set)

ref:

Editing Lamp Strength with Python

Change value of sun light emission strength from Python console or script

decreasing excess precision:

How to show render-stamp for arbitrary values?

-snaok