Drive the viewport display color

theoryshaw · April 22

The following video shows how to 'drive' an object's viewport display color by its base color.
https://www.dropbox.com/scl/fi/ucdvh12ak1trpcipbmbcp/2024-04-22_06-56-25.mp4?rlkey=a3kseg8n8722rd7nmgzga99dy&dl=0

Is there a way, however, to 'drive' an object's viewport display color by the result color from a 'Combine Color' node, for example? Basically want to average all the colors of a texture, and apply that color to the viewport display color.

... but still have the texture viewable in 'Rendered' or 'Material Preview' mode.

stefanm2 · April 22

Hi, I've found that add-on.
https://www.blendernation.com/2020/03/06/free-addon-to-set-viewport-color-based-on-nodetree/

theoryshaw · April 22

cool!... will give it a spin.

theoryshaw · April 22

hmm... doesn't seem to work on my side (blender 4.1). It just sets the viewport display color to white.

stefanm2 · April 22

:-( sry

theoryshaw · April 22

@Gorgious provided some insight as well, here: https://blender.stackexchange.com/a/316981/97239

Andrej730 · April 23

@theoryshaw said:
hmm... doesn't seem to work on my side (blender 4.1). It just sets the viewport display color to white.

any errors?

Gorgious · April 24

Hey I'll expand a bit on my BSE answer and try and answer the concerns here.

What the addon does if I understood correctly is aggregate the default values of the color input of all the principled bsdfs of each material, and then set the viewport color accordingly. It does not work if you plug in a noodle coming from a texture node in the color input of the principled bsdf, so it will never work if you're using a PBR based workflow. The reason is because plugging in the noodle tells the node to ditch the default value and wait for the previous node to evaluate its output. For technical and optimization reasons this information is not available to the API. You can see the noodles as a pipeline, and you can only tweak the leftmost "default" values and you can only access the rightmost output from the material, and even then only if you bake the result to a texture. The Blender version won't change this fact, sorry.

The information is not statically available. You need to actively analyse the data from the texture map if you want to achieve your goal. I think the simplest way is as described in my answer, read the pixel colors and average them. This could be turned into an addon but I advise against running this script continuously, even if foreach_get is extremely fast, the information is not bound to change until the texture map itself changes so a button seems more reasonable.

import bpy
import numpy as np

img = bpy.data.images["Image.png"]  # Case sensitive
x, y = img.size
pixels = np.empty(x * y << 2, dtype=np.float32)
img.pixels.foreach_get(pixels)
mean_color_rgb = np.mean(pixels.reshape((x, y, 4))[:, :, :3], axis=(0, 1))  # Don't average alpha value

mat = bpy.data.materials["Material"]  # Case sensitive
mat.diffuse_color = list(mean_color_rgb) + [1]  # Add alpha value to the mean

Cheers

theoryshaw · April 24

Thanks @Gorgious !
Let's say you have a texture that is predominantly a red color, and you use a blue color in a 'color ramp' node.
Is there a clever way to set the viewport display color as the resultant purple color? It would seem not, from your explanation above, but wanted to ask just in case.

theoryshaw · April 25

I guess i should say something like a 'mix node', not a 'color ramp'--same concept though.
Something like the following example. Possible to get the average color at .5 factor, for example?

...

Gorgious · April 25

Everything is possible in Blender :) The only problem is how to tackle the issue. For very specific scenarii you'll need to write specific scripts. I omitted try/except and if/else clauses so this will throw error on other materials.

import bpy
import numpy as np


def get_mean_color(img):
    x, y = img.size
    pixels = np.empty(x * y << 2, dtype=np.float32)
    img.pixels.foreach_get(pixels)
    mean_color_rgb = np.mean(pixels.reshape((x, y, 4))[:, :, :3], axis=(0, 1))  # Don't average alpha value

    return mean_color_rgb


obj = bpy.context.active_object
mat = obj.data.materials[obj.active_material_index]

principled_bsdf = next(n for n in mat.node_tree.nodes if n.type == "BSDF_PRINCIPLED")
color_socket = principled_bsdf.inputs["Base Color"]
mix_node = color_socket.links[0].from_node
factor = mix_node.inputs["Factor"].default_value
texture_node_a = mix_node.inputs["A"].links[0].from_node
texture_node_b = mix_node.inputs["B"].links[0].from_node
image_a = texture_node_a.image
image_b = texture_node_b.image
image_a_mean_color = get_mean_color(image_a)
image_b_mean_color = get_mean_color(image_b)

mat.diffuse_color = [
    image_a_mean_color[0] * (1-factor) + image_b_mean_color[0] * factor,
    image_a_mean_color[1] * (1-factor) + image_b_mean_color[1] * factor,
    image_a_mean_color[2] * (1-factor) + image_b_mean_color[2] * factor,
    1
]

While I was writing this I noticed that the material icon in the material list updated when you changed the factor. There might be a way to tap into the material icon system to get the icon color. I unfortunately don't know much about it but that's a lead. I think the icons are dynamically re-rendered at very low resolution every time you change the material.