How to randomly rotate each object with this Geometry Node tree?

Question

I would like to create a geometry node tree that randomly rotates every object it is added to. This will let me create, say, one brick, and make each duplicate procedurally rotated slightly differently while still placing them manually.

In other words: for every object, a random value is generated (I don't know if this would use ID or index or something else; I'm not good with Geometry Nodes). This can be fed into some sort of transform node to rotate each object's geometry differently within the node tree.

How can I accomplish this?

Answer 1

Update:

you can use this node setup:

unfortunately you have to give each object another value so that it is random.

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you could use this node setup:

Just add your objects to that collection.

Answer 2

Here's the simplest way I could solve it.

It's not true, full randomization since you need one external object to act as seed and it is location-dependent so they keep rotating if you move them (if two objects are in the same world-position, their rotations are also the same) but it's a quick set-up and would work in many cases (like stationary bricks). The whole point of the seed object is to get a world-coordinate info into the node tree, which I couldn't figure out how to do without an external object but I'm no expert so it might be redundant if there's a simpler method to get stable unique ids per object I'm not aware of.

One other note: the "precision value" here exaggerates the distance between the input object and the seed, so the higher the number, more seed-changes while moving the object. I tried exposing this number in the Group Input as well, but as soon as I do that we lose randomization per object and all copies get the same seed, no matter if it's exposed as a Vector input or Float. I don't know why this happens and I'd appreciate any insight.

Min and Max random rotations are exposed in the Group Input so you can independently control them for each object. Here, active object's rotation is limited to the Z axis.

Answer 3

You can add an integer input to your node setup, and add a driver to it in the modifier stack: fmod(hash(name), 10e7).

Then the geo setup:

Then you can duplicate your cube:

❌ The biggest problem with this solution is that it requires enabling Script Auto-execution, which introduces security risks and makes it harder to share work with others. See my answer to another question, where I elaborate.

According to bpy_driver.c in Blender source, there's really no way to convert a string into a somewhat unique number. If not for a 256 character limit of driver expressions, you could use a script like that:

from bpy import context as C
import string

chars = string.ascii_letters + string.digits
significant_characters = 20
base = len(chars)

expr = ""
for i in range(significant_characters):
    for j, c in enumerate(chars):
        if i or j:
            expr += "+"
        expr += f"{base**i+j}*(n[{i}]=='{c}')"
        
C.active_object.animation_data.drivers[0].driver.expression = expr

✅ But to lighten things up, there are some important advantages of this approach: the rotation is decoupled from position. And object can move without rotating if you want it to. An object following another object won't mimic the rotation of the one in front from a moment ago.