Expression for Additive Transform Noise

Question

May I reference the current property's value before an expression in an expression? This driver expression will generate random values between -1 and 1: 2.0 * (noise.random() - 0.5)

If I was to add that to the current location.x, for example, it seems like it would be: self.location[0] + 2.0 * (noise.random() - 0.5)

This however would keep adding to the location.x value on every frame rather than adding to the original value (before the expression). I'm used to After Effects expressions that use value for this.

Thank you!

A simulation zone approach is also possible: https://blender.stackexchange.com/a/294231/60486 — Markus von Broady, Sep 06 '23 at 22:04

score 3 · Accepted Answer · answered Sep 06 '23 at 09:37

3

I don't know if there is a way to cache variables within a driver natively, but if not you can add a custom function to the driver namespace which handles that. Run this script to install the function and just call it in the driver.

import bpy
from mathutils import noise
def relative_noise():
    obj = bpy.data.objects['Cube']
if bpy.context.scene.frame_current == 0:
    # cache initial value at the desired frame
    relative_noise.locationx = obj.location.x
else:
    # make noise relative to initial position
    obj.location.x = relative_noise.locationx + 2.0 * (noise.random() - 0.5)

return obj.location.x


relative_noise.locationx = 0  # avoid a global
add function to the driver namespace
bpy.app.driver_namespace['relative_noise'] = relative_noise

You can now place the object freely and it will wobble around that position.

answered Sep 06 '23 at 09:37

taiyo

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when blender is closed and file reopened, is this saved or do we need to run the script again? – Harry McKenzie Sep 06 '23 at 10:57
@HarryMcKenzie afaik the script must be re-run. Re-opening Blender gives immediately a NameError: name 'relative_noise' is not defined (in the driver) in the console. Dunno how this can be improved (and would love to see, also a shorter way for caching values than mine). – taiyo Sep 06 '23 at 11:15
1

oh u dont need to run it. u can just Register the script and it will run automatically when u open the blend file like here https://blender.stackexchange.com/a/299887/142292 – Harry McKenzie Sep 06 '23 at 11:47
1

Awesome, i didn't know! Is this registration tied to the blend file? – taiyo Sep 06 '23 at 12:08
1

yes only tied to this blend file – Harry McKenzie Sep 06 '23 at 12:09
1

Aaah, perfection :) – taiyo Sep 06 '23 at 12:20
That works and I've learned so much from this post. Thank you!!!! – Dr. Pontchartrain Sep 06 '23 at 13:06

Expression for Additive Transform Noise

1 Answers1

add function to the driver namespace