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Maniphest T94116

Drivers can have multiple variables with same name
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Description

Currently, drivers can get several variables with the same exact name.

Besides being useless and confusing (typically, driver will only use the first one then), this is also a problem for library overrides, since there are several data (driver variables) with the same exact RNA path.

You can check e.g. lib/char/butterfly/butterfly.blend from sprite production files, GEO-butterfly_antennas object's drivers, burnt one has three burnt variables.

butterfly.blend4 MBDownload

LibOverride issue can be fixed by forbidding usage of names for the driver variables collection (only indices would be used then). However this has serious downsides, first one being that if a driver has several valid variables and they get re-arranged, the overrides will need to be resynced.

And in general I don't think such confusing useless situation should be allowed at all.

So think there should be a mechanism (maybe as part of driver_variable_name_validate ?) that should ensure unique names?

NOTE: found while investigating mysterious 'always need to resync overrides' cases from T94059.

Revisions and Commits

rB Blender
D13594rB4b21067aea41 Fix T94116: Drivers can have multiple variables with same name

Related Objects

Event Timeline

Bastien Montagne (mont29) changed the task status from Needs Triage to Confirmed.Dec 15 2021, 4:24 PM
Bastien Montagne (mont29) created this task.
Dalai Felinto (dfelinto) added a subscriber: Dalai Felinto (dfelinto).Dec 15 2021, 4:56 PM

For the records, in my tests here the drivers use the last variable, not the first one.

Bastien Montagne (mont29) added subscribers: Simon Thommes (simonthommes), Andy Goralczyk (eyecandy).Dec 15 2021, 5:03 PM

@Andy Goralczyk (eyecandy) @Simon Thommes (simonthommes) Also thing you need to know for now imho.

For the time being, this simple script allows to clean things up:

for _name in dir(bpy.data):
    iterable = getattr(bpy.data, _name)
    if not isinstance(iterable, bpy.data.objects.__class__):
        continue
    for id in iterable:
        if not getattr(id, "animation_data", None):
            continue
        for driver in id.animation_data.drivers:
            variable_names = set()
            for variable in driver.driver.variables:
                if variable.name in variable_names:
                    print("ERROR! ID driver '%s.%s' has several variables named '%s', removing the extra ones." % (id.name, driver.data_path, variable.name))
                    driver.driver.variables.remove(variable)
                else:
                    variable_names.add(variable.name)
Dalai Felinto (dfelinto) added a comment.EditedDec 15 2021, 6:06 PM

You actually need to traverse the list in the reverse order. Corrected script using reversed:

import bpy

for _name in dir(bpy.data):
    iterable = getattr(bpy.data, _name)
    if not isinstance(iterable, bpy.data.objects.__class__):
        continue
    for id in iterable:
        if not getattr(id, "animation_data", None):
            continue
        for driver in id.animation_data.drivers:
            variable_names = set()
            for variable in reversed(driver.driver.variables):
                if variable.name in variable_names:
                    print("ERROR! ID driver '%s.%s' has several variables named '%s', removing the extra ones." % (id.name, driver.data_path, variable.name))
                    driver.driver.variables.remove(variable)
                else:
                    variable_names.add(variable.name)

Sample file:

drivers-name-clash.blend102 KBDownload

Sybren A. Stüvel (sybren) claimed this task.Dec 16 2021, 12:09 PM

This is indeed something to address. There is no use for multiple variables when they all overwrite each other's value anyway.

So think there should be a mechanism (maybe as part of driver_variable_name_validate ?) that should ensure unique names?

I agree, but not in that function. That now has a clear, single purpose, and I don't want to add more things to it.

Sybren A. Stüvel (sybren) added a revision: D13594: Fix T94116: Drivers can have multiple variables with same name.Dec 16 2021, 12:55 PM
Sybren A. Stüvel (sybren) mentioned this in D13594: Fix T94116: Drivers can have multiple variables with same name.
Bastien Montagne (mont29) mentioned this in T94059: Library Override Resync Performance.Dec 16 2021, 5:32 PM
Bastien Montagne (mont29) moved this task from Backlog to Bugs on the Core board.Dec 17 2021, 12:31 PM
Bastien Montagne (mont29) moved this task from Bugs to Other Modules Responsibility on the Core board.
Sybren A. Stüvel (sybren) closed this task as Resolved by committing rB4b21067aea41: Fix T94116: Drivers can have multiple variables with same name.Dec 17 2021, 5:33 PM
Sybren A. Stüvel (sybren) added a commit: rB4b21067aea41: Fix T94116: Drivers can have multiple variables with same name.