Modifier's persistent_uid are not correctly assigned when appending or opening objects prior 4.2 #125952

New Issue

Julio Cargnin Pereira · 2024-08-06T10:39:04+02:00

2024-08-06 10:39:04 +02:00

System Information
Operating system: Linux-6.9.3-76060903-generic-x86_64-with-glibc2.35 64 Bits, X11 UI
Graphics card: NVIDIA GeForce RTX 4090/PCIe/SSE2 NVIDIA Corporation 4.6.0 NVIDIA 555.58.02

Blender Version
Broken: version: 4.2.1 Release Candidate, branch: blender-v4.2-release, commit date: 2024-08-05 13:24, hash: 174f8de75e63
Worked: (newest version of Blender that worked as expected)

Short description of error
Blender 4.2 can't assign modifier's persistent_uids when opening or appending objects created in earlier versions of Blender.

Exact steps for others to reproduce the error

Assign couple modifiers to the default cube in Blender 3.6 LTS, for example.
Save the file.
In 4.2, append the object.
Print the unique IDs with the script:

import bpy

# Function to print all modifiers and their unique IDs
def print_modifiers(obj):
    for mod in obj.modifiers:
        print(f"Modifier: {mod.name}, Unique ID: {mod.persistent_uid}")

# Example usage
obj = bpy.context.active_object
print_modifiers(obj)

Notice their unique IDs are not random neither unique but just follow a linear increasing index.

Video for full contextualization:

Kind regards,
Cosmo.

**System Information** Operating system: Linux-6.9.3-76060903-generic-x86_64-with-glibc2.35 64 Bits, X11 UI Graphics card: NVIDIA GeForce RTX 4090/PCIe/SSE2 NVIDIA Corporation 4.6.0 NVIDIA 555.58.02 **Blender Version** Broken: version: 4.2.1 Release Candidate, branch: blender-v4.2-release, commit date: 2024-08-05 13:24, hash: `174f8de75e63` Worked: (newest version of Blender that worked as expected) **Short description of error** Blender 4.2 can't assign modifier's persistent_uids when opening or appending objects created in earlier versions of Blender. **Exact steps for others to reproduce the error** 1. Assign couple modifiers to the default cube in Blender 3.6 LTS, for example. 2. Save the file. 3. In 4.2, append the object. 4. Print the unique IDs with the script: ``` import bpy # Function to print all modifiers and their unique IDs def print_modifiers(obj): for mod in obj.modifiers: print(f"Modifier: {mod.name}, Unique ID: {mod.persistent_uid}") # Example usage obj = bpy.context.active_object print_modifiers(obj) ``` 5. Notice their unique IDs are not random neither unique but just follow a linear increasing index. Video for full contextualization: <video src="/attachments/6cf20751-69df-44eb-be0c-55f423ad995d" title="persistent_uid.mp4" controls></video> Kind regards, Cosmo.

persistent_uid.mp4

4.5 MiB

Julio Cargnin Pereira added the

labels 2024-08-06 10:39:05 +02:00

Iliya Katushenock commented

2024-08-06 15:24:05 +02:00

UID is a hash, it can be just 0,1,2... enumeration, but this also can be int_max, so you should not depend on the value of this UID, but use this only as a hash.

Julio Cargnin Pereira commented

2024-08-06 16:31:28 +02:00

UID is a hash, it can be just 0,1,2... enumeration, but this also can be int_max, so you should not depend on the value of this UID, but use this only as a hash.

Ok, so in other words these persistent_uid was not meant to store unique-random-integer-hash per modifier?

You're saying that we gonna have multiple same uids in different objects at the same time so... it dos not have the usability potential that I initially thought it would have?

> UID is a hash, it can be just 0,1,2... enumeration, but this also can be int_max, so you should not depend on the value of this UID, but use this only as a hash. Ok, so in other words these persistent_uid was not meant to store unique-random-integer-hash per modifier? You're saying that we gonna have multiple same uids in different objects at the same time so... it dos not have the usability potential that I initially thought it would have?

Iliya Katushenock commented

2024-08-06 16:33:59 +02:00

You're saying that we gonna have multiple same uids in different objects at the same time so

I do not see any duplication of the uid at the report, ony that they are doned in different way.

> You're saying that we gonna have multiple same uids in different objects at the same time so I do not see any duplication of the uid at the report, ony that they are doned in different way.

Julio Cargnin Pereira commented

2024-08-06 17:23:54 +02:00

You're saying that we gonna have multiple same uids in different objects at the same time so

I do not see any duplication of the uid at the report, ony that they are doned in different way.

I've tried myself in 4.2 deleting the latest modifier and then adding it back. It is assigned with the same hash. (shouldn't be a different new integer?).

Also if you duplicate a existing object with modifiers, the hashes are going to remain the same in the other object.

I assumed Blender would assign unique ones when the duplication happens too, but I probably miss interpreting how this persistent_uid is created and what could be its usability.

I assumed this would be a random number per modifier but it seems this is not the case.

> > You're saying that we gonna have multiple same uids in different objects at the same time so > > I do not see any duplication of the uid at the report, ony that they are doned in different way. I've tried myself in 4.2 deleting the latest modifier and then adding it back. It is assigned with the same hash. (shouldn't be a different new integer?). Also if you duplicate a existing object with modifiers, the hashes are going to remain the same in the other object. I assumed Blender would assign unique ones when the duplication happens too, but I probably miss interpreting how this persistent_uid is created and what could be its usability. I assumed this would be a random number per modifier but it seems this is not the case.

Iliya Katushenock added the

   if (!MAIN_VERSION_FILE_ATLEAST(bmain, 401, 20)) {
     LISTBASE_FOREACH (Object *, ob, &bmain->objects) {
       int uid = 1;
       LISTBASE_FOREACH (ModifierData *, md, &ob->modifiers) {
         /* These identifiers are not necessarily stable for linked data. If the linked data has a
          * new modifier inserted, the identifiers of other modifiers can change. */
         md->persistent_uid = uid++;
       }
     }
   }

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Modifier's persistent_uid are not correctly assigned when appending or opening objects prior 4.2 #125952