Grease Pencil Outline Modifier not showing with duplicated camera in outliner #102375

System Information
Operating system: Windows-10-10.0.19045-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 3060 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 522.33

Blender Version
Broken: version: 3.4.0 Alpha, branch: master, commit date: 2022-10-19 10:48, hash: f0fba1a2d8
Worked: (newest version of Blender that worked as expected)

Short description of error
The outline modifier of a grease pencil is not showing with a camera that gots duplicated in the outliner

Exact steps for others to reproduce the error
[Please describe the exact steps needed to reproduce the issue]
[Based on the default startup or an attached .blend file (as simple as possible)]

Remove the default cube
In the outliner copy and paste the default camera
Remove the first camera
Add a grease pencil stroke
Add a Outline modifier to it

The outline will not show.

This bug is related to this report. I am just not sure if it is two different causes and cases, or the same. https://developer.blender.org/T102373

2022-11-09 10-30-57.mp4

Added subscriber: @tiles

After realizing what the cause is: This issue is indeed the same issue than in the other task. You need a active camera for this modifier to function. And when you remove the active camera here, then the other is not active. And so the modifier stops working.

Added subscribers: @antoniov, @PratikPB2123

Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'

Hi, thanks for the report. I see we need active camera for outline modifier to work. but shouldn't it work if we manually set "duplicated" camera as active.
As far as I understood from quick testing, outline modifier only detects active camera if we re-add the modifier or toggle viewport visibility option of object/modifier
I'm not sure whether this is expected. @antoniov ?

Changed status from 'Needs Developer To Reproduce' to: 'Confirmed'

I have checked and the problem is the scene miss the camera when you delete the first one.

Before:

After:

As the scene camera is empty, the modifier cannot determine what is the camera to use.

@PratikPB2123 I can try to inform in the modifier, but do you think this is correct in the Outliner when you delete the camera that the scene gets NULL as camera? maybe it's correct just is double check if we could improve it or it's logic as today.

Added subscriber: @mendio

@mendio What do you think to add a warning in the top of the modifer. I cannot put in red because this would need a deep change in the modifiers code because I haven't the required data to check the scene camera and now this change is not logic with the futture plans we have.

@mendio I could do this...but not sure it's the way to go.

but do you think this is correct in the Outliner when you delete the camera that the scene gets NULL as camera?

Yes, the current behavior make sense to me.

As the scene camera is empty, the modifier cannot determine what is the camera to use.

Totally agree with it
My point is: if we manually set the duplicated camera as active then outliner modifier doesn't detect the camera
How to reproduce:

Repeat all steps mentioned in the report as it is (or just open the attached file)
set the duplicated camera as active in scene properties tab (outline modifier won't work. Will work if we do this )
#102375.blend

I personally find a warning a great improvement already.

Just wanted to add, doesn't the Line Art Modifier have the same problem? It is also dependant of a active camera from what i know. And there is the Outline tool in edit mode. Not a modifier, but also requires a active camera.

Or maybe this:

@tiles Yes, maybe LineArt has the same issue. Not tested yet.

Tested LineArt. It works in some cases because it uses a different approach, but the result is a bit strange. You do get a result, but not the one you might expect.

Added subscriber: @pablovazquez

After talking with more members of the team, we think this is the best design that follows Blender UI.

Waiting for the opinion of @pablovazquez

@antoniov, I agree with you about showing a warning message in modifiers panel. But question I raised was bit different. Did you check my last comment?

@PratikPB2123

My point is: if we manually set the duplicated camera as active then outliner modifier doesn't detect the camera

I think the problem is when you set the new camera to the scene, it looks we miss some update. As soon you update moving the frame, it's fixed... do you know how we could fix this? I don't want to add a refresh too aggressive to scene camera prop.

Warning message added in commit cad11f3098

Still pending the refresh issue.

Set as Known Issue because the main problem was fixed.

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Grease Pencil Outline Modifier not showing with duplicated camera in outliner #102375