Pupil weird deform/translation along X

[Guillaume Taton]

Observed with both Blender 5.1.2 and Blender 4.5.2 on file 08-2D-eye-rig_START.blend(EYES_course-files_v1.2)…

I have almost zero knowledge about grease pencil but I noticed a weird behaviour of the Pupil layer of 2D_Eye grease pencil: it does not ‘deform’/translate properly according to its deforming bone along X axis.

I noticed that when testing the iris_follow driver on MCH-Pupil armature constraint (14:51 in the video)

So I tested with a single-bone armature, parented the GEO to the  armature with empty weights and assigned the pupil with 1.0 weight to the sole bone related vertex group
Same result. Exagerated in the screenshots yet still noticeable when moving the pupil ctrl bone near the edge of the eye along X (with iris_follow set to 0):

Since I also noticed the pupil was not rigorously circular (slightly squashed along X) while assigning the widget, I played with the transform properties of the Pupil layer (grease pencil object) and found that setting the Scale X to 1.059 seemed to fix both the shape of the pupil and the proportional offset with the deforming bone

I know I’m being a bit fussy there as that is not a blocking issue but it feels weird that the pupil (and only the pupil) would not fully follow its rig ctrl.
If anyone knows how to fix the grease pencil without messing with the layers props, I’d be glad to learn how it shall be fixed 😉

[Wayne Dixon]

That’s a bug with Grease Pencil, Guillaume.
I was hoping that no one discovered that, but I’m impressed that you did.
It tells me that you are really pulling things apart to figure out they work – this is a good thing.

As for the bug, I actually forgot about it and never reported it.
But it’s worth me digging in again when I have time to find the root cause – and/or experiment with actual cutouts that you can do  these days.

I have started coding in c++ to fix bugs and add features to Blender, but not in the Grease Pencil module (that is beyond my knowledge)

[Guillaume Taton]

Oh! Well if you, a seasoned Blender contributor, have already found it to be a Blender bug, then it explains why I couldn’t see any misfit prop in the UI for that piece of geometry…
When I have time, I’ll should check if it’s already been reported, otherwise I’d try and recreate the problem from an empty scene to report it, it would force me to learn a few things about grease pencil.
Thanks for the answer!

[Wayne Dixon]

Oh if you could find a way to replicate it in the most simple way that is extremely helpful.

The first thing I would try, is to delete everything except the pupil, iris and the bones that control them.
Then remove any GP layers that aren’t used anymore so it’s just what’s used.

If it’s still present, then you rebuild this thing from scratch (the simple version) and see if it happens in the latest version starting from nothing.
That’s when you know you’ve isolated the bug and it isn’t caused by anything weird in the older file.

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