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Maniphest T94860

Grease Pencil Grab sculpt tool causing line drift when tablet pen is held down in place
Closed, ResolvedPublicKNOWN ISSUE
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Description

System Information
Operating system: Win10
Graphics card: RTX3070

Blender Version
Broken: 3.0
Worked: n/a

Short description of error

Exact steps for others to reproduce the error

Open this file

GPMovesWhenHoldingDownTabletPenInSculpt.blend2 MBDownload

(I cannot reproduce this on a vanilla GP; I copied and emptied a GP object from my work project.)

Use a drawing tablet and hold your pen down to sculpt the strokes using the Grab tool, but don't move your pen. The strokes will all start drifting to the left.

This only happens with the Grab tool, and only when using a tablet pen; holding down Left Mouse with an actual mouse does not produce this bug.

I use an Xp-Pen Deco 03. Bug was also reproduced by other tablet users, using a Wacom Cintiq and an Xp-Pen Deco 01.

Video for further explanation:

https://youtu.be/C7ax-jshDSo

Revisions and Commits

rB Blender
D13870rB824f514f8f63 Fix T94860: GPencil - Avoid drift in Sculpt when mouse/pen is not moved

Related Objects

Event Timeline

Matthew Gafford (AFoxInSpace) created this task.Jan 12 2022, 11:13 PM
Richard Antalik (ISS) added subscribers: Antonio Vazquez (antoniov), Richard Antalik (ISS).Jan 18 2022, 7:35 PM

@Matthew Gafford (AFoxInSpace) Can you clarify what you mean by vanilla GP? I understand it as this is simplified .blend file with only problematic object.

I don't have tablet here, @Antonio Vazquez (antoniov) Can you reproduce?

Antonio Vazquez (antoniov) changed the task status from Needs Triage to Confirmed.Jan 18 2022, 7:42 PM
Antonio Vazquez (antoniov) changed the subtype of this task from "Report" to "Known Issue".

I can reproduce it with the Wacom tablet, but I'm not sure if we can consider this as a bug. The grab tool is receiving events and there is a small precision error that changes the stroke. I could try to find a way to avoid that, but we're talking about a very small offset due to the precision of the pen tablet sending small changes.

Now, IMHO we must set as know issue and investigate more in how driver is sending the position of the pen.

Antonio Vazquez (antoniov) mentioned this in D13870: GPencil: Avoid drift in Sculpt when mouse/pen is not moved.Jan 18 2022, 7:58 PM
Antonio Vazquez (antoniov) claimed this task.Jan 18 2022, 8:01 PM
Antonio Vazquez (antoniov) added a project: Grease Pencil.
Matthew Gafford (AFoxInSpace) added a comment.Jan 18 2022, 8:43 PM

I'd like to point out that the Push brush--which works very similarly to the Grab brush--does not have this problem. As a workaround I have switched over to the Push brush for now, but you might compare their code.

Antonio Vazquez (antoniov) added a comment.Jan 19 2022, 10:30 AM

My patch fixes these issues and really, it's something we had to do since the beginning because no point to do any action if the mouse has not moved. I did not look at the code details, but I'm 99% sure the problem was due an accumulation of math precision issues, but now with the patch this don't mind.

Antonio Vazquez (antoniov) closed this task as Resolved by committing rB824f514f8f63: Fix T94860: GPencil - Avoid drift in Sculpt when mouse/pen is not moved.Feb 12 2022, 10:51 AM
Antonio Vazquez (antoniov) added a commit: rB824f514f8f63: Fix T94860: GPencil - Avoid drift in Sculpt when mouse/pen is not moved.