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2.8 Grease pencil. 'Pen up' event seems delayed relative to pen movement.
Open, Needs Triage by DeveloperPublic

Description

System Information
Operating system: MacOS 10.14
Graphics card: Radeon Pro 580 8192 MB
Wacom Cintiq 27QHDT drawing tablet. Drivers up to date.

Blender Version
Broken: blender-2.80.0 2019-04-17 5d8030b8f3cf x86_64

Short description of error
Since using grease pencil (all 2.8 versions i tried) when I'm using the Grab and Push sculpt tools with my drawing tablet the following often happens:

  1. In a swift movement I push some vertexes in my drawing, lift the pen from the tablet, and move the pen away from the drawing area to get a better look at the change i've made.
  2. But the last vertexes i moved end up being pushed away from where I wanted them, in the direction I moved my pen away from the gesture. This inconvenience gets more noticeable and more of a nuisance as my drawings get more dense and lagginess increases.

It's as if the 'pen up' event from my tablet ends up further back in the event queue than it's supposed to be, relative to the 'pen move' data. And so Blender acts as if my 'pen up' happened later than it really did, and pushes the points again without me wanting them moved.

(I'm pretty sure this isn't a case of my inadertently moving the pen away before releasing the press. I've been drawing on tablets for decades in other software and never had a similar issue.)

To reproduce:

  1. Open attached file.
  2. Use a wacom tablet with the grease pencil 'grab' tool to move parts of the leftmost vertical line around, using swift strokes.

Details

Type
Bug

Event Timeline

I can reproduce it (win7, GT640, yesturday build)
It looks so: I move line slow, then up pen and move it aside fast. But Blender still counts pressure. The same with mouse but little less.
Feels like presure/click input lag without moving input lag, so moving is overtaking clicks.