Basically, the problem we have detected is the mouse/pen events are missing when you move the mouse very fast. We have checked all the events in wm_event_add_mousemove() function and if you move very fast, you get only a fraction of the mouse positions. We have tested in Linux and Windows and the problem is mainly in Windows.
This is not a problem specific to 2.8x, it’s a general problem in all versions.
In the image above, I tried to draw a curve very fast with the mouse (artists draw these curves very fast to get gesture drawing)… as you can see, the distance increases when the mouse moved fast (in the curve section). Of course, we tested MOUSEMOVE and INBETWEEN_MOUSEMOVE events, but the problem is we never received an INBETWEEN_MOUSEMOVE event. The tested operator is using OPTYPE_BLOCKING flag.
For other tools to have all events is a nightmare, but for drawing in grease pencil this is critical. We have added a lot of tricks to smooth and try to simulate the missing events and we get a reasonable result, but the “real” solution is to get the events because any method used always “change” slightly the artist gesture.
@Daniel Martinez Lara (pepeland) was testing and Linux hasn’t this problem or is less noticeable, and the “feeling” is better in that OS.