Ending a stroke outside the canvas may cause a "shooting line"

[jigpu]

Description of the problem

While painting with a tablet, if a stroke ends outside the canvas it seems that MyPaint may render a line that shoots from the end of the stroke towards point the pen re-enters the canvas (even though the pen is up at this point). If the pen is held down outside of the canvas while in this state and then dragged into the canvas, no shooting line is rendered until the pen is picked up; at which point the line shoots towards the current pen position.

The program acts as though the stroke is not properly terminated when the stroke ends outside of the canvas. A notification about the pen being "up" is only sent once the canvas starts receiving pen events again (i.e., when the hovering pen re-enters the canvas, or when a dragged pen stops dragging).

Basic system details

MyPaint version: 1.3.0-alpha+git.be1fe883
Operating system: Arch Linux
Desktop environment: GNOME (Wayland session)
Packages: Python 2.7.13, GTK 3.22.15, GdkPixbuf 2.36.6, Cairo 1.14.8, GLib 2.52.1

Steps to reproduce

1. Start MyPaint
2. Begin drawing a stroke towards the edge of the canvas
3. When outside of the canvas, pick up the pen
4. Move the pen outside of the canvas to a new spot
5. Have the pen re-enter the canvas
6. MyPaint draws a line from the end of the rendered towards the pen's new position

MyPaint_Issue_Video.zip

[achadwick]

Confirmed under libgtk-3-0 3.22.11, gnome-core 3.22, and xserver-xorg 7.7+19.

If you inject a 5 second "hands off" delay before step 5, does it happen? For me, it doesn't. If I let it time out (~ a second or two) outside the canvas, the glitch doesn't happen. This is because the brush engine signals that a time-based undo split is due.

Very related: #175.

This leads me to think that we should do a brushwork_commit() on leave-notify and enter-notify events from each known tdw. The interesting part will be queuing such an instruction in gui/freehand.py.

I think proximity in/out events and maybe button1 presses should do the same.

[jigpu]

I can confirm that leaving the pen outside of the canvas for at least 5 seconds (before step 5) does prevent the creation of a shooting line.

[zb13y]

This can be related to problems with windows version. There are problems with mypaint window, sometimes locating under other windows. #586 #677