bugMyPaint - Bugs: bug #20405, Under rare circumstances first...

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bug #20405: Under rare circumstances first stroke drawn incorrectly

Submitted by:  Libra Rian <zrzz>
Submitted on:  Fri Jan 4 10:37:34 2013  
Severity: 2 - MinorPriority: 5 - Normal
Status: ConfirmedPrivacy: Public
Assigned to: NoneOpen/Closed: Closed
Release: 1.1.0@git 1635035Planned Release: None
Operating System: Lubuntu 12.10/Compiz

Mon Jun 23 22:23:02 2014, comment #4:

We're migrating bugs to Github, and this one is suitably confirmed and reproducible to be migrated straight across. Thanks for the original report.

You can watch this bug evolve at https://github.com/mypaint/mypaint/issues/11 from now on.

Andrew Chadwick <achadwick>
Project Administrator
Mon Jun 23 15:07:51 2014, comment #3:

Confirmed in git master as of fc4fafa (Sun Jun 22 17:25:57 2014 +0100)

Andrew Chadwick <achadwick>
Project Administrator
Fri Jan 4 17:48:06 2013, comment #2:

This longstanding bug is part of our secret plan to discourage people from trying to do drawing/painting with the mouse ;-)

It's got to do with initialization of low-pass filters - they initialize themselves whenever there is motion (and with a tablet, there is always motion).

Martin Renold <martinxyz>
Project Administrator
Fri Jan 4 13:18:21 2013, comment #1:

Confirmed here, Xubuntu 12.04 and d11113c. A good way to reproduce it is to start mypaint using the keyboard only and start the 1st stroke by pressing the mouse button in a way which simultaneously propels the mouse downwards.

Andrew Chadwick <achadwick>
Project Administrator
Fri Jan 4 10:37:34 2013, original submission:

1) start mypaint
2) Do NOT move mouse.
3) From current position very quickly draw line with mouse
4) Mypaint might add unexpected hook to the beginning of the line. (see screenshot: I've drawn vertical line, diagonal line was added by mypaint)

AFAICT this happens due mypaint-brush.c\ mypaint_brush_stroke_to due its usage of states at line 790:

fac is calculated from dtime and slow position tracking setting of brush(In my case it is 1.03 of deevad/pen).

Upon initialization states are zeroed, so calculated value is lower than it's supposed to be.

If mouse is moved before drawing, then motion_notify_cb at canvasevent.py:519 will call stroke_to with zero pressure, so coordinate states will be updated. However if stroke_to with pressure is called immediately without moving mouse, then weird thing might happen

Libra Rian <zrzz>


Attached Files
file #16895:  screenshot.jpg added by zrzz (50kB - image/jpeg)


Depends on the following items: None found

Items that depend on this one: None found


Carbon-Copy List
  • -unavailable- added by martinxyz (Posted a comment)
  • -unavailable- added by achadwick (Posted a comment)
  • -unavailable- added by zrzz (Submitted the item)

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    Follow 3 latest changes.

    Date Changed By Updated Field Previous Value => Replaced By
    Mon Jun 23 22:23:02 2014achadwickOpen/ClosedOpen=>Closed
    Fri Jan 4 13:18:21 2013achadwickStatusNone=>Confirmed
    Fri Jan 4 10:37:34 2013zrzzAttached File-=>Added screenshot.jpg, #16895
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