Path-Union moves the path(s) slightly

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Stefano1337
Posts: 6
Joined: Mon Jun 30, 2008 7:34 am

Path-Union moves the path(s) slightly

Postby Stefano1337 » Fri Feb 27, 2009 6:46 pm

Hi

i noticed a while ago a little annoyance when applying union on one or more paths, the path moves slightly. When trying to replicate the problem, i found that it seldomly doesn't happen.

It bugs me a little bit, because i often do things to be pixel perfect, i.e. very sharp one pixel lines and so on.

Is this behaviour wanted, a bug or could it be my fault?

Slow Dog
Posts: 180
Joined: Wed Sep 24, 2008 7:51 pm

Re: Path-Union moves the path(s) slightly

Postby Slow Dog » Fri Feb 27, 2009 8:07 pm

You say "it seldomly doesn't happen". I'm not clear whether you mean "On rare occasions it moves the path" or "On rare occasions it doesn't move the path".

Do the paths have different stroke widths before the union? The union gives the unionised path the stroke width of one of the initial two, and you could be misinterpreting that as movement.

Stefano1337
Posts: 6
Joined: Mon Jun 30, 2008 7:34 am

Re: Path-Union moves the path(s) slightly

Postby Stefano1337 » Fri Feb 27, 2009 8:32 pm

by "it seldomly doesn't happen" i meant "On rare occasions it doesn't move the path".
This is the reason why i assume that this behaviour is unwanted, allthough the reason why sometimes it doesnt move the path could be something i've missed, not that i touched the settings any time in between.
i also don't have a stroke on the path in question.

here's how to replicate the problem:

open inkscape
draw a rectangle
remove stroke
make sure the rectangle has size in full pixels (e.g. 32x32)
make sure the rectangle's position is on full pixels (e.g. 0, 0)
hit Ctrl+plus
check the Y position (was -0,000 is -0,013)

the same thing happens when subtracting two paths, but not when converting an object to path.

Slow Dog
Posts: 180
Joined: Wed Sep 24, 2008 7:51 pm

Re: Path-Union moves the path(s) slightly

Postby Slow Dog » Fri Feb 27, 2009 9:17 pm

I got the same when I performed a subtraction, for an object bottom-left. Following a hunch, based on a dim recollection that in the internal representation top-left is the real coordinate base, trying the same thing top-left was fine. I suspect that the bug is thus a result of a rounding error.

Stefano1337
Posts: 6
Joined: Mon Jun 30, 2008 7:34 am

Re: Path-Union moves the path(s) slightly

Postby Stefano1337 » Fri Feb 27, 2009 9:38 pm

Slow Dog wrote:I got the same when I performed a subtraction, for an object bottom-left. Following a hunch, based on a dim recollection that in the internal representation top-left is the real coordinate base, trying the same thing top-left was fine. I suspect that the bug is thus a result of a rounding error.


yes, same here.

additionally, if i have an object with uneven proportions on the top right and perform addition or subtraction, the position remains but the size changes

i've made a little illustration which is attached to this post.
the image has to be opened with inkscape, since all the action happens outside the page

edit, the illustration features a bug of it's own. it should say y-position where it says x-position...
Attachments
bug.svg
Inkscape Union&Subtraction Bug Illustration
(89.77 KiB) Downloaded 204 times

User avatar
loonquawl
Posts: 135
Joined: Thu May 15, 2008 7:57 pm

Re: Path-Union moves the path(s) slightly

Postby loonquawl » Fri Feb 27, 2009 9:53 pm

Could not replicate the problem, both with your measurements(32x32 on 0,0), and with own (32x64 on 0,1000), on .46 and .46dev(13.feb) on XP


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