Union adds bogus node

[aditsu]

Inkscape 0.48 as well as trunk (r10068) on Gentoo Linux.
See the attached file, test.svg - there are 8 paths, each one with 4 nodes, and each node matches a node from another path. If I select all the paths and do union, a new node gets added in the inner top left area. The new node is not only unnecessary, but it actually makes the arc go a little bit above the top line, thus making the inner shape concave.

[aditsu (aditsu)]

Same problem happens when the paths are already joined (so there's only one path on which I do union). I've actually broken apart the inner and outer paths and kept only the inner one, see the attached file.

[su_v (suv-lp)]

Possibly related to bug #168158 “Path Boolean operations are imprecise”
<https://bugs.launchpad.net/inkscape/+bug/168158>

[su_v (suv-lp)]

Reproduced with the attached sample drawing 'test.svg' in Inkscape 0.48+devel r10067 on OS X 10.5.8 (i386).

However, not reproduced with attached sample '723559-test-3.svg', using the same paths, but with drawn with more precision:
- all coinciding nodes really coincide
- all nodes are snapped to full pixel values (as seen in the XML Editor, related to the SVG coordinate system in the upper left corner, and a page height with full pixel value - no decimal places like with default A4).
- 2 redundant nodes of each corner piece removed

In '723559-test-3.svg', no additional node is inserted into the result after unioning the 8 paths.

[su_v (suv-lp)]

Same for 'test2.svg':

Reproduced as is with current trunk (r10067).

Not reproduced when
- nodes snapped to full pixel positions (relative to SVG coordinate system origin)
- handles of all straight line segments retracted

In '723559-test2-2.svg' (attached) no additional node is inserted after unioning the path with itself.

IMHO this is a duplicate of or at least closely related to bug #168158 (see comment #6 there).

[aditsu (aditsu)]

I hadn't noticed the imprecise positions before reporting the bug.
Indeed, the problem seems related to the other bug.
Let me know if I can help fix it. I'm fairly good at algorithms but my C/C++ is a bit rusty and also I don't have plenty of spare time.

[Beluga (buovjaga)]

No repro with test.svg. Please re-test.

Arch Linux 64-bit, KDE Plasma 5
Inkscape 0.92pre1 15054 (GTK3)

[jazzynico (jazzynico)]

Bug reproduced on Windows XP (32-bit), Inkscape 0.48.5.
Not reproduced with 0.91 and lp:inkscape/0.92.x rev. 15214.