Interpolate extension creates wrong stroke width

[Hachmann]

Using the interpolate extension in Inkscape 0.92pre1 from May 27th 2016, I get unexpected path widths when I interpolate two objects (with the same path width or not, no matter if the interpolate style option is selected). The width is roughly 26% of the initial width.
Using mm as document unit.

(Edit: Unrelated and covered by another report already: The extension also seems to create open paths out of my closed paths. This happens in 0.91, too, if I'm using the same path (copy-pasted from 0.92pre1 to 0.91).)

[su_v (suv-lp)]

The 'closed paths are opened' issue is unrelated to the units issue and likely already covered by:
* Bug #202540 “Modify path effects open closed paths”
  https://bugs.launchpad.net/inkscape/+bug/202540
(a limitation of the cubicsuperpath module which currently does not preserve 'Z' path commands)

If not covered by bug #202540, or if it can be fixed without refactoring csp, this aspect needs to be filed and tracked separately.

[Hachmann (marenhachmann)]

Thanks, V, I'll update the description.

[su_v (suv-lp)]

Patch to fix interpolating stroke widths - please test.

[Hachmann (marenhachmann)]

That works very well for me, thank you, V!

[su_v (suv-lp)]

@JazzyNico - please milestone to 0.92 (it's not strictly a regression: while already present in 0.91, the incorrect stroke width interpolation is not exposed with default new documents there).

[jazzynico (jazzynico)]

Milestoned to 0.92.
And more patch to test and commit in my long todo list.

[Jabiertxof (jabiertxof)]

@jazzynico ping me if you want help, when you want.

[jazzynico (jazzynico)]

@Jabier - Thanks! Most of my tasks are related to documentation, translation and extensions, plus some patch that need to be tested. Don't hesitate to try this one or others attached to other reports linked to 0.92. The more we test, the better it is!

Apart from it, it would be really great if every developer could review the reports related to their favorite part of the Inkscape code and try to fix some of them (preferably crashes and regressions). Inkscape already has lots of features, but needs some polish now. I'm pretty sure there are some LPE bugs you could fix (there are currently 54 open bug tagged LPE, 11 are high importance and 5 are regressions -not all recent). Would you be willing to take a look?

[Jabiertxof (jabiertxof)]

Yes this weekend go into!

[jazzynico (jazzynico)]

Patch successfully tested on Xubuntu 16.04, Inkscape 0.92.x rev. 15048 and trunk rev. 15080.

[jazzynico (jazzynico)]

and committed in the 0.92.x branch (rev. 15049) and trunk (rev. 15081).

Thanks for the patch, su_v!