ungrouping didn't preserve appearance

[James]

Ungrouping a plot from gnuplot led to a black box covering the entire frame. attached the test case.

the origin of this bug has been pinpointed here:
https://bugs.launchpad.net/inkscape/+bug/174720/comments/13

[Martin von Gagern (gagern)]

Thanks bbyak for pointing me at sp_style_merge_from_dying_parent in bug #174720 comment #18.
With this information I was able to track this down fairly quickly. The "none" setting wasn't merged down, as it wasn't handled at all in sp_style_merge_ipaint. The attached patch fixes that.
This should be tested thoroughly, though, as I could imagine some other parts of the code could assume that noneSet implies set, which is no longer true.

The attached patch also modifies the behaviour of ungrouping in the light of currentColor. When the child of a dying parent has some property explicitely set to currentColor, then it should be kept that way, not set to the value from the parent. The color property itself gets merged like any other normal color specification.

[James (lf010)]

I can confirm that Martin's patch fixed the bug for the test case and other plots in which I previously observed this bug. thanks!

[bbyak (buliabyak)]

thanks for the fix, committed

noneSet was actually not used anywhere yet except in not writing stroke props if stroke is none, so this should not have any side effects