Filter applied on group does not auto redraw when edited

[Alvin Wong]

If a filter is applied on a group (including Inkscape Layers, which can be done by manually adding the style with XML Editor), editing the filter does not update the rendering of the group unless the filter is reapplied manually, or toggling the visibility of the layer (can be the layer itself which the filter is applied on).

Example steps to reproduce:

1. Draw two shapes.
2. Group the two shapes.
3. Create a filter in the "Filter Editor" and add a "Flood" effect. (The group should be filled with the flood colour but this doesn't happen immediately.)
4. Hide and unhide the current layer to see the filter effect applied.
5. Change the "Flood Color". (The rendered colour should change but doesn't.)

Also affects objects like 3dboxes (internally stored as group containing 6 paths) when merging multiple preset filter effects (see duplicate bug #1435078).

Affects versions: rev >= 12648 (inc. 0.91)
Regression introduced on: rev 12648 http://bazaar.launchpad.net/~inkscape.dev/inkscape/trunk/revision/12648

[su_v (suv-lp)]

Reproduced on OS X 10.7.5 with 0.91 r13725 and 0.91+devel r13941;
tests with archived builds confirm that the regression seems to be a side-effect of r12648 (fix for bug #304407).

[Alvin Wong (alvinhochun)]

Apparently, reverting the changes to `sp-item-group.cpp` (https://bazaar.launchpad.net/~inkscape.dev/inkscape/trunk/revision/12648/src/sp-item-group.cpp) is enough to fix this bug. Tested on 0.91 Windows 64-bit.

[su_v (suv-lp)]

Attaching the proposed change as diff against trunk r13950 to ease further testing.

[su_v (suv-lp)]

Patch tested successfully with 0.91+devel r13950 on OS X 10.7.5; so far, no regressions noticed when testing against the 'steps to reproduce' provided in bug reports known to have been fixed by r12648:
Bug #243729 “Grouping filtered text objects looses rendering of filter effects”
Bug #304407 “After ungrouping or decoupling a clone blur is no longer shown but style attribute still present.”
Bug #930593 “Grouping/ungrouping of filtered objects (groups|texts|clones) makes them disappear temporarily”

[su_v (suv-lp)]

<off-topic>
Detail likely not really relevant to this report (bug #1425542): when repeating the steps to reproduce mentioned in comment 4 (e.g. group an object (a clone, or a text) and its blurred clone), Inkscape 0.91+devel r13950 (with or without patch) produces this console message:

** (inkscape:62042): CRITICAL **: void SPObject::requestModified(unsigned int): assertion 'this->document != NULL' failed
</off-topic>

[jazzynico (jazzynico)]

Fixed in the 0.92.x branch (rev. 15051) and trunk (rev. 15083).
Credit to Alvin (fixed thanks to his comment #2).
Thanks:!