Filter effects and blur quality options broken

[jazzynico]

Reproduced on Windows XP with Inkcape 0.91 and trunk rev. 14440.
Not reproduced with 0.48.5.

Steps:
1. Open the attached file (a simple ellipse with marble effect).
2. Open the Inkscape preferences > Rendering tab.
3. Set the Filter effect quality options to Lowest quality.
4. Refresh the canvas (move the object of zoom-in, zoom-out) -> no change.
5. Set the Filter effect quality options to Highest quality.
6. Refresh the canvas -> again, no change.

Can also be reproduced with a blurred object.

[su_v (suv-lp)]

Reproduced with Inkscape 0.91 and 0.91+devel r14441 on OS X 10.7.5.

Based on tests with archived builds:
- not reproduced with r10326 (just after the merge of the cairo rendering branch)
- reproduced with r10588 (just before the removal of libnr)
the regression seems to have been introduced between r10326 and r10588.

Possibly related major commits (speculative for now):
* Merge SPCanvasArena caching layer work in r10451:
https://bazaar.launchpad.net/~inkscape.dev/inkscape/trunk/revision/10451
* Merge rendering cache branch (GSoC 2011) in r10579:
https://bazaar.launchpad.net/~inkscape.dev/inkscape/trunk/revision/10579

[su_v (suv-lp)]

On 2015-11-03 16:35 (+0100), ~suv wrote:
> Possibly related major commits (speculative for now):
<...>
> * Merge rendering cache branch (GSoC 2011) in r10579:
> https://bazaar.launchpad.net/~inkscape.dev/inkscape/trunk/revision/10579

Further tests with (new) builds of related revisions:
- not reproduced with rev 10578,
- reproduced with rev 10579;
it seems likely that the regression is related to the changes in r10579.

[jazzynico (jazzynico)]

The attached patch is just a quick and dirty fix.

@Tweenk - Could you please take a look and see if an elegant fix can be applied before we release 0.91.1? Thanks!

[jazzynico (jazzynico)]

Fixed in the trunk rev. 14913.

[su_v (suv-lp)]

Related follow-up report:
* Bug #1656383 “Artifacts in rendering of Gaussian blur filter
                (horizontal stripes)”
  https://bugs.launchpad.net/inkscape/+bug/1656383

The artifacts reported in bug #1656383 might have been exposed with the changes in r14913 to re-activate the quality settings, and possibly are related to changes already in the initial implementation of the new cairo-based renderer.