Missing handles after reset of rotation center

Based on tests with archived builds (on OS X 10.7.5):
- not reproduced with Inkscape 0.91 r13725,
- not reproduced with lp:inkscape/0.92.x rev <= 15237,
- reproduced with lp:inkscape/0.92.x rev >= 15238,
- reproduced with Inkscape 0.92.0 r15299,
- reproduced with lp:inkscape/0.92.x rev 15322;
it seems that the reported regression was exposed with the changes in r15238:
https://bazaar.launchpad.net/~inkscape.dev/inkscape/0.92.x/changes/15238

Revision 15238: Backport trunk 15293. Add triangle knot.
https://bazaar.launchpad.net/~inkscape.dev/inkscape/0.92.x/revision/15238

Revision 15293: Add triangle knot.
https://bazaar.launchpad.net/~inkscape.dev/inkscape/trunk/revision/15293

Reproduced on Ubuntu 14.04.5 LTS with
- Inkscape 0.92.0 (from stable PPA)
- lp:inkscape r15423 (local trunk build)

@Jabiertxof - any chance you could take a quick whether this could be easily fixed? AFAICT based on my tests, the regression seems related to/exposed with the merge of the triangle knot branch (for mesh gradients).

Actually, the bug is simply triggered by clicking on the rotation center. This happens easily with small objects and requires each time an explicit tool switch to restore the transformation handles (I encountered this many times recently when editing an Inkscape icons file with rather small objects).

Steps to reproduce:
1) launch inkscape (0.92.x)
2) draw a rect
3) click once (LMB) to show the rotation transformation handles
4) click once (LMB) on the rotation center

-> transformation handles are gone, and don't re-appear unless there's a tool switch.

The easiest way to reproduce this thing is to draw a rectangle and just click at any handle without moving mouse around. If you actually try moving object which handles you've just made disappear, you will be moving that object as if you started dragging it by clicking at point nearest to handle.

this patch fixes the bug

Maybe change milestone to 0.92.2?

The patch is for trunk. Apply to 0.92.x with 3 offset hunks

Patch tested successfully with lp:inkscape/0.92.x r15356 on OS X 10.7.5 - thx a lot, Jabiertxof!

So far, no unintended side-effects encountered (select tool, mesh tool) during a few quick sessions - please everyone who can, test this patch as much as possible: IMvHO it would be great to get this fix accepted for the stable release branch as soon as possible.

I've also finally tested :)

I can no longer trigger the persistent missing handles with the patch. Thank you, Jabier :)

I can still trigger the intermittently missing handles, when clicking on different objects quickly. It doesn't take a click on a handle to get this (or rather, lose this). But I've now found that this issue already exists in 0.91 (and its severity is much lower than this one's).

When clicking around a bit, working with different tools, moving and resetting rotation centers, playing with snapping etc. for a couple of minutes, I couldn't find an adverse effect of the change.

I always worry signal changes might have side effects but this patch looks straightforward enough. su_v says the bug is marked Low priority because an easy workaround exists, but that the user impact of this is severe enough to warrant inclusion in the point release. On the basis of the two independent testers' +1s, this is ack'd for landing on 0.92.x for inclusion in 0.92.1. Get it in quickly though.

A tweak of the patch to noyt call two times to the function on gradient drag

Fixed compiling. Thanks su_v

Fix committed to trunk lp:inkscape in rev 15486:
https://bazaar.launchpad.net/~inkscape.dev/inkscape/trunk/revision/15486

Second patch tested successfully with lp:inkscape/0.92.x on Ubuntu 14.04 and OS X 10.7.5 - AFAICT it's as stable as the first version.

Commited in 0.92.x in r.15364.
Thanks su_v for review it!