trunk: unit selector in tool contexts triggers crash on undo of default units change

[su_v]

With current trunk, a rectangle which has a custom position of the rotation center resizes unexpectedly if this object is selected while the document default units are changed in the 'Document Properties' dialog.

Steps to reproduce:
1) launch current trunk (default prefs, default new doc, locale: en_US)
2) draw a rect
3) move the rotation center away from default position
4) keep rect selected
5) open 'Document Properties' and change default units (e.g. to 'mm')

Expected result:
The rulers reflect the change of the default units, the object(s) on-canvas stay unchanged (same size & position relative to page area)

Actual result:
The selected object changes in scale when default units are changed.

Inkscape crashes when attempting to undo the latest changes:
6) close 'Document Properties'
7) apply 'Edit > Undo' (or 'Ctrl+Z') twice

--> crash:
**
ERROR:../../src/document-undo.cpp:158:static void Inkscape::DocumentUndo::maybeDone(SPDocument *, const gchar *, const unsigned int, const Glib::ustring &): assertion failed: (doc->priv->sensitive)

Based on tests with archived builds on OS X 10.7.5:
- not reproduced with stable 0.48.4, 0.48.5
- not reproduced with 0.48+devel rev <= 12552
- reproduced with 0.48+devel rev >= 12555;
this regression appears to be related to the merge of the GSoC unit-improvements branch in r12554:
<http://bazaar.launchpad.net/~inkscape.dev/inkscape/trunk/changes/12555>

Reproduced with Inkscape 0.48+devel r13466 on OS X 10.7.5.

[su_v (suv-lp)]

The regression appears to be triggered as soon as a rectangle earlier in the stack has a transformed rotation center - any rectangle stacked above and selected while default units are changed will get rescaled.

[su_v (suv-lp)]

Backtrace (crash on undo) attached (Inkscape 0.48+devel r13504, OS X 10.7.5, debug build).

(thx to LiamW for notifying me about the crash on undo)

[su_v (suv-lp)]

Raising importance (crash when attempting to undo the unexpected changes)

[Alvin Penner (apenner)]

attached is a proposed patch for this bug.
This effectively disables all of the center-specific code in the routine SPGroup::scaleChildItemsRec().
I believe it fixes the original bug report.
I cannot tell if it fixes the crash or not, because I have not been able to reproduce the crash.

It does not fix Bug 1247799.
There is still a need for further work to be done in this area because the underlying problem is that the scaling rules for 'inkscape:transform-center-x' are not the same as for 'width', when they should be the same:
- if you scale a rectangle using the mouse then both the 'inkscape:transform-center-x' and 'width' will scale by the same factor, as expected.
- if you scale a rectangle by changing document units, then the numerical value of 'width' will change to the new units, but 'inkscape:transform-center-x' will remain unchanged in numerical value, which is inconsistent. See also https://bugs.launchpad.net/inkscape/+bug/1247799/comments/7

[su_v (suv-lp)]

Sorry for the delay in testing with recent commits:
Based on tests with recent archived builds (on OS X 10.7.5):
- reproduced with r13511
- not reproduced with r13512
this seems to have been fixed too by Diederik's recent commit in revision 13512.
<http://bazaar.launchpad.net/~inkscape.dev/inkscape/trunk/revision/13512>

Please reopen if this report was closed in error and can still be reproduced in current trunk >= 13512.

[su_v (suv-lp)]

Not fully fixed: still crashes on undo.

[Alvin Penner (apenner)]

Windows XP, running rev 13520, with a little messy patch to allow it to link, crash reproduced

ERROR:src/document-undo.cpp:158:static void Inkscape::DocumentUndo::maybeDone(SPDocument*, const gchar*, unsigned int, const Glib::ustring&): assertion failed:
(doc->priv->sensitive)

[Alvin Penner (apenner)]

I should explain the "patch" comment, there is a temporary link error, see

http://inkscape.13.x6.nabble.com/Windows-XP-cannot-compile-rev-13520-td4971192.html

[Alvin Penner (apenner)]

the crash can be reproduced even if the center of rotation is kept at its' default value.

- draw rectangle
- change units from px to mm
- select rectangle
- ctrl-Z to undo, get crash

it is not necessary for the rectangle to be selected when changing units, but it is necessary for it to be selected when performing ctrl-Z

[Alvin Penner (apenner)]

as far as I can tell, the crash occurs only with rectangles, not with any other shapes

[Alvin Penner (apenner)]

what makes the rectangle unique is that the rectangle toolbar has a units selector in it. This units selector is linked to the default document units in the document properties dialog. The linkage is one-way, meaning that a change in rectangle units will not affect the document units, but any change in document units will affect the rectangle units. This linkage is apparently triggering the crash.

[Alvin Penner (apenner)]

crash can also be reproduced as follows:

- draw Bezier curve or line
- change default document units
- select node tool F2
- click on a node
- hit ctrl-Z to undo
- get crash message:

ERROR:src/document-undo.cpp:162:static void Inkscape::DocumentUndo::maybeDone(SPDocument*, const gchar*, unsigned int, const Glib::ustring&): assertion failed:
(doc->priv->sensitive)

- also reproduced by using the freehand line (F6) in the first step above
- also reproduced with calligraphy tool (ctrl F6) in first step

[Alvin Penner (apenner)]

crash avoided by adding new restriction on when updates can occur
committed to rev 13547