trunk: scaling of stroked clipped objects broken (rev >= 12863)

[su_v]

Steps to reproduce:

1) launch trunk with default (new) prefs
2) open attached document
3) select both rectangles
4) apply menu 'Object > Clip > Set'
5) grab the lower right transformation handle and start dragging

Expected result:
The clipped object transforms accordingly.

Actual result:
The clipped object disappears (selection appears to be dimensionless, at SVG origin).

Based on tests with archived builds on OS X 10.7.5:
- not reproduced with rev <= 12862,
- reproduced with rev >= 12863;
this regression seems to have been introduced with the initial fix for bug #1262146 in
<http://bazaar.launchpad.net/~inkscape.dev/inkscape/trunk/revision/12863>

[su_v (suv-lp)]

Another example (this time a smaller object clips a larger one):

1) select both ellipses
2) apply clip
3) scale by dragging lower right transformation handle

--> produces odd results, and console messages like these:

** Message: stroke scaling error : 0, 242.647790, 217.642849, 279.999995, 377.642849, 437.142853
** Message: stroke scaling error : 0, 242.647790, 217.642849, 279.999995, 397.642849, 417.142853
** Message: stroke scaling error : 0, 242.647790, 217.642849, 279.999995, 429.071421, 388.571424
** Message: stroke scaling error : 0, 242.647790, 217.642849, 279.999995, 437.642849, 379.999995
** Message: stroke scaling error : 0, 242.647790, 217.642849, 279.999995, 451.928563, 362.857138
** Message: stroke scaling error : 0, 242.647790, 217.642849, 279.999995, 457.642849, 357.142853
** Message: stroke scaling error : 0, 242.647790, 217.642849, 279.999995, 443.357135, 345.714281
** Message: stroke scaling error : 0, 242.647790, 217.642849, 279.999995, 443.357135, 348.571424
** Message: stroke scaling error : 0, 242.647790, 217.642849, 279.999995, 440.499992, 351.428567
** Message: stroke scaling error : 0, 242.647790, 217.642849, 279.999995, 440.499992, 354.285710
** Message: stroke scaling error : 0, 242.647790, 217.642849, 279.999995, 440.499992, 354.285710
** Message: stroke scaling error : 0, 242.647790, 217.642849, 279.999995, 440.499992, 351.428567
** Message: stroke scaling error : 0, 242.647790, 217.642849, 279.999995, 440.499992, 351.428567
** Message: stroke scaling error : 0, 242.647790, 217.642849, 279.999995, 234.785706, 294.285710
** Message: stroke scaling error : 0, 242.647790, 217.642849, 279.999995, 257.642849, 319.999995
** Message: stroke scaling error : 0, 242.647790, 217.642849, 279.999995, 263.357135, 328.571424
** Message: stroke scaling error : 0, 242.647790, 217.642849, 279.999995, 266.214278, 337.142853
** Message: stroke scaling error : 0, 242.647790, 217.642849, 279.999995, 266.214278, 339.999995
** Message: stroke scaling error : 0, 242.647790, 217.642849, 279.999995, 269.071421, 342.857138

[Alvin Penner (apenner)]

thanks, I'll look into it.
It is possible I may be able to borrow code from Bug 811819

[Alvin Penner (apenner)]

implemented Diederik's fix for Bug 811819

committed to rev 13096