Linked offsets regression

Attached is a simplified version of the shapes-f17 image (Shapes tutorial) that shows the error messages and produces invalid tutorial files.

Also note that the offsets are shifted when opened with Inkscape trunk (ok with 0.48), but I'm not sure it's directly related to the same bug (not reproduced with new offsets in a blank document).

Console warnings on load not reproduced with Inkscape 0.48+devel r10516 on Mac OS X 10.5.8 (i386), compiled with '-g -O0', default new preferences - tested with attached sample file, 'Advanced' tutorial from the help menu as well as a newly created file with linked offsets of a star, a simple bézier path and a text object.

(Displaced - shifted - linked offsets of the attached sample file confirmed with default new preferences file, seems unrelated to the console warnings seen on Ubuntu 10.10)

> CRITICAL **: Geom::Affine SPItem::i2dt_affine() const: assertion `desktop != NULL' failed

Reproduced when opening the attached SVG file as command line argument instead of using the GUI (File > Open…).

Likely related to the fix for bug #815926 - inkscape no longer crashes with the fix in r10505, but produces above message(s) when opening a file as command line argument.

No big worries about the warnings necessary.
The warnings are there to remind us that there is some refactoring left to do. It should in no way alter behavior from released versions. (in fact, when you see this warning, inkscape defaults to behavior from the past.)

Unfortunately the displacement problems was introduced by my patch for making the behavior of linked offsets match the behavior of clones (It was a prerequisite for me in order to fix some bugs with linked offsets). By changing this, linked offsets started taking into account the transform of the original object into their rendering process. This means that objects that have a transformation matrix attached to them will have their linked offsets transformed by that matrix as well as their own matrix.

I think that the original intention was to make linked offsets behave like clones, but on the other hand people have started depending on the old behavior.

I have already contacted the developer mailing list to see what their opinion is on this.

Raising importance based on new duplicate report for Inkscape 0.48.3.1: AFAICT there is no workaround to render transformed linked offsets of transformed originals in old documents correctly.

The console warnings are no longer present when opening affected files from the command line.

Related discussion on the mailing list:
 <http://thread.gmane.org/gmane.comp.graphics.inkscape.devel/37132>

~Adonis - Since the new behavior seems to be widely accepted, there's no reason to annoy you with that bug, and I'll try to modify the SVG file so that it works with the new Inkscape versions.

Fixed in the doc trunk, revision 470.
Shape tutorials update in progress.

Tutorial update committed revision 11704.