perspective extention gives strange results

[Erik Ruwalder]

tested in Inkscape 0.92pre5 r15287
Extension / modify path / perspective
Tested with some text + a path and the text is not put in the bounding box of the path as it is in 0.91

[Erik Ruwalder (eruwalder)]

I tested this on a Windows 7 machine.

[Alvin Penner (apenner)]

thank you for taking the time to issue a report.

- problem not reproduced on Windows 10, Inkscape 0.92pre5 r15287
- attached is the result I get. I had to first apply the method 'Path->Object to Path' to the text object, and then apply the Perspective method.
- could you attach your svg file that illustrates the problem?

[su_v (suv-lp)]

This is likely the same issue as reported earlier in
* Bug #1508400 “inkex.py: support arbitrary (but uniform) document scale (0.92)”
  https://bugs.launchpad.net/inkscape/+bug/1508400
It is exposed in Inkscape >= 0.92(preX) when applying certain extensions in SVG documents created with viewBox/viewport dimensions based on 90dpi (either with Inkscape 0.91, or e.g. based on custom user templates originating from Inkscape 0.91).

The 90 vs 96dpi scaling issue with python-based script extensions is now tracked in bug #1525418.

[Erik Ruwalder (eruwalder)]

In the document properties of default.svg in the pre5 release the "scale" setting is not set to 1.00
When I change this to 1.00 the strange behavior with perspective disappears.

[Erik Ruwalder (eruwalder)]

I used the 7zip file to test and not the installer.

[su_v (suv-lp)]

Please attach a test case (Inkscape SVG file created with Inkscape 0.92pre5 before and after applying the extension) to allow further investigation of the reported issue.

[Erik Ruwalder (eruwalder)]

In the first file perspective-scale-wrong.svg, the scale is set to the default
in default.svg (90/96 = 0.9375) then the perspective extension gives the
wrong result.

For the 2nd file perspective-scale-ok.svg, I first changed the scale to 1
and then created the paths and used the perspective extension. Then I get
the correct result.

[Hachmann (marenhachmann)]

Still broken in trunk and 0.92.1 (but I cannot reproduce the fix by setting scale to 1.0, neither with px nor with mm).

[Alvin Penner (apenner)]

confirmed on Windows 10, Inkscape 0.92.1 r15371

the problem is not limited to just legacy documents which have been loaded into a newer version of Inkscape. It also occurs if you modify the Scale in the Document Properties dialog. Attached is a new drawing created in 0.92.1 in which the scale was modified to be 1.5, and then the Perspective was tested. The modified perspective drawing is well off the page, one must zoom out to see it.

[Alvin Penner (apenner)]

attached is a proposed fix for this bug. The new code compensates for the viewbox size using essentially the same method as hpgl_encoder.py
   I will leave this code here for a few days for testing purposes before proposing a merge.

[Alvin Penner (apenner)]

attached is a modified version of the file summersnight.py. This will fix the Modify Path->Envelope extension in the same way as the perspective extension.

[Alvin Penner (apenner)]

merged with trunk in gitlab rev:
https://gitlab.com/inkscape/inkscape/merge_requests/39

thanks Martin!