Bug#502502: librsvg2-bin: does not position text correctly for rsvg-view

[Alan W. Irwin]

Package: librsvg2-bin
Version: 2.22.2-2
Severity: important


I have just finished debugging the SVG device for PLplot, and it produces
SVG-1.1 results that validate at http://validator.w3.org/check and which
view fine (i.e. have perfect text positioning and good graphics) on firefox
and konqueror.  I also have reports that inkscape and karbon14 imports these
files with no problems.  The same reporter says the latest stable release of
scribus imports them fine but with text that is misplaced by various small
amounts. However, along with that second-hand report came the information
that scribus has a much improved svg import facility in their svn version.
Therefore, I built the most recent svn snapshot of scribus-ng, and that
imports PLplot SVG results with exact text positioning and good graphics
just like viewed by firefox and konqueror.  So the conclusion is that the
PLplot SVG results are a high-quality set of validated SVG files that are
rendered correctly by most viewers and SVG editors.

The librsvg-based ImageMagick "display" application and also rsvg-viewer are
an exception to this pleasant result.  The PLplot SVG results are displayed
with a variety of small but annoying shifts to the text positions. Since
rsvg-viewer clearly shows the problem I am reporting it for librsvg2-bin,
but it is likely a problem in librsvg2-2 itself since the ImageMagick
"display" application also shows the identical text positioning problems.

I will follow up this bug report with a simple svg file example consisting
of a long vertical line, a horizontal line marking the exact midpoint of
that line, and the text string "HHHHHHH" written parallel to the long
vertical line and centred on its midpoint using the text-anchor="middle"
attribute for the text tag.  If you view that SVG file with iceweasel
(firefox) or konqueror or the equivalent of konqueror called svgdisplay, the
"HHHHHHH" string is centred perfectly.  But not so for rsvg-view (or
display) which show a text shift of about a third of a character. If you
hand-edit the file to change "HHHHHHH" to "H" the result is centred
perfectly for all viewers (including rsvg-view and display). A change from 7
identical characters to 1 should not change the position of the middle of
the string so this is clear independent evidence that the problem is in
librsvg2-bin or its librsvg2-2 dependency.

I emphasize the file I will attach later is just one simple example to make
a clear point, but the problem does not occur for just text-anchor="middle"
alone for our 30 complex standard plotting examples.  All those examples
show text shifts from what firefox displays which are typically half a
character or less (like the present example). If you feel you have a fix for
this simple example, I would be glad to check how well the fix works for all
30 of the standard PLplot examples.

If you do decide to boot this upstream rather than attempt to fix the
problem yourself, please tell me where you do so since I would like to
follow the response there and also perhaps participate in the discussion/
help with testing fixes.

-- System Information:
Debian Release: lenny/sid
  APT prefers testing
  APT policy: (990, 'testing'), (500, 'unstable')
Architecture: amd64 (x86_64)

Kernel: Linux 2.6.26-1-amd64 (SMP w/2 CPU cores)
Locale: LANG=en_CA.UTF-8, LC_CTYPE=en_CA.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash

Versions of packages librsvg2-bin depends on:
ii  libc6                         2.7-14     GNU C Library: Shared libraries
ii  libcairo2                     1.6.4-6    The Cairo 2D vector graphics libra
ii  libglib2.0-0                  2.16.6-1   The GLib library of C routines
ii  libgtk2.0-0                   2.12.11-3  The GTK+ graphical user interface 
ii  librsvg2-2                    2.22.2-2   SAX-based renderer library for SVG
ii  libx11-6                      2:1.1.5-2  X11 client-side library
ii  python                        2.5.2-2    An interactive high-level object-o

librsvg2-bin recommends no packages.

librsvg2-bin suggests no packages.

-- no debconf information