It is well known that Firefox (even the latest 3.x) does not support text-decoration=”underline” on text elements in SVG. However, it bites me hard when I found out imagemagick does not support that either when rastering svg to pixel images.

After digging around, (by looking at the ebuild file) I found out that imagemagick is actually making use of librsvg to do the heavy lifting when dealing with svg files.

librsvg is part of gnome-base packages (as can be seen in gentoo portage). Looking at the source code, I figured that it makes use of pango to render text.

From the days of working on SCIM project, I know for sure that pango is more than capable of rendering text with underlines. So there must be something missing in librsvg to render it. It turns out that, while the svg parser implemented in librsvg does indeed look for text-decoration, and recoganize underline (among strikethrough and overline), it is not actually making use of these parsed info to render the text.

After a bit of tracing the code, I found out how to patch it: the trick is just to add a pango underline attribute to the text layout, and everything else is taken care of by pango.

This bug is reported to upstream, and hopefully it will be merged there soon. The patch is available in that bug report, so you can grab it if you can’t wait. The patch also fixes a bug which is discovered after the underline problem is fixed: when a underlined text has stroke set, the stroke is rendered in wrong position.