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I'm using a set of svg icons in my applications, and I'm painting them using librsvg. These icons are all single-colour black drawings, and I can only draw them black because that is the colour written in the svg file.

There is a way I can to choose, at runtime, the colour (and possibily the alpha channel) of the icon just before painting them, without making a dedicated svg file for any colour I need? Can I make librsvg to ignore the colours written in the svg file and use only the one of my choice? Or any other workaround to have the same effect?

I'm thinking about loading the svg file content and modify in-memory the colour declarations, it should work, but I'm looking for a cleaner way.

Thanks.

user6369958
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    Do I understand correctly that the icons are either "there is nothing here" (aka: transparent) or "this is black" (so no transparency at all here)? If so, you can use the icons as a mask in cairo via `cairo_mask_surface` (after having painted them to some temporary cairo surface via librsvg). – Uli Schlachter Feb 03 '19 at 09:25

1 Answers1

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You may want to monitor https://gitlab.gnome.org/GNOME/librsvg/issues/379 for a clean way to do this. In summary, librsvg needs an API to let you pass in an extra CSS stylesheet; this way your shapes can obtain their colors from that CSS.

https://gitlab.gnome.org/GNOME/gtk/issues/1471 mentions the way in which GTK hacks around this, and you may be able to use something similar. In short, it creates a wrapper SVG like this:

<svg ...>
  <style type="text/css">
    ... extra styling here ...
  </style>
  <xi:include href="... original SVG encoded as a data:URL ..."/>
</svg>

(but check the actual source code in the comments there for the correct syntax!)

Federico Mena-Quintero
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