[cairo] Paths as paths

[mental at rydia.net]

Quoting Carl Worth <cworth at redhat.com>:

> It *might* make sense to create a separate, high-level, output
> backend for cairo, that would be suitable for creating
> resolution-independent PDF, or editable SVG. But then again, it
> might not. Cairo wouldn't be providing much in this case, as it
> would just be passing data directly from the user to the various
> backends. And there would be a ton of things that PDF/SVG file
> creators would like to do that would be unavailable. So, we'd
> end up with a very limited PDF/SVG abstraction layer, that
> happens to have the same API as the display/print drawing
> layer. Would that be useful?

Based on my thinking about these issues for Inkscape, I think
"structure-preserving" PDF/SVG output is best left as the province
of a retained-mode API with different backends (one for rendering
with Cairo, one for SVG export, etc...), where the requisite
structural information would be readily available.

-mental