[cairo] Creating paths "off-line"

[Fontana Nicola]

I'm starting to develop a canvas for technical drawings based on Cairo and, 
for performance and other reasons, I've separated the geometric construction 
and the render process. This means that, when I'm building the drawing, I 
don't have any Cairo context.

I don't like to provide solutions as creating paths on a dummy surface, so my 
canvas has some functions in the Cairo API style that dinamically add path 
portions to a cairo_path_t struct.

Well, as you can imagine, all is easy if you don't have cairo_arc[_negative] 
to wrap. 

I'm going to include in my project a modified copy of cairo-arc.c.

A better solution? Any suggestion will be appreciated.

-- 
Nicola