[cairo] using cairo_stroke_preserve with transparent color

[ds]

Hay,

I am quite new to cairo. I searched the mailing list and found some
hints back in 2007, but nothing worked for me.

I have a quite simple application. I draw a path, and I want to display
it during painting. Therefore I wanted to use cairo_stroke_preserve.
Especially if I have a big line width the result is not what is
expected. The expected result should be independent of calling
cairo_stroke_preserve inbetween the path I think.

At the point of the path, where cairo_stroke_preserve is called, the dot
with diameter of line width is drawn twice, which makes it look
different due to the alpha chanel (transparency)

Is there any standard way to draw a transparent path with a line width
and make inbetween displaying?

Thanks a lot

Detlef