[cairo] set_source_rgb vs set_source_rgba [Performance]

Peter Clifton pcjc2 at cam.ac.uk
Sat Aug 23 04:14:11 PDT 2008

On Fri, 2008-08-15 at 09:13 -0700, Charles Doutriaux wrote:
> One thing I noticed with postscript output,
> Say you're using a ppattern of stripes to fill a region
> Once converted to postscript if you used rgb, you'll have black stripes 
> where there's "no" data (i.e the empty stripe part)
> whereas if you really use rgba you do obtain the transparency effect. 
> And it DOES also affect the size of the postscript of course.
> By the way I always wondered why the black stripes? I can understand 
> that it's not transparent, but i would have guess for white stripes 
> instead of black.

This behaviour (or one similar to it) has been observed printing in
Windows in the "gerbv" program. (A Circuit board design CAD/CAM file

I've attached the .png which was sent with that bug report.

Does look like the same problem you were seeing?


Are we just doing something wrong assuming the background will be
white / transparent when drawing on this surface?

Peter Clifton

Electrical Engineering Division,
Engineering Department,
University of Cambridge,
9, JJ Thomson Avenue,

Tel: +44 (0)7729 980173 - (No signal in the lab!)
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