[cairo] set_source_rgb vs set_source_rgba [Performance]

[Peter Clifton]

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
viewer)

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

Does look like the same problem you were seeing?

Cario-gurus:

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,
Cambridge
CB3 0FA

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