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issues with facealpha and different image formats

From: Francesco De Vita
Subject: issues with facealpha and different image formats
Date: Sun, 16 Mar 2014 09:34:44 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Icedove/24.2.0

I'm using Octave 3.8.1 on Debian Testing/Sid.
I'm writing here mainly because of an issue I have with the property
"facealpha". Let's get to an example code:

> graphics_toolkit ("gnuplot")
> # because with fltk octave segfaults
> f1=figure(1);
> hold on;
> grid on;
> axis([0 3 0 3]);
> h=fill([1,2,2,1],[1,1,2,2],'b');
> set(h,'facealpha',0.4);

I'm expeting to see in the plot window a blue transparent square with a
visible grid beneath it, but I only see an opaque pale blue square. This
is not expected.

Now, a side issue is with the print command:

> print('test.eps','-deps','-color','-S640,480');
> print('test.svg','-dsvg','-S640,480');
> print('test.png','-dpng','-S640,480');
> print('test.pdf','-dpdf','-S640,480');

Only the svg file shows the transparent square I wanted, the other
formats show only the aforementioned opaque pale blue square. Also, I'm
expecting to have the exactly same image in different formats but
instead I obtain different images, because different are the line
widths, the grid widths, the font dimension and so on.
In this way I should set every time different options as I print in
different formats. From the user viewpoint this is uncomfortable and a
not expected behaviour.

Am I doing wrong something or is it correct what I reported? Are there
some workarounds? Thank you in advance.

Francesco De Vita

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