[gl2ps] Blending/transparency support

[Christophe Geuzaine]

> On 11 Sep 2016, at 19:56, Pantxo Diribarne <pantxo.diribarne at gmail.com> wrote:
> 
> Hi,
> 
> I see there are a few words of caution in the documentation about blending and transparency. As we want to enable blending in Octave, I'd like to know what is the status of blending in gl2ps. In particular those two
> 
> >>" Transparency is only supported for PDF and SVG output. " 
> 
> AFAICS from the output of gl2psTest, transparency doesn't work for PDF output.

Support is partial, but it should work: at least on my machine, running gl2psTest with blending enabled ("b") and PDF format, the "simple sort" result looks ok.

> As for svg, transparency seams to be enabled whatever the state of GL_BLEND. Are those known issues?
> 

Yes, indeed: for SVG we bypass the glIsEnabled(GL_BLEND) test. I don't remember what the rationale was for this...

> >> "GL2PS_BLEND:Emulates the GL_BLEND functionality. (Warning: this might change in future releases.)"
> 
> What might change? 
> 

It was not clear at the time we coded this if our implementation was the right way to go. I'm not sure how many people use GL2PS with blending (I don't...) - but we should probably remove the warning.

Christophe

> Pantxo
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-- 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science 
http://www.montefiore.ulg.ac.be/~geuzaine

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