[cairo] Implementing PCL's display model using cairo.

Wolfgang Glas wolfgang.glas at ev-i.at
Tue May 10 00:56:58 PDT 2005

Am Montag 09 Mai 2005 20:10 schrieb Carl Worth:
> On Mon, 9 May 2005 09:45:01 +0200, Wolfgang Glas wrote:
> > > >   Moreover, I played a bit with the PDF display model, which is
> > > > claimed to be represented by cairo's display model. In PDF, I could
> > > > map my 4 operations in a suitable way by choosing the following
> > > > mapping:
> > > >
> > > > 1) Lighten
> > > > 2) Darken
> > > > 3) Exclusion
> > > > 4) Normal
> Operators like these are fundamentally different from bitwise
> operators such as AND, OR, and XOR. It's quite feasible that the PDF
> operators could be added, (it just requires someone doing the
> work). But I am quite certain that bitwise operators will never appear
> in cairo[*].

Yes, I know this. Since I already dived into the PDF specification, I can try 
to add some of the PDF operators to cairo, but it may take some time, because 
I'm quite busy these days...

Coming back to my HPGL/PCL renderer, I could produce good results with 
PDF-like arithmetic operators, which gave pretty much the same results as 
PCL's ROP operations. This is mostly due to the fact, that almost any 
technical plot uses fully saturated colors. 

> > IMHO completing the set of perators should be an integral part of the API
> > shakeup process, which is currently in progress.
> API-wise, new operators are very easy to add at any time. It's simply
> a matter of extending an existing enum, so there's nothing
> backwards-incompatible here.

OK, I'll have a look at the code any try to add at least the PDF-style 
'Darken' and 'Lighten' operations.

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