[Rd] re: transparency

Peter Dalgaard BSA p.dalgaard@biostat.ku.dk
10 Aug 2001 19:13:17 +0200

Thomas Lumley <tlumley@u.washington.edu> writes:

> On Thu, 9 Aug 2001, Prof Brian Ripley wrote:
> > However, for the future (1.4.x), I think we should handle "white" and
> > "transparent" differently, and have bg default to "transparent" for
> > all devices.  A quick look shows that this is would be easy, as only
> > 24 bits of the rcolor type are used.  So would there be an objections
> > to using a bit (or a single value) of the upper byte to denote
> > "transparent"?  (Actually, Peter D has 0xffffffff in use as invalid,
> > but that's more bits than are needed.)  For consistency "transparent"
> > should be an alternative to NA in the fill routines, which means that
> > the obvious rcolor value is (unsigned) NA_INTEGER.
> Definitely transparency would be very useful, and I think a bit in the
> upper byte is a good place to store it.

And if must be (and I remember this correctly), the "magic" 0xffffffff
is only in there to prevent color settings to carry from on page to
the next and breaking the Document Structuring conventions. If so, it
can be replaced with internal driver flags indicating whether there
was a (say) setbg call earlier on the page or not.

   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk)             FAX: (+45) 35327907
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