[R] PNG diver problem

Peter Dalgaard BSA p.dalgaard at biostat.ku.dk
Thu Nov 29 12:01:25 CET 2001

Don MacQueen <macq at llnl.gov> writes:

> The phrase "relies on X11 calls" makes me wonder...if the machine has
> x11, then whether or not an X11 server running, the libraries are
> there. So perhaps png() could be made to work even so? Far beyond my
> capability, unfortunately.

I believe the problem is that things like font metrics are only known
by the X11 server. Different servers may have different font sets
available. So to write text, programs must ask the X server for the
information. (R has no fonts, only metrics, so we need to rely on
those of either Ghostscript or X11.)

> I, too, would really appreciate having png() [and jpeg()] available
> without also having to have an x11 server running.
> One possibility is Xvfb, which comes with at least one version of
> XFree86. As I understand it, it's intended for just these kinds of
> situations. I believe that "vfb" stands for "virtual frame buffer", so
> that if you have Xvfb running you can point DISPLAY at it and use
> drivers like png() and jpeg() that require a Xserver.

Yes. I believe that is essentially the point of that program. One
issue is that to use it you need to specify a display number that is
not currently in use. If you want an automated procedure, I think
there needs to be a way to get the program to find a new display for
you, and I'm not sure what is a nice way to do that.

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