R help - Oct 2006 - savePlot and dev.copy

Dear R gurus,

R 2.4.0 under Windows XP.

We have developed several dozen R functions to make and save
specialized plots.  These use savePlot() to optionally save the
plot to files (eps, jpg, png, ...).

The thought has come up of putting the functions into an R
package.  Because savePlot is available only on Windows, we
would instead detect the OS and use dev.copy in place of
savePlot when not running under Windows.

My question is, if this code is rewritten anyway, what are the
pros and cons of using dev.copy under *all* operating systems
vs. using savePlot on Windows and dev.copy on other platforms?

Thanks!

-- 
Mike Prager, NOAA, Beaufort, NC
* Opinions expressed are personal and not represented otherwise.
* Any use of tradenames does not constitute a NOAA endorsement.

Hi


Mike Prager wrote:
> Dear R gurus,
> 
> R 2.4.0 under Windows XP.
> 
> We have developed several dozen R functions to make and save
> specialized plots.  These use savePlot() to optionally save the
> plot to files (eps, jpg, png, ...).
> 
> The thought has come up of putting the functions into an R
> package.  Because savePlot is available only on Windows, we
> would instead detect the OS and use dev.copy in place of
> savePlot when not running under Windows.
> 
> My question is, if this code is rewritten anyway, what are the
> pros and cons of using dev.copy under *all* operating systems
> vs. using savePlot on Windows and dev.copy on other platforms?

The underlying mechanisms of dev.copy() and savePlot() are identical --
copy the display list from one device to another -- but savePlot() has
some niceties wrapped around the outside.

These boil down to making the copy the same size as the original.  If
you use dev.copy() naively, you can get a copy which is a very different
size from the original.  The function dev.print() does a bit better in
terms of retaining the original size, but there is trouble when you copy
from a device for which the size is specified in inches [like windows(),
x11(), postscript() and pdf()] to a device for which the size is in
pixels [png(), jpeg(), bitmap()].

savePlot() handles all of the sizing problems for you (but only works on
Windows).  dev.copy() works everywhere, but you would have to do a bit
of mucking about yourself to get around the sizing problems -- see the
source for dev.print() for a starting point.

The authors of the Windows device might have more to say.

Paul
-- 
Dr Paul Murrell
Department of Statistics
The University of Auckland
Private Bag 92019
Auckland
New Zealand
64 9 3737599 x85392
paul at stat.auckland.ac.nz
http://www.stat.auckland.ac.nz/~paul/