AW: par(par()) corrupts devices (PR#807)

From: "Dr. Jens Oehlschlägel" <jens.oehlschlaegel@bbdo-interone.de>
Date: Mon, 15 Jan 2001 13:58:00 +0100

Dear Prof. Ripley,

I do not insist that features are bugs, so I stop sending this to r-bugs 
and cc r-devel instead

I am replying to this from the archive: I did not actually receive a 

copy.

But it is right to sent bug reports ONLY to r-bugs, isn't it?
I'am actually using a old version of outlook, and some mails from r-help 
appear as attachments, may it's an outlook problem.

This is a feature!

You set par(pin=), and that takes precedence over
par(pty=).  Same with par(plt=).

To unjam it, you need e.g.  par(mai=old.par$mai)

I think that par(pty=) should revert to a default plot spec, and will
change this.  But, the problem with restoring lists like that is that
it depends on exactly the order of the params as they interact.
It is *not* a good idea.  And no.readonly=T does not help as
plt and pin are not readonly.  If the user has resized the device before
restoration, it's pretty chancy what it gets set to.

Thank you for explaining the way it happens. I must admit, that again I am 
baffled things do not work as I expect. WHAT IS THE RECOMMENDED WAY TO 
RESTORE GRAPHICAL PARAMETERS TO EXACTLY WHAT THEY WERE?

I admit, I expected par(par()) not to change anything (I remember vague 
that it worked with the prototype), but in this case it is not (only) a 
problem of restoring a list. Just setting par(pin) and "re-setting" it DOES 
CHANGE the device: subsequent par(pty="s") are ignored.

I am shure I am not the only one who expected the on.exit() stuff within 
the following function to leave the graphical parameters UNCHANGED, but it 
doesn't.

somefunc <- function(){
	oldpin <- par(pin=par("pin"))
	on.exit(par(oldpin))
	plot(1,1)
}

windows(5,3)

par(pty="s")
plot(1,1)
# square
par(pty="m")
plot(1,1)

# which settings do we have before
par1 <- par()

somefunc()

# which settings do we have now
par2 <- par()
# do they differ: yes on plt
all.equal(par1, par2)

# reset plt
par(plt=par1$plt)

# which settings do we have now
par2 <- par()
# do they differ: no
all.equal(par1, par2)

par(pty="s")
plot(1,1)
#still not square
#i.e we have hidden parameters
#because all par() are restored to values where par(pty="s") did work

if the user has resized the device before restoration, it's pretty chancy 

what it gets set to.

I find it frightening to discover that we obvisously have hidden device 
parameters, and more frigthening that they may be modified by resizing.
Sorry that I can't provide code fix, but this is far to deep within the 
heart of R.