[Rd] Clipping using par(plt=..., xpd=FALSE) inconsistencies

[Paul Murrell]

Hi


Prof Brian Ripley wrote:
> I think you misunderstand what par("plt") is supposed to do.  The 
> documentation says
> 
>       'plt' A vector of the form 'c(x1, x2, y1, y2)' giving the
>            coordinates of the plot region as fractions of the current
>            figure region.
> 
> You haven't subsequently made a new plot, so why do you expect the 
> clipping region to be changed to that you indicated for the next plot?
> 
> I'd say the bug was that box() changed it, and that happens because it 
> internally sets xpd and so resetting xpd sets the clipping region next 
> time it is used.  Because of
> 
> void GClip(pGEDevDesc dd)
> {
>      if (gpptr(dd)->xpd != gpptr(dd)->oldxpd) {
>  	double x1, y1, x2, y2;
>  	setClipRect(&x1, &y1, &x2, &y2, DEVICE, dd);
>  	GESetClip(x1, y1, x2, y2, dd);
>  	gpptr(dd)->oldxpd = gpptr(dd)->xpd;
>      }
> }
> 
> Maybe we should have user-level code to set the clipping region?


I think that would be reasonable.  I added grid.clip() to grid for
situations like this.

Paul


> On Fri, 22 Feb 2008, Greg Snow wrote:
> 
>> Here is a demonstration of behaviour that is probably an optimization by
>> someone far smarter than me that did not anticipate anyone wanting to do
>> this, but for my purposes it looks more like a bug than a feature.
>>
>> I have tested this with R2.6.2 on Windows, no additional packages loaded
>> (beyond the default), I have tested using the default graphics object,
>> pdf, jpeg, and cairoDevice (ok I loaded a package for that) and all show
>> the same behavior.
>>
>> Run the following set of commands:
>>
>> x <- rnorm(1000)
>> hist(x, xlim=c(-4,4))
>>
>> tmp <- par('plt')
>>
>> box(col='#00000000')
>> tmp2 <- tmp
>> tmp2[2] <- tmp2[1] + 0.3
>> par(xpd = FALSE, plt=tmp2)
>> hist(x, col='red', add=TRUE)
>>
>> box(col='#00000000')
>> tmp3 <- tmp
>> tmp3[1] <- tmp3[2] - 0.3
>> par(xpd=FALSE, plt=tmp3)
>> hist(x, col='blue', add=TRUE)
>> par(plt=tmp)
>>
>>
>> This gives me the plot that I want and expect (a histogram with the left
>> section red, the middle white/background, and the right blue).
>>
>> Now comment out or delete the 2 box commands and rerun everything.  The
>> clipping does not happen this time and the final result is a full blue
>> histogram.
>>
>> Is this a bug? Feature? Something else?
>> Does anyone have a better work around than drawing transparent boxes?
>>
>> Thanks,
>>
>>
>>
>>
> 

-- 
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/