R help - Sep 2012 - erasing a polygon

I'm updating some (very) old code, and one particular option of its plot
method depends on
a once-was-true trick
     polygon(x, y, border=TRUE, col=0)
     polygon(x, y, border=TRUE, density=0)

would draw the polygon AND erase whatever was underneath it back to background
color.

Is there a reliable way to do this with the current R (standard graphics)?

Terry Therneau

PS For the inquiring, the routine is text.rpart with the fancy=T option, and the
original
target was the postscript driver on Splus 3.4.  (I said it was old.)  The
plot.rpart
routine draws the branches, and text.rpart then wants to lay down some ellipses,
erasing
what is underneath them.

Hi

It seems that it still works.

x<-c(3,7,7,3)
y<-c(4,4,6,6)
par(bg="pink")
plot(1:10,1:10)
polygon(x, y, border=TRUE, col=0)
> version
               _                                                 
platform       i386-pc-mingw32                                   
arch           i386                                              
os             mingw32                                           
system         i386, mingw32                                     
status         Under development (unstable)                      
major          2                                                 
minor          16.0                                              
year           2012                                              
month          03                                                
day            03                                                
svn rev        58569                                             
language       R                                                 
version.string R Under development (unstable) (2012-03-03
r58569)
>
Regards
Petr
> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Terry Therneau
> Sent: Thursday, September 27, 2012 2:37 PM
> To: r-help at r-project.org
> Subject: [R] erasing a polygon
> 
> I'm updating some (very) old code, and one particular option of its
> plot method depends on a once-was-true trick
>      polygon(x, y, border=TRUE, col=0)
>      polygon(x, y, border=TRUE, density=0)
> 
> would draw the polygon AND erase whatever was underneath it back to
> background color.
> 
> Is there a reliable way to do this with the current R (standard
> graphics)?
> 
> Terry Therneau
> 
> PS For the inquiring, the routine is text.rpart with the fancy=T
> option, and the original target was the postscript driver on Splus 3.4.
> (I said it was old.)  The plot.rpart routine draws the branches, and
> text.rpart then wants to lay down some ellipses, erasing what is
> underneath them.
> 
> ______________________________________________
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