[R] erasing a polygon

[Terry Therneau]

I was able to puzzle it out with the help of the book "R Graphics" (Murrell).
When par("bg") = "transparenent" one needs to use col="white", otherwise the
old code col=0 works correctly.

The default for pdf and x11, the two I use, is transparent.

Terry Therneau



On 09/27/2012 08:48 AM, PIKAL Petr wrote:
> 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)
>
>> 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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