R devel - Apr 2001 - Re: identify.default ignores any setting of cex (PR#660)

A follow-up to PR#660 (15 Sep 2000) from Brian Ripley:
> R 1.1.1 on Windows, but I think this is widespread.
>
> Using either
>
> par(cex=0.5)
> plot(1:10)
> identify(1:10)
>
> or
> 
> plot(1:10)
> identify(1:10, cex=0.5)
> 
> ignores the cex setting.  The root cause is that par(cex=0.5)
> alters cexbase for the device but sets cex=1.0, and the internal
> text plotting routines use cex and not cexbase.
> 
> The obvious fix is to set cex to cexbase in do_identify. However,
> if this is fixed, there is another problem, The offset of the label
> is related to the cex in use for the label, and not for the symbol.
> So
> 
> plot(1:10, type="n")
> points(1:10, cex=5)
> identify(1:10)
> 
> is not sensible in placing the labels.  That may be hard to anticipate,
> but 
> 
> plot(1:10)
> identify(1:10, cex=0.5)
> 
> needs to use cex=1 not cex=0.5 for the adjustment.  Perhaps identify is
> trying too hard, and should give the user more control over the precise
> position of the label (as S-PLUS does).

The same with 

 par(cex=1); plot(1:10); text(4, 5, "Hello World") # OK
 par(cex=2); plot(1:10); text(4, 5, "Hello World") # OK
 par(cex=2); plot(1:10); text(4, 5, "Hello World", cex = 1) # NOT OK
 par(cex=2); plot(1:10); text(4, 5, "Hello World", cex = 0.5)

So the scaling with cex in text() is relative to the par() settings,
which is not the expected behaviour.


[R-1.2.2 on WinNT 4.0]

Uwe Ligges

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On Wed, 25 Apr 2001 ligges@statistik.uni-dortmund.de wrote:
> A follow-up to PR#660 (15 Sep 2000) from Brian Ripley:
[...]
> The same with
>
>  par(cex=1); plot(1:10); text(4, 5, "Hello World") # OK
>  par(cex=2); plot(1:10); text(4, 5, "Hello World") # OK
>  par(cex=2); plot(1:10); text(4, 5, "Hello World", cex = 1) # NOT
OK
>  par(cex=2); plot(1:10); text(4, 5, "Hello World", cex = 0.5)
>
> So the scaling with cex in text() is relative to the par() settings,
> which is not the expected behaviour.
It is the documented behaviour, though: see the description of cex in
?help.

     cex: numeric character expansion factor; multiplied by
          `par("cex")' yields the final character size.

Brian

-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
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