R-alpha: plot( pch = <character> ) is slow.. -- why ? --

[Thomas Lumley]

On Thu, 3 Jul 1997, Martin Maechler wrote:

> # (The following is using  x11() and an  Ultrasparc I.
> # You should decrease from '20000' if you have a slower machine):
> 
> > x <- runif(20000)
> 
> > for(i in 1:10) print(unix.time(plot(x)))
> [1] 1.66 0.04 3.00 0.00 0.00
> > for(i in 1:10) print(unix.time(plot(x, pch='-')))
> [1]  4.76  3.25 21.00  0.00  0.00
> 
> Why is x11 much faster in drawing pch=1 (a circle), than a simple "-" ?
> Is this X11's `fault' ?

Same thing on a Pentium Pro running Linux and displaying on a Sparcstation
10.  

It looks like X11's fault: the graphics code directly calls the X11
functions in each case, however S-PLUS does not have this slowdown.  I
would have thought the explanation was that "-" requires plotting text and
the circle is just graphics, however the square (pch=0) which is also a
simple graphic is just as slow.

Thomas Lumley
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