[R] animation without intermediate files?

[Martin Maechler]

>>>>> "MM" == Martin Maechler <maechler at stat.math.ethz.ch>
>>>>>     on Tue, 25 Jan 2005 09:59:03 +0100 writes:

>>>>> "Paul" == Paul Murrell <p.murrell at auckland.ac.nz>
>>>>>     on Tue, 25 Jan 2005 13:40:15 +1300 writes:

    Paul> Hi
    Paul> Cari G Kaufman wrote:
    >>> Hello, 
    >>> 
    >>> Does anyone know how to make "movies" in R by making a
    >>> sequence of plots?  I'd like to animate a long
    >>> trajectory for exploratory purposes only, without
    >>> creating a bunch of image files and then using another
    >>> program to string them together.  In Splus I would do
    >>> this using double.buffer() to eliminate the flickering
    >>> caused by replotting. For instance, with a 2-D
    >>> trajectory in vectors x and y I would use the following:
    >>> 
    >>> motif()
    >>> double.buffer("back")
    >>> for (i in 1:length(x)) {
    >>>   plot(x[i], y[i], xlim=range(x), ylim=range(y))
    >>>   double.buffer("copy")
    >>> }
    >>> double.buffer("front")
    >>> 
    >>> I haven't found an equivalent function to double.buffer in R.  I tried
    >>> playing around with dev.set() and dev.copy() but so far with no success
    >>> (still flickers).

     Paul> Double buffering is only currently an option on the Windows graphics 
     Paul> device (and there it is "on" by default).  So something like ...

     Paul> x <- rnorm(100)
     Paul> for (i in 1:100)
     Paul>     plot(1:i, x[1:i], xlim=c(0, 100), ylim=c(-4, 4), pch=16, cex=2)

     Paul> is already "smooth"

    MM> well, sorry Paul, but not for my definition of "smooth"!

    MM> Instead, 

    MM> n <- 100
    MM> plot(1,1, xlim=c(0,n), ylim=c(-4,4), type="n")
    MM> x <- rnorm(n)
    MM> for (i in 1:n) { points(i, x[i], pch=16, cex=2); Sys.sleep(0.02) }

    MM> comes much closer to my version of "smooth"  ;-)

I apologize to Paul, since  what I said seems to be quite
platform dependent.  Here's my current "knowledge" on the matter:

o  Paul's  " for(..) plot(..) "
    - flickers quite a bit for me {on Linux X11 with no
      particularly fast graphics card}.
    - seems quite smooth for at least two Windows users who have
      relatively fast graphics cards.

o  My solution of
	   " for(..) { points(..) ; Sys.sleep(..) } "
   doesn't redraw the coordinate system and so doesn't "flicker" 
   (afaik, independently of platform)

   HOWEVER on windows; the graphics are somehow buffered and
   points are not drawn one by one, but rather in batches --> "not smooth"


Martin