[R] Simple graphics

[Alberto Vieira Ferreira Monteiro]

Is there any way that I can do something like this:

  png("file.png", width=200, height=200)
  polygon(c(50, 50, 150, 150), c(50, 150, 150, 50))
  dev.off()

and then have a png file with a 100 x 100 pixels rectangle in the middle 
of it? It seems that when I call "plot", it redefines the image coordinates
to some "optimized" value and then I lose any information to draw
exactly what I want.

Alberto Monteiro