[R] is it possible to fill with a color or transparency gradient?

[hadley wickham]

> I haven't been using R very long, so it's possible that I'm just
> missing something, but I haven't found anything like this in the help
> files.  I've tried to poke around in graphics, grid, and ggplot,
> without any luck so far.  I really like some of the functionality in
> ggplot, and it does some nice things with continuous gradients for the
> color of scatter plot points, for example, but it each individual
> point (or grob) is always one solid color as far as I can tell.

ggplot supports alpha blending provided your graphics device does too
(Quartz on the mac, or pdf version 1.3 or later).  Have a look at the
alpha function for easily making transparent colours, as well as
scgradient for specifying the colour scale.

Oh, I see you want a gradient fill on a polygon - that's a lot harder,
and I can only suggest dividing your polygon up into smaller
rectangles and filling those individually.  That appears to be what
gradient.rect does.

Hadley