[Rd] readPNG gives warnings and doesn't execute sample code from help files

[Ben Bolker]

Joris Meys <jorismeys <at> gmail.com> writes:

> 
> I believed the standard plotting device on R in 2.12.1 would support
> per-pixel alpha. It does support alpha, as
> 
>  plot(1:2,type="l")
>  polygon(c(1,1,2,2),c(1,2,2,1),col=rgb(60,100,60,60,maxColorValue=255))
> 
> plots correctly. Which device should I use then?

See 

http://developer.r-project.org/Raster/raster-RFC.html

(near the bottom of the page, where it explains that the
Windows device supports alpha but not per-pixel alpha ...)

 cheers
    Ben Bolker