Thanks everyone who replied.

Boris, could you explain a bit more how to obtain this hex-code for a
specific color? Thanks.

Jun


On Wed, May 21, 2014 at 1:37 PM, Boris Steipe <boris.steipe@utoronto.ca>wrote:

> ... I just specify alpha values directly in the hex-code for a color:
>
> set.seed(112352)
> plot(runif(20),runif(20), pch=16)
> polygon(runif(3), runif(3), col="#FF000022")
> polygon(runif(3), runif(3), col="#00FF0022")
> polygon(runif(3), runif(3), col="#0000FF22")
>
> B.
>
>
> On 2014-05-21, at 12:05 PM, William Dunlap wrote:
>
> > You can use adjustcolor() to do some of the arithmetic for you.  E.g.,
> > the following draws red squares with 10 opacities ('alpha's) from 5%
> > to 95%:
> >   plot(1:10)
> >   square <- 0.45 * cbind(c(-1,1,1,-1),c(-1,-1,1,1))
> >   for(i in 1:10) polygon(square+i, col=adjustcolor("red",
> alpha=(i-.5)/10))
> > Bill Dunlap
> > TIBCO Software
> > wdunlap tibco.com
> >
> >
> > On Wed, May 21, 2014 at 8:47 AM, David L Carlson <dcarlson@tamu.edu>
> wrote:
> >> The standard colors in R are opaque, but you can add an alpha value to
> make them semi-transparent. In this example we set alpha halfway between 0
> and 255 to define a semi-transparent red:
> >>
> >>> set.seed(42)
> >>> x <- runif(10)*10
> >>> y <- runif(10)*10
> >>> plot(x, y, pch=16)
> >>> col2rgb("red", alpha=TRUE)
> >>      [,1]
> >> red    255
> >> green    0
> >> blue     0
> >> alpha  255
> >>> redtrans <- rgb(255, 0, 0, 127, maxColorValue=255)
> >>> polygon(c(2, 5, 8), c(2, 10, 2), col=redtrans)
> >>
> >> -------------------------------------
> >> David L Carlson
> >> Department of Anthropology
> >> Texas A&M University
> >> College Station, TX 77840-4352
> >>
> >>
> >>
> >>
> >>
> >> -----Original Message-----
> >> From: r-help-bounces@r-project.org [mailto:r-help-bounces@r-project.org]
> On Behalf Of Jun Shen
> >> Sent: Wednesday, May 21, 2014 10:32 AM
> >> To: R-help
> >> Subject: [R] How to draw a transparent polygon
> >>
> >> Hi everyone,
> >>
> >> How do I draw a transparent ploygon overlaying with a scatter plot?
> >>
> >> Let's say, we call plot() to have a scatter plot, then call polygon() to
> >> add a polygon. I was hoping the polygon can be transparent so the
> scatter
> >> plot is still visible. I can't find any argument in polygon() for such a
> >> feature. Is there another way to do it? Thanks.
> >>
> >> Jun Shen
> >>
> >>        [[alternative HTML version deleted]]
> >>
> >> ______________________________________________
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> >> https://stat.ethz.ch/mailman/listinfo/r-help
> >> PLEASE do read the posting guide
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> >> and provide commented, minimal, self-contained, reproducible code.
> >>
> >> ______________________________________________
> >> R-help@r-project.org mailing list
> >> https://stat.ethz.ch/mailman/listinfo/r-help
> >> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> >> and provide commented, minimal, self-contained, reproducible code.
> >
> > ______________________________________________
> > R-help@r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

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