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-boun...@r-project.org [mailto:r-help-boun...@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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______________________________________________
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and provide commented, minimal, self-contained, reproducible code.
