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\name{polygon.shadow}
\alias{polygon.shadow}
\title{Display a shadow effect for an arbitrary polygon}
\description{
Displays a shadow effect on an existing plot
}
\usage{
polygon.shadow(x,y=NULL,offset=NA,inflate=NA,col=c("#ffffff","#cccccc"))
}
\arguments{
\item{x,y}{x and y coordinate of the vertices of the polygon. \samp{y}
can be missing if \samp{x} is a list with \samp{x} and \samp{y} components.}
\item{offset}{a vector containing the values of the x and y offsets for the
shadow. Defaults to 1/20 of the maximum x and y dimensions of the polygon.}
\item{col}{the colors of the shadow from the outer edge to the central part.}
\item{inflate}{the amount to "inflate" the shadow relative to the polygon
(i.e. the penumbra). Defaults to the values in \samp{offset}.}
}
\value{nil}
\details{
\samp{polygon.shadow} is typically called just before drawing a polygon.
It displays a shadow effect by drawing the polygon ten times, beginning
with the first color in \samp{col} and stepping through to the second
color to create a "shadow" (or a "halo" if you prefer). Each successive
polygon is shrunk by 10\% of \samp{inflate}. The default shadow effect has
the light at the upper left. This effect may also be used as a text
background.
}
\note{
The background must be a constant color or the shadow effect will not
look right.
}
\author{Jim Lemon}
\seealso{\link{polygon}}
\examples{
par(pty="s")
plot(1:5,type="n",main="Polygon Shadow test",xlab="",ylab="",axes=FALSE)
box()
# do a shadow on a yellow square
polygon(c(1,2.2,2.2,1),c(5,5,3.8,3.8),col="#ffff00")
polygon.shadow(c(1.2,2,2,1.2),c(4.8,4.8,4,4),col=c("#ffff00","#cccc00"))
polygon(c(1.2,2,2,1.2),c(4.8,4.8,4,4),col=c("#ff0000"))
# a green triangle on a light blue square with a big offset
polygon(c(4,5,5,4),c(2,2,1,1),col="#aaaaff")
polygon.shadow(c(4.5,4.8,4.2),c(1.7,1.2,1.2),col=c("#aaaaff","#8888cc"),
offset=c(0.1,-0.1),inflate=c(0.2,0.2))
polygon(c(4.5,4.8,4.2),c(1.7,1.2,1.2),col=c("#00ff00"))
# now a circle as a background
polygon.shadow(cos(seq(0,2*pi,by=pi/20))+3,sin(seq(0,2*pi,by=pi/20))+3,
offset=c(0,0),inflate=c(0.1,0.1))
text(3,3,"Polygon shadow\nas a circular\ntext background",cex=1.5)
}
\keyword{misc}
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