Displays a shadow effect on an existing plot
polygon.shadow(x,y=NULL,offset=NA,inflate=NA,col=c("#ffffff","#cccccc"))x and y coordinate of the vertices of the polygon. y can be missing if x is a list with x and y components.
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.
the colors of the shadow from the outer edge to the central part.
the amount to "inflate" the shadow relative to the polygon (i.e. the penumbra). Defaults to the values in offset.
nil
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 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 inflate. The default shadow effect has the light at the upper left. This effect may also be used as a text background.
# NOT RUN {
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)
# }
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