设置多边形的背景色

Question

Is there a way to set the background colour of a polygon? I want to get a plot like this...

set.seed(1)
n <- 100
xx <- c(0:n, n:0)
yy <- c(c(0,cumsum(stats::rnorm(n))), rev(c(0,cumsum(stats::rnorm(n)))))

plot   (xx, yy, type="n", xlab="Time", ylab="Distance")
polygon(xx, yy, angle=45, density=10)
polygon(xx, yy+5, col="white")
polygon(xx, yy+5, angle=45, density=10, col="red")

But ideally without the penultimate line to set the background (I am plotting multiple polygons within a function I am writing). Is there an argument I can use in the final line that will negate the whole of the penultimate line? Cheers.

Answer 1

My answer is 'no' - help(polygon) gives you col for filling the polygon but also uses it for the line shading colour if using angle and density .

This is a relic of the old days when your pen plotter could only pick up one pen at at time...

Doing it twice shouldn't be a problem. Write your own function that takes a polygon and two colour parameters and calls polygon twice.