Drawing a partially transparent density polygon - r

Question

How can I make this red polygon partially transparent so I can see the points underneath it?
library(ks)
set.seed(1234)
x <- runif(1000) + -150
y <- runif(1000) + 20
my.data <- data.frame(x,y)
my.matrix <- as.matrix(my.data)
my_gps_hpi <- Hpi(x = my.matrix, pilot = "samse", pre = "scale")
my.fhat <- kde(x = my.matrix, compute.cont = TRUE, h = my_gps_hpi,
xmin = c(min(my.data$x), min(my.data$y)),
xmax = c(max(my.data$x), max(my.data$y)),
bgridsize = c(100, 100))
my.contours <- c(75)
contourLevels(my.fhat, cont = my.contours)
contourSizes(my.fhat, cont = my.contours, approx = TRUE)
plot(my.data$x, my.data$y)
plot(my.fhat, lwd = 3, display = "filled.contour", cont = my.contours, add = TRUE)
png(file="transparent_polygon_June21_2021.png")
plot(my.data$x, my.data$y)
plot(my.fhat, lwd = 3, display = "filled.contour", cont = my.contours, add = TRUE)
dev.off()

Answer 1

I think I have figured out a solution by digging around in the source code in the file kde.R.
I made several changes to my code.
Changed my.fhat to fhat because the source code might want fhat.
Changed my.contours to contours for the same reason.
Changed contourLevels(my.fhat, cont = my.contours) to hts <- contourLevels(fhat, cont = contours) for the same reason.
Extracted the col.fun from the source code and changed it to return the color of my choice: col.fun <- function(n) {rgb(255, 0, 0, 127, maxColorValue=255)}.
Modified the plot statement to that shown in the code below.
Here is the modified R code:
setwd('C:/Users/mark_/Documents/ctmm/density_in_R/')
set.seed(1234)
library(ks)
x <- runif(1000) + -150
y <- runif(1000) + 20
my.data <- data.frame(x,y)
my.matrix <- as.matrix(my.data)
gps_hpi <- Hpi(x = my.matrix, pilot = "samse", pre = "scale")
fhat <- kde(x = my.matrix, compute.cont = TRUE, h = gps_hpi,
xmin = c(min(my.data$x), min(my.data$y)),
xmax = c(max(my.data$x), max(my.data$y)),
bgridsize = c(100, 100))
contours <- c(75)
hts <- contourLevels(fhat, cont = contours)
contourSizes(fhat, cont = contours, approx = TRUE)
col.fun <- function(n) {rgb(255, 0, 0, 127, maxColorValue=255)}
col.fun(1)
plot(fhat, lwd = 3, display = "filled.contour", cont = contours, col.fun = col.fun(1), drawpoints=TRUE)
png(file="transparent_polygon_June22_2021.png")
plot(fhat, lwd = 3, display = "filled.contour", cont = contours, col.fun = col.fun(1), drawpoints=TRUE)
dev.off()