Draw a trend arrow with confidence interval

Let draw an arrow with its width being dependent on the confidence interval:

drawTrend <- function(x, y, show.circle=TRUE, show.0=TRUE) {

  model <- lm(y ~ x)
  direction.se <- coef(summary(model))["x", "Std. Error"]
  direction <- model$coefficients["x"]
  
library("car")
k <- ellipse(center=c(0.5, 0), radius=c(0.5, 0.5), 
             shape=matrix(data = c(1, 0, 0, 1), nrow=2), 
             segments=1001, draw = FALSE)
par(mar=c(0, 0, 0, 0))
plot(x = c(0, 0), y=c(0, 0), type="n", bty="n", xlim=c(-0.1,1.1), 
     ylim=c(-0.6, 0.6), las=1, asp=1,
     xaxt="n", yaxt="n", xlab="", ylab = "")
if (show.circle) polygon(k[, 1], k[, 2], lwd=1)

maxy <- which.max(k[, 2])
maxx <- which.max(k[, 1])
miny <- which.min(k[, 2])
minx <- which.min(k[, 1])
if (show.circle) {
s <- seq(from=maxy, to=maxx, length.out = 11)
for (pos in 0:10) {
  s_pos <- s[11-pos]
  points(x=k[s_pos,1], y=k[s_pos,2], pch="+")
  text(x=k[s_pos,1]*1.05, y=k[s_pos,2]*1.05, labels=pos)
}
s <- seq(from=miny, to=1001, length.out = 11) 
for (pos in 1:10) {
  s_pos <- s[11-pos]
  points(x=k[s_pos,1], y=k[s_pos,2], pch="+")
  text(x=k[s_pos,1]*1.05, y=k[s_pos,2]*1.05, labels=paste0("-", pos))
}
}

# 0 est égal à 0
# 10 est égal à pi/2


polygon(x=c(0, (0.5+cos((direction-1.96*direction.se)*(pi/2/10))*0.5)*0.8, 
        0.5+cos(direction*(pi/2/10))*0.5, 
        (0.5+cos((direction+1.96*direction.se)*(pi/2/10))*0.5)*0.8, 
        0), 
        y=c(0, (sin((direction-1.96*direction.se)*(pi/2/10))*0.5)*0.8, 
        sin(direction*(pi/2/10))*0.5, 
        (sin((direction+1.96*direction.se)*(pi/2/10))*0.5)*0.8, 
        0), col="lightgrey", border=NA)

lines(x = c(0, 0.5+cos(direction*(pi/2/10))*0.5), y=c(0, sin(direction*(pi/2/10))*0.5), lty=3)

lines(x = c(0, (0.5+cos((direction+1.96*direction.se)*(pi/2/10))*0.5)*1),
      y=c(0, (sin((direction+1.96*direction.se)*(pi/2/10))*0.5)*1), lty=2)
lines(x = c(0, (0.5+cos((direction-1.96*direction.se)*(pi/2/10))*0.5)*1),
      y=c(0, (sin((direction-1.96*direction.se)*(pi/2/10))*0.5)*1), lty=2)
if (show.0) lines(x=c(0, 1), y=c(0,0), lty=3, lwd=2, col="red")
}

Different ways to use it:

layout(mat = matrix(1:4, nrow=2))

# An example with 11 xs of data and a clear trend

x <- 1990:2000

n <- floor(rnorm(n = length(x), mean=100, sd=10))

n <- n + (1:length(x))*5

drawTrend(x, n)

# An example with 11 xs of data and no trend

x <- 1990:2000

n <- floor(rnorm(n = length(x), mean=100, sd=10))

drawTrend(x, n)

# An example with 6 xs of data and no trend

x <- 2000:2005

n <- floor(rnorm(n = length(x), mean=100, sd=10))

drawTrend(x, n)

# An example with 6 xs of data and a trend

x <- 2000:2005

n <- floor(rnorm(n = length(x), mean=100, sd=10))

n <- n - (1:length(x))*5

drawTrend(x, n)

layout(1)

x <- 2000:2005

n <- floor(rnorm(n = length(x), mean=100, sd=10))

n <- n - (1:length(x))*5

drawTrend(x, n, show.circle = FALSE)