library(ggplot2)
library(pwr)
points <- 1000

n <- 120
d <- 0.2
sig.level <- 0.05

df <- n - 1
tcrit <- qt(1 - sig.level, df = df)
h1ncp <- d * sqrt(n)

h0args <- list(df = df)
h1args <- list(df = df, ncp = h1ncp)

power <- pwr.t.test(d = d, n = n, sig.level = sig.level, alternative = "greater")$power

ggplot() +
  stat_function(fun = dt, args = h0args,
                geom = "area", xlim = c(tcrit, 30),
                fill = "skyblue3", alpha = 0.8) +
  stat_function(fun = dt, args = h1args, n = points,
                geom = "area", xlim = c(-10, tcrit),
                fill = "hotpink2", alpha = 0.4) +
  stat_function(fun = dt, args = h1args, n = points,
                geom = "area", xlim = c(tcrit, 30),
                fill = "seagreen3", alpha = 0.2) +
  geom_function(fun = dt, args = h0args, n = points) +
  geom_function(fun=dt, args = h1args, n = points) +
  geom_vline(xintercept = tcrit, linetype = "dotted") +
  annotate(
    "text",
    x = tcrit + 0.1 , y = I(0.4),
    hjust = "left",
    label = paste0(round(power*100,2), "%"),
    color = "seagreen4"
  ) +
  xlim(-2 * tcrit, 4 * tcrit) +
  theme_linedraw()