Controlling the sketch

Every sketch geom shares four parameters that shape the hand-drawn look: roughness, bowing, n_passes, and seed. They are layer parameters (not aesthetics), so you pass them to the geom_sketch_*() call.

roughness

How far points are displaced. 0 is ruler-straight; the default is 1; values above ~3 get loose and scribbly.

x  <- seq(0, 10, length.out = 50)
d  <- data.frame(x = x, y = sin(x))

ggplot(d, aes(x, y)) +
  geom_sketch_line(aes(colour = "0.0  (straight)"), roughness = 0,   seed = 2) +
  geom_sketch_line(aes(colour = "1.0  (default)"),  roughness = 1,   seed = 2) +
  geom_sketch_line(aes(colour = "2.5"),             roughness = 2.5, seed = 2) +
  geom_sketch_line(aes(colour = "5.0  (loose)"),    roughness = 5,   seed = 2) +
  scale_colour_brewer("roughness", palette = "Set1") +
  labs(title = "The roughness dial") +
  theme_sketch()

On bars:

df <- data.frame(x = c("A", "B", "C"), y = c(4, 6, 3))
for (r in c(0, 1, 3)) {
  print(
    ggplot(df, aes(x, y)) +
      geom_sketch_col(fill = "#7BAFD4", roughness = r, seed = 1L) +
      labs(subtitle = paste("roughness =", r), x = NULL) +
      theme_sketch(base_size = 9)
  )
}

bowing

How much line segments bow (curve) between their endpoints. Higher values give a springier, more relaxed stroke.

seg <- data.frame(x = 1, y = 1, xend = 6, yend = 4)
for (b in c(0, 2, 5)) {
  print(
    ggplot(seg) +
      geom_sketch_segment(aes(x = x, y = y, xend = xend, yend = yend),
                          bowing = b, roughness = 0.6, linewidth = 1,
                          seed = 7L) +
      labs(subtitle = paste("bowing =", b)) +
      theme_sketch(base_size = 9)
  )
}

n_passes

How many overlaid strokes to draw. 2 (the default) gives the classic “double-stroke” sketch look; 1 is a single pass; 3+ looks heavily worked.

for (n in c(1, 2, 4)) {
  print(
    ggplot(d, aes(x, y)) +
      geom_sketch_line(n_passes = n, roughness = 1.5, linewidth = 0.7,
                       colour = "grey20", seed = 3L) +
      labs(subtitle = paste("n_passes =", n)) +
      theme_sketch(base_size = 9)
  )
}

seed — reproducible wobble

The sketch is random, but seeded. A given seed always produces the same drawing, so figures are reproducible across renders and devices. Change the seed for a fresh “hand”.

d2 <- data.frame(x = 1:8, y = c(2, 5, 3, 8, 6, 9, 7, 10))
for (s in c(1, 1, 42)) {
  print(
    ggplot(d2, aes(x, y)) +
      geom_sketch_line(linewidth = 1, seed = s) +
      geom_sketch_point(size = 3, seed = s + 100) +
      labs(subtitle = paste("seed =", s)) +
      theme_sketch(base_size = 9)
  )
}

The first two panels are identical (same seed); the third differs.

Session-wide default

If you do not pass seed, geoms use getOption("ggsketch.seed", 1L). Set it once to make a whole document reproducible:

options(ggsketch.seed = 1L)

ggsketch never touches your global random state: each randomized routine draws from its own seeded stream and restores .Random.seed afterward, so it will not interfere with set.seed() elsewhere in your analysis.