Dual-Tone Regression Line with Contrast-Aware Strokes

Source: R/geom_lm_dual.R

Draws a regression line with perceptually distinct dual-stroke coloring for improved visibility.

geom_lm_dual(
  data,
  mapping,
  method = "lm",
  formula = y ~ x,
  base_color = "#777777",
  contrast = 4.5,
  method_contrast = "WCAG",
  ...,
  linewidth = 1,
  show.legend = NA
)

Arguments

data

A data frame containing the variables.

mapping

Aesthetic mapping, must include x and y.

method

Regression method to use (default is "lm").

formula

Model formula (default is y ~ x).

base_color

Base color to derive the dual-tone pair from.

contrast

Minimum contrast ratio to aim for (default is 4.5).

method_contrast

Contrast algorithm to use ("WCAG", "APCA", or "auto").

...

Additional parameters passed to geom_segment_dual().

linewidth

Width of the line stroke (top stroke). Bottom stroke is drawn slightly thicker.

show.legend

Whether to show legend.

Value

A ggplot2 layer containing the dual-stroke regression line.

Examples

library(ggplot2)

# Simple test with linear trend
set.seed(42)
df <- data.frame(x = 1:100, y = 0.5 * (1:100) + rnorm(100))
ggplot(df, aes(x, y)) +
  geom_point() +
  geom_lm_dual(data = df, mapping = aes(x = x, y = y)) +
  theme_minimal()


# Over grayscale tiles
x <- seq(1, 11, length.out = 100)
y <- 0.5 * x + rnorm(100, 0, 0.3)
df1 <- data.frame(x = x, y = y)

# Tile fill definitions
fill_colors <- data.frame(
  x = 1:11,
  fill = c("#000000", "#1b1b1b", "#444444", "#777777", "#aaaaaa",
           "#dddddd", "#D5D5D5", "#E5E5E5", "#F5F5F5", "#FAFAFA", "#FFFFFF")
)

# Expand tile grid and join with fill colors
tiles <- expand.grid(x = 1:11, y = seq(0, 1, length.out = 100)) |>
  merge(fill_colors, by = "x")

ggplot() +
  geom_tile(
    data = tiles, aes(x = x, y = y, fill = fill),
    width = 1, height = 10
  ) +
  scale_fill_identity() +
  geom_point(
    data = df1, aes(x = x, y = y),
    colour = "purple", size = 2
  ) +
  ## Uncomment to use points with frames:
  # geom_point(
  #   data = df1, aes(x = x, y = y),
  #   shape = 21, colour = "white", fill = "black", size = 3
  # ) +
  geom_lm_dual(
    data = df1, mapping = aes(x = x, y = y),
    linewidth = 2
  ) +
  coord_fixed() +
  theme_minimal()