Free-form drawing on ggplot2 visualizations using D3

The sketchit function enables flexible, free-form drawing on a ggplot2 visualization. Unlike drawit(), which restricts users to a single continuous line, sketchit() allows multiple lines, color selection, and greater control over drawing behavior. This makes it suitable for exploratory tasks, annotation, or situations where users may wish to sketch multiple patterns or highlight different features of the data.

Usage

sketchit(
  p,
  ...,
  width = NULL,
  height = NULL,
  shiny_message_loc = NULL,
  color_options = TRUE,
  starting_color = NULL,
  palette = NULL,
  stroke_width = 2,
  button_position = c(1, 1),
  max_lines = NULL,
  min_lines = NULL
)

Arguments

p

A ggplot2 object.

...

Additional arguments passed

width

Width of the output widget in pixels.

height

Height of the output widget in pixels.

shiny_message_loc

Name of the Shiny input/output binding used for messaging.

color_options

If TRUE, enables multiple drawing colors.

starting_color

Initial drawing color.

palette

Set of colors available for drawing as a character vector.

stroke_width

Width of the drawn lines.

button_position

Position of the control interface within the plot. Note that this is a numeric vector of length 2, with acceptable values from 0 to 1. c(1,1) is the top right of the graph, and c(0,0) is the bottom left.

max_lines

Maximum number of lines the user can draw.

min_lines

Minimum number of lines required before the user can click "Done".

Value

An r2d3 htmlwidget.

Details

Currently, sketchit can support geom_scatter, geom_line, and geom_smooth.

When color_options = TRUE, the default color pallete is "steelblue", "orange", "green", "red".

If starting_color is updated, the starting_color value will be added to the pallete, assuming it has not been turned off.

If palette is updated, the starting_color will be the first color within the palette.

Shiny Integration

When used within a shiny application, the widget returns the recorded drawing data as a structured object once the user clicks the "Done" button. The recorded user data includes:

• x and y: The coordinates of each point along a drawn line

• color: The color used to draw the line

• line_id: An identifier distinguishing separate lines

• order: The chronological order in which lines were created

The line_id variable groups observations belonging to the same drawn line, while order reflects the historical sequence of drawing actions. Importantly, order is not reset when lines are removed.

For example, if a user draws a blue line, then a red line, removes the red line, and finally draws a green line, the resulting identifiers may be:

• Blue line: line_id = 1, order = 0

• Green line: line_id = 2, order = 2

This behavior preserves the full interaction history and allows downstream reconstruction or analysis of user actions.

Examples

if (FALSE) { # \dontrun{
# Basic usage
p <- ggplot(mtcars, aes(x = wt, y = mpg)) +
  geom_point()

sketchit(p)

# Custom colors and multiple lines
sketchit(
  p,
  color_options = TRUE,
  palette = c("red", "blue", "green"),
  max_lines = 3
)

# Pipe-friendly usage
(ggplot(mtcars, aes(x = wt, y = mpg)) +
  geom_point()) |>
 sketchit(palette = c("red", "blue", "green"),
          max_lines = 3)
} # }