geom_bezier: Create quadratic or cubic bezier curves
In YTLogos/ggforce: Accelerating 'ggplot2'

Description Usage Arguments Details Aesthetics Computed variables Author(s) Examples

This set of geoms makes it possible to connect points creating either quadratic or cubic beziers. bezier and bezier2 both work by calculating points along the bezier and connecting these to draw the curve. bezier0 directly draws the bezier using bezierGrob and is thus probably more performant. In line with the geom_link() and geom_link2() differences geom_bezier creates the points, assign an index to each interpolated point and repeat the aesthetics for the start point, while geom_bezier2 interpolates the aesthetics between the start and end points.

stat_bezier(mapping = NULL, data = NULL, geom = "path",
  position = "identity", na.rm = FALSE, show.legend = NA, n = 100,
  inherit.aes = TRUE, ...)

geom_bezier(mapping = NULL, data = NULL, stat = "bezier",
  position = "identity", arrow = NULL, lineend = "butt", na.rm = FALSE,
  show.legend = NA, inherit.aes = TRUE, n = 100, ...)

stat_bezier2(mapping = NULL, data = NULL, geom = "path_interpolate",
  position = "identity", na.rm = FALSE, show.legend = NA, n = 100,
  inherit.aes = TRUE, ...)

geom_bezier2(mapping = NULL, data = NULL, stat = "bezier2",
  position = "identity", arrow = NULL, lineend = "butt", na.rm = FALSE,
  show.legend = NA, inherit.aes = TRUE, n = 100, ...)

stat_bezier0(mapping = NULL, data = NULL, geom = "bezier0",
  position = "identity", na.rm = FALSE, show.legend = NA,
  inherit.aes = TRUE, ...)

geom_bezier0(mapping = NULL, data = NULL, stat = "bezier0",
  position = "identity", arrow = NULL, lineend = "butt", na.rm = FALSE,
  show.legend = NA, inherit.aes = TRUE, ...)

`mapping`	Set of aesthetic mappings created by `aes()` or `aes_()`. If specified and `inherit.aes = TRUE` (the default), it is combined with the default mapping at the top level of the plot. You must supply `mapping` if there is no plot mapping.
`data`	The data to be displayed in this layer. There are three options: If `NULL`, the default, the data is inherited from the plot data as specified in the call to `ggplot()`. A `data.frame`, or other object, will override the plot data. All objects will be fortified to produce a data frame. See `fortify()` for which variables will be created. A `function` will be called with a single argument, the plot data. The return value must be a `data.frame.`, and will be used as the layer data.
`geom`	The geometric object to use display the data
`position`	Position adjustment, either as a string, or the result of a call to a position adjustment function.
`na.rm`	If `FALSE`, the default, missing values are removed with a warning. If `TRUE`, missing values are silently removed.
`show.legend`	logical. Should this layer be included in the legends? `NA`, the default, includes if any aesthetics are mapped. `FALSE` never includes, and `TRUE` always includes. It can also be a named logical vector to finely select the aesthetics to display.
`n`	The number of points to create for each segment
`inherit.aes`	If `FALSE`, overrides the default aesthetics, rather than combining with them. This is most useful for helper functions that define both data and aesthetics and shouldn't inherit behaviour from the default plot specification, e.g. `borders()`.
`...`	other arguments passed on to `layer()`. These are often aesthetics, used to set an aesthetic to a fixed value, like `color = "red"` or `size = 3`. They may also be parameters to the paired geom/stat.
`stat`	The statistical transformation to use on the data for this layer, as a string.
`arrow`	Arrow specification, as created by `grid::arrow()`
`lineend`	Line end style (round, butt, square)

Input data is understood as a sequence of data points the first being the start point, then followed by one or two control points and then the end point. More than 4 and less than 3 points per group will throw an error. grid::bezierGrob() only takes cubic beziers so if three points are supplied the middle one as duplicated. This, along with the fact that grid::bezierGrob() estimates the curve using an x-spline means that the curves produced by geom_bezier and geom_bezier2 deviates from those produced by geom_bezier0. If you want true bezier paths use geom_bezier or geom_bezier2.

geom_link, geom_link2 and geom_lin0 understand the following aesthetics (required aesthetics are in bold):

x
y
color
size
linetype
alpha
lineend

x, y: The interpolated point coordinates
index: The progression along the interpolation mapped between 0 and 1

Thomas Lin Pedersen

beziers <- data.frame(
    x = c(1, 2, 3, 4, 4, 6, 6),
    y = c(0, 2, 0, 0, 2, 2, 0),
    type = rep(c('cubic', 'quadratic'), c(3, 4)),
    point = c('end', 'control', 'end', 'end', 'control', 'control', 'end')
)
help_lines <- data.frame(
    x = c(1, 3, 4, 6),
    xend = c(2, 2, 4, 6),
    y = 0,
    yend = 2
)
ggplot() + geom_segment(aes(x = x, xend = xend, y = y, yend = yend),
                        data = help_lines,
                        arrow = arrow(length = unit(c(0, 0, 0.5, 0.5), 'cm')),
                        colour = 'grey') +
    geom_bezier(aes(x= x, y = y, group = type, linetype = type),
                data = beziers) +
    geom_point(aes(x = x, y = y, colour = point), data = beziers)