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#' @section Coordinate systems:
#'
#' All `coord_*` functions (like `coord_trans`) return a `Coord*`
#' object (like `CoordTrans`).
#'
#' Each of the `Coord*` objects is a [ggproto()] object,
#' descended from the top-level `Coord`. To create a new type of Coord
#' object, you typically will want to implement one or more of the following:
#'
#' - `aspect`: Returns the desired aspect ratio for the plot.
#' - `labels`: Returns a list containing labels for x and y.
#' - `render_fg`: Renders foreground elements.
#' - `render_bg`: Renders background elements.
#' - `render_axis_h`: Renders the horizontal axes.
#' - `render_axis_v`: Renders the vertical axes.
#' - `backtransform_range(panel_params)`: Extracts the panel range provided
#' in `panel_params` (created by `setup_panel_params()`, see below) and
#' back-transforms to data coordinates. This back-transformation can be needed
#' for coords such as `coord_trans()` where the range in the transformed
#' coordinates differs from the range in the untransformed coordinates. Returns
#' a list of two ranges, `x` and `y`, and these correspond to the variables
#' mapped to the `x` and `y` aesthetics, even for coords such as `coord_flip()`
#' where the `x` aesthetic is shown along the y direction and vice versa.
#' - `range(panel_params)`: Extracts the panel range provided
#' in `panel_params` (created by `setup_panel_params()`, see below) and
#' returns it. Unlike `backtransform_range()`, this function does not perform
#' any back-transformation and instead returns final transformed coordinates. Returns
#' a list of two ranges, `x` and `y`, and these correspond to the variables
#' mapped to the `x` and `y` aesthetics, even for coords such as `coord_flip()`
#' where the `x` aesthetic is shown along the y direction and vice versa.
#' - `transform`: Transforms x and y coordinates.
#' - `distance`: Calculates distance.
#' - `is_linear`: Returns `TRUE` if the coordinate system is
#' linear; `FALSE` otherwise.
#' - `is_free`: Returns `TRUE` if the coordinate system supports free
#' positional scales; `FALSE` otherwise.
#' - `setup_panel_params(scale_x, scale_y, params)`: Determines the appropriate
#' x and y ranges for each panel, and also calculates anything else needed to
#' render the panel and axes, such as tick positions and labels for major
#' and minor ticks. Returns all this information in a named list.
#' - `setup_data(data, params)`: Allows the coordinate system to
#' manipulate the plot data. Should return list of data frames.
#' - `setup_layout(layout, params)`: Allows the coordinate
#' system to manipulate the `layout` data frame which assigns
#' data to panels and scales.
#'
#' @rdname ggplot2-ggproto
#' @format NULL
#' @usage NULL
#' @export
Coord <- ggproto("Coord",
# Is this the default coordinate system?
default = FALSE,
# should drawing be clipped to the extent of the plot panel?
# "on" = yes, "off" = no
clip = "on",
aspect = function(ranges) NULL,
labels = function(labels, panel_params) labels,
render_fg = function(panel_params, theme) element_render(theme, "panel.border"),
render_bg = function(panel_params, theme) {
abort("Not implemented")
},
render_axis_h = function(panel_params, theme) {
abort("Not implemented")
},
render_axis_v = function(panel_params, theme) {
abort("Not implemented")
},
# transform range given in transformed coordinates
# back into range in given in (possibly scale-transformed)
# data coordinates
backtransform_range = function(self, panel_params) {
abort("Not implemented")
},
# return range stored in panel_params
range = function(panel_params) {
abort("Not implemented")
},
setup_panel_params = function(scale_x, scale_y, params = list()) {
list()
},
setup_panel_guides = function(self, panel_params, guides, params = list()) {
panel_params
},
train_panel_guides = function(self, panel_params, layers, default_mapping, params = list()) {
panel_params
},
transform = function(data, range) NULL,
distance = function(x, y, panel_params) NULL,
is_linear = function() FALSE,
# Does the coordinate system support free scaling of axes in a faceted plot?
# Will generally have to return FALSE for coordinate systems that enforce a fixed aspect ratio.
is_free = function() FALSE,
setup_params = function(data) {
list()
},
setup_data = function(data, params = list()) {
data
},
setup_layout = function(layout, params) {
layout
},
# Optionally, modify list of x and y scales in place. Currently
# used as a fudge for CoordFlip and CoordPolar
modify_scales = function(scales_x, scales_y) {
invisible()
}
)
#' Is this object a coordinate system?
#'
#' @export is.Coord
#' @keywords internal
is.Coord <- function(x) inherits(x, "Coord")
# Renders an axis with the correct orientation or zeroGrob if no axis should be
# generated
render_axis <- function(panel_params, axis, scale, position, theme) {
if (axis == "primary") {
draw_axis(panel_params[[paste0(scale, ".major")]], panel_params[[paste0(scale, ".labels")]], position, theme)
} else if (axis == "secondary" && !is.null(panel_params[[paste0(scale, ".sec.major")]])) {
draw_axis(panel_params[[paste0(scale, ".sec.major")]], panel_params[[paste0(scale, ".sec.labels")]], position, theme)
} else {
zeroGrob()
}
}
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