render_context | R Documentation |
These utility functions can help when creating custom filters (using
with_custom()
) as they can provide information about the current rendering
context.
viewport_location()
index_raster(raster, cols, rows)
get_raster_area(raster, xmin, ymin, xmax, ymax)
set_raster_area(raster, value, xmin, ymin)
get_viewport_area(raster)
set_viewport_area(raster, value)
viewport_is_clipping()
current_resolution()
to_pixels(x, y_axis = FALSE, location = FALSE)
from_pixels(x)
raster |
A |
cols , rows |
Column and row indices |
xmin , ymin , xmax , ymax |
Boundaries of the area in pixels. {0,0} is the top-left corner |
value |
An object of the same type as |
x |
A numeric or unit object |
y_axis |
is the unit pertaining to the y-axis? Defaults to |
location |
is the unit encoding a location? Defaults to |
viewport_location()
: Returns the bounding box defining the current
viewport in pixels in the order xmin
, ymin
, xmax
, ymax
index_raster()
: Is a version of the classic [,]
indexing that is aware
of the row-major order of rasters
get_raster_area()
: Extracts an area of a raster based on a bounding box
set_raster_area()
: Sets an area of a raster to a new raster value
get_viewport_area()
: A version of get_raster_area()
that specifically
extract the area defined by the current viewport
set_viewport_area()
: A version of set_raster_area()
that specifically
sets the area defined by the current viewport
viewport_is_clipping()
: Returns TRUE
if the current viewport has
clipping turned on
current_resolution()
: Returns the resolution of the active device in ppi
(pixels-per-inch)
to_pixels(x)
: Converts x
to pixels if x
is given as a unit object. It
is assumed that x encodes a dimension and not a location. If x
is a
numeric it is assumed to already be in pixels
from_pixels
: Converts a numeric giving some pixel dimension to a unit
object.
Depends on the function - see details.
# These functions are intended to be used inside filter functions, e.g.
library(ggplot2)
flip_raster <- function(raster, horizontal = TRUE) {
# Get the viewport area of the raster
vp <- get_viewport_area(raster)
# Get the columns and rows of the raster - reverse order depending on
# the value of horizontal
dims <- dim(vp)
rows <- seq_len(dims[1])
cols <- seq_len(dims[2])
if (horizontal) {
cols <- rev(cols)
} else {
rows <- rev(rows)
}
# change the order of columns or rows in the viewport raster
vp <- index_raster(vp, cols, rows)
# Assign the modified viewport back
set_viewport_area(raster, vp)
}
ggplot() +
with_custom(
geom_text(aes(0.5, 0.75, label = 'Flippediflop!'), size = 10),
filter = flip_raster,
horizontal = TRUE
)
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