with_custom: Apply a custom filter

In ggfx: Pixel Filters for 'ggplot2' and 'grid'

Apply a custom filter

Description

This function allows you to apply a custom filtering function to a layer. The function must take a nativeRaster object as the first argument along with any other arguments passed to .... Be aware that the raster spans the full device size and not just the viewport currently rendered to. This is because graphics may extend outside of the viewport depending on the clipping settings. You can use get_viewport_area() along with all the other raster helpers provided by ggfx to facilitate working with the input raster. See the example below for some inspiration.

Usage

with_custom(x, filter, ...)

Arguments

x	A ggplot2 layer object, a ggplot, a grob, or a character string naming a filter
filter	A function taking a nativeRaster object as the first argument along with whatever you pass in to ...
...	Additional arguments to filter

Value

Depending on the input, either a grob, Layer, list of Layers, guide, or element object. Assume the output can be used in the same context as the input.

Examples

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
  )

ggplot() +
  with_custom(
    geom_text(aes(0.5, 0.75, label = 'Flippediflop!'), size = 10),
    filter = flip_raster,
    horizontal = FALSE
  )

ggfx documentation built on Aug. 22, 2022, 9:09 a.m.