Create or write image

If you have nodejs installed, you can use these functions can to create or write images as PNG or SVG, using a vegaspec or vegawidget. To convert to a bitmap, or write a PNG file, you will additionally need the rsvg and png packages.

vw_to_svg(spec, width = NULL, height = NULL, base_url = NULL, seed = NULL)

vw_to_bitmap(spec, scale = 1, width = NULL, height = NULL, ...)

vw_write_svg(spec, path, width = NULL, height = NULL, ...)

vw_write_png(spec, path, scale = 1, width = NULL, height = NULL, ...)

Arguments

spec	An object to be coerced to vegaspec, a Vega/Vega-Lite specification
width	integer, if specified, the total rendered width (in pixels) of the chart - valid only for single-view charts and layered charts; the default is to use the width in the chart specification
height	integer, if specified, the total rendered height (in pixels) of the chart - valid only for single-view charts and layered charts; the default is to use the height in the chart specification
base_url	character, the base URL for a data file, useful for specifying a local directory; defaults to an empty string
seed	integer, the random seed for a Vega specification, defaults to a "random" integer
scale	numeric, useful for specifying larger images supporting the increased-resolution of retina displays
...	additional arguments passed to vw_to_svg()
path	character, local path to which to write the file

Value

vw_to_svg()

character, SVG string

vw_to_bitmap()

array, bitmap array

vw_write_svg()

invisible vegaspec or vegawidget, called for side-effects

vw_write_png()

invisible vegaspec or vegawidget, called for side-effects

Details

There is a known limitation to these functions - if you are using a vegaspec that has dataset loaded from a remote URL. The nodejs scripts are not able to use a proxy, so if your computer uses a proxy to access the remote URL, the data will not load.

These functions can be called using (an object that can be coerced to) a vegaspec.

The nodejs scripts used are adapted from the Vega command line utilities.

See also

vega-view library

Examples

if (FALSE) {
  # requires nodejs to be installed

  # call any of these functions using either a vegaspec or a vegawidget
  vw_to_svg(vegawidget(spec_mtcars))
  vw_to_bitmap(spec_mtcars)
  vw_write_png(spec_mtcars, file.path(tempdir(), "temp.png"))
  vw_write_svg(spec_mtcars, file.path(tempdir(), "temp.svg"))

  # To specify the path to a local file, use base_url
  spec_precip <-
    list(
      `$schema` = vega_schema(),
      data = list(url = "seattle-weather.csv"),
      mark = "tick",
      encoding = list(
        x = list(field = "precipitation", type = "quantitative")
      )
    ) %>%
    as_vegaspec()

  data_dir <- system.file("example-data/", package = "vegawidget")
  vw_write_png(
    spec_precip,
    file.path(tempdir(), "temp-local.png"),
    base_url = data_dir
  )

}