R/export_svg.R

In rich-iannone/DiagrammeRsvg: Export DiagrammeR Graphviz Graphs as SVG

#' Export grViz graph as SVG with \code{V8}
#' @description Use viz.js with \code{V8} to get the diagram rendered as SVG
#' in R instead of the browser.
#' @param gv htmlwidget to render as SVG.
#' @return \code{string} of SVG XML text.
#' @examples
#' \dontrun{
#'  library(DiagrammeR)
#'  svg <- export_svg(grViz('digraph{a->b; c->a; c->b; c->d;}'))
#'
#'  # this can then be used with htmltools and can save significantly
#'  # on size of output using svg rather than unrendered grViz
#'  library(htmltools)
#'  html_print(HTML(svg))
#' }
#' @importFrom V8 new_context
#' @importFrom utils packageVersion
#' @export export_svg

export_svg <- function(gv){
  
  # Check to make sure that V8 is available
  if(!requireNamespace("V8")) stop("V8 is required to export.",
                                   call. = FALSE)
  
  # Ensure that the minimum version of V8 is 1.0
  stopifnot(packageVersion("V8") >= "0.10")
  
  # Check to make sure gv is grViz
  if(!inherits(gv, "grViz")) "gv must be a grViz htmlwidget."
  
  # Create a new V8 context
  ct <- new_context("window")
  
  # Source the `vis.js` JS library
  invisible(ct$source(system.file("htmlwidgets/lib/viz/viz.js",
                                  package = "DiagrammeR")))
  
  # Create the SVG file
  svg <- 
    invisible(
      ct$call("Viz",
            gv$x$diagram,
            "svg",
            gv$x$config$engine,
            gv$x$config$options))
  
  return(svg)
}