Lenka Vraná Lenka Vraná - 1 month ago 13
R Question

How to capture html output as png in R

I use interactive output created by networkD3 package in R. I know how to save the output as html page, but I also need to save the 'static' version of the diagram as .png file.

The code looks like this:

# Load package
library(networkD3)

# Create fake data
src <- c("A", "A", "A", "A", "B", "B", "C", "C", "D")
target <- c("B", "C", "D", "J", "E", "F", "G", "H", "I")
networkData <- data.frame(src, target)

# Plot
simpleNetwork(networkData)


I can save the output by clicking on 'Export' and then 'Save as Image'. However, I prefer to use some commands in my code to save the picture.

Answer

I used function from this page https://github.com/hafen/trelliscope/blob/master/R/thumb.R and tried to simplify it.

You need to have PhantomJS installed from http://phantomjs.org/download.html and the path set in environment variables.

The function looks like this (param p is the html widget, thumbName is the name of new .png file):

library(htmlwidgets)

widgetThumbnail <- function(p, thumbName, width = 1024, height = 768) {
  phantom <- findPhantom()

  success <- FALSE
  if(phantom == "") {
    message("** phantomjs dependency could not be found - thumbnail cannot be generated (run phantomInstall() for details)")
  } else {
    res <- try({
      ff <- paste0(thumbName, ".html")
      ffjs <- paste0(thumbName, ".js")

      # don't want any padding
      p$sizingPolicy$padding <- 0
      suppressMessages(saveWidget(p, ff, selfcontained = FALSE))

      js <- paste0("var page = require('webpage').create();
                    page.viewportSize = { width: ", width,", height: ", height," };
                    page.clipRect = { top: 0, left: 0, width: ", width,", height: ", height," };
                    page.open('", ff, "', function(status) {
                    console.log(\"Status: \" + status);
                    if(status === \"success\") {
                    page.render('", thumbName, ".png');
                    }
                    phantom.exit();
                    });")
      cat(js, file = ffjs)
      system2(phantom, ffjs)
    })
    if(!inherits(res, "try-error")) {
      success <- TRUE
    }
    if(!file.exists(paste0(thumbName, ".png"))) {
      success <- FALSE
    }
  }

  if(!success) {
    message("** could not create htmlwidget thumbnail... creating an empty thumbnail...")
  }
}

#' Get instructions on how to install phantomjs
#' @export
phantomInstall <- function() {
  message("Please visit this page to install phantomjs on your system: http://phantomjs.org/download.html")
}

# similar to webshot
findPhantom <- function() {

  phantom <- Sys.which("phantomjs")

  if(Sys.which("phantomjs") == "") {
    if(identical(.Platform$OS.type, "windows")) {
      phantom <- Sys.which(file.path(Sys.getenv("APPDATA"), "npm", "phantomjs.cmd"))
    }
  }

  phantom

}

It creates .js file, which takes your html widget, captures the screen and saves .js, .html and .png files into active directory:

# Load package
library(networkD3)

# Create fake data
src <- c("A", "A", "A", "A", "B", "B", "C", "C", "D")
target <- c("B", "C", "D", "J", "E", "F", "G", "H", "I")
networkData <- data.frame(src, target)

# Plot
plot = simpleNetwork(networkData)

# Save html as png
widgetThumbnail(p = plot, thumbName = "plot", height = 500)
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