Shiny: Export dynamic plot to image?

Question

I am using shiny and I would like to create a download button which stores the current plot as image. this works:

  output$downloadPlot <- downloadHandler(
    filename <- function() {
      paste(input$group,'-top6_plot', Sys.Date(),'.png',sep='') },
    content <- function(file) {
      png(file, width = 980, height = 400, units = "px", pointsize = 12,
          bg = "white", res = NA)

      plot(sin, -pi, 2*pi)

      dev.off()},
    contentType = 'image/png'
  )

But I am using dygraphs for dyanmic plots and this creates an empty white image:

  output$downloadPlot <- downloadHandler(
    filename <- function() {
      paste(input$group,'-top6_plot', Sys.Date(),'.png',sep='') },
    content <- function(file) {
      png(file, width = 980, height = 400, units = "px", pointsize = 12,
          bg = "white", res = NA)

      ReshapedVariables<-variablesForPlot()

      if(input$timeframe == 1){
        Title ="Timeframe: 1 Month"
      } else if(input$timeframe==2){
        Title ="Timeframe: 3 Months"
      } else if(input$timeframe==3){
        Title ="Timeframe: 6 Months"
      } else if(input$timeframe==4){
        Title ="Timeframe: Year to date"
      } else if(input$timeframe==5){
        Title ="Timeframe: 3 Years"
      } else if(input$timeframe==6){
        Title ="Timeframe: All"
      } else {
        Title ="Timeframe: Year to date"
      }

      dygraph(ReshapedVariables, main=Title) %>%
        #dyLegend(width = 200, labelsSeparateLines = TRUE, labelsDiv="VariablePlotLegend", show="always")  %>%
        dyLegend(labelsSeparateLines = FALSE, labelsDiv="VariablePlotLegend", show="always") %>%
        dyOptions(strokeWidth=2, axisLineColor=GRAPH_BLUE, axisLabelColor=GRAPH_BLUE, gridLineWidth=0.1)


      dev.off()},
    contentType = 'image/png'
  )

But the plot code for dygraphs works in general...because in the web shiny app it shows the plot correctly.

Answer 1

This question is rather old, but perhaps this answer may still be useful to you or somebody else. This question is directly related to this question: How to save Leaflet in R map as png or jpg file?. I was having the same problem you are and here is how I solved it for my case:

You'll need to install the packages "htmlwidgets" and "webshot". Then,

library(htmlwidgets)
library(webshot)

You will also need to install PhantomJS. Then,

Save your plot as a separate object on the server side with a generic function call. You'll need to create your variable ReshapedVariables within a separate reactive environment, so it will now be treated as a function:

dyplot <- function(){
dygraph(ReshapedVariables(), main=Title) %>%
labelsDiv="VariablePlotLegend", show="always")  %>%
dyLegend(labelsSeparateLines = FALSE,  labelsDiv="VariablePlotLegend",show="always") %>%
dyOptions(strokeWidth=2, axisLineColor=GRAPH_BLUE, axisLabelColor=GRAPH_BLUE, gridLineWidth=0.1)}

and then the download:

output$downloadData <- downloadHandler(
filename = function () {paste(input$group,'-top6_plot', Sys.Date(),'.png',sep='') },
content = function(file) {
  saveWidget(dyplot(), "temp.html", selfcontained = FALSE)
  webshot("temp.html", file = file)
}
 )