Save leaflet map in Shiny - r

Question

I have created a leaflet map in a Shiny application. Now I need a download button, so that the user can download the currently shown map including all markers, polygons etc. as a pdf file.
I have found this solution how to save a leaflet map in R: How to save Leaflet in R map as png or jpg file?
But how does it work in Shiny? I kept the example code simple, but think of it, as if there were a lot of changes to the map via leafletProxy() before the user wants to save the map as a pdf.
This is my try, but it's not working.
server.R
library(shiny)
library(leaflet)
library(devtools)
install_github("wch/webshot") # first install phantomjs.exe in your directory
library(htmlwidgets)
library(webshot)
server <- function(input, output){
output$map <- renderLeaflet({
leaflet() %>% addTiles()
})
observe({
if(input$returnpdf == TRUE){
m <- leafletProxy("map")
saveWidget(m, "temp.html", selfcontained = FALSE)
webshot("temp.html", file = "plot.pdf", cliprect = "viewport")
}
})
output$pdflink <- downloadHandler(
filename <- "map.pdf",
content <- function(file) {
file.copy("plot.pdf", file)
}
)
}
ui.R
ui <- fluidPage(
sidebarPanel(
checkboxInput('returnpdf', 'output pdf?', FALSE),
conditionalPanel(
condition = "input.returnpdf == true",
downloadLink('pdflink')
)
),
mainPanel(leafletOutput("map"))
)

Answer 1

I have updated my previous answer to make it more clear and illustrate how to use mapshot from package mapview.
Moreover, following Jake's question below, I noticed that it might be necessary to specify a link to a tile (within addTiles), or the map might be downloaded with a grey background.
Server
server = function(input, output){
mymap <- reactive({
# here I have specified a tile from openstreetmap
leaflet() %>% addTiles('http://{s}.tile.openstreetmap.de/tiles/osmde/{z}/{x}/{y}.png')
})
output$map <- renderLeaflet({
mymap()
})
# function with all the features that we want to add to the map
myfun <- function(map){
addCircles(map,12.5,42,radius=500) %>% addMarkers(12,42,popup="Rome")
}
observe({
leafletProxy("map") %>% myfun()
})
# map that will be downloaded
mapdown <- reactive({
# we need to specify coordinates (and zoom level) that we are currently viewing
bounds <- input$map_bounds
latRng <- range(bounds$north, bounds$south)
lngRng <- range(bounds$east, bounds$west)
mymap() %>% myfun() %>% setView(lng = (lngRng[1]+lngRng[2])/2, lat = (latRng[1]+latRng[2])/2, zoom = input$map_zoom)
})
output$map_down <- downloadHandler(
filename = 'mymap.pdf',
content = function(file) {
# temporarily switch to the temp dir, in case you do not have write
# permission to the current working directory
owd <- setwd(tempdir())
on.exit(setwd(owd))
# using saveWidget and webshot (old)
saveWidget(mapdown(), "temp.html", selfcontained = FALSE)
webshot("temp.html", file = file, cliprect = "viewport")
# using mapshot we can substitute the above two lines of code
# mapshot(mapdown(), file = file, cliprect = "viewport")
}
)
}
UI
ui <- fluidPage(
sidebarPanel(
checkboxInput('returnpdf', 'output pdf?', FALSE),
conditionalPanel(
condition = "input.returnpdf == true",
downloadButton('map_down')
)
),
mainPanel(leafletOutput("map"))
)