如何在Shiny中保存具有绘制形状/点的传单地图？

Question

This question is a follow-up to the questions How to save a leaflet map in Shiny , and Save leaflet map in Shiny .

I add a toolbar to draw shapes/points on the map that is addDrawToolbar in the leaflet.extras package. That lets users to draw lines, shapes, ... interactively. In the end I want one to be able to save the map with the drawn shapes as a pdf or png.

I have coded up the following making use of the answer to the question: How to save a leaflet map in Shiny . But it does not help achieve my goal.

Is there anyone who can help me?

library(shiny)
library(leaflet)
library(leaflet.extras)
library(mapview)


ui <- fluidPage(

    leafletOutput("map"),
    br(),
    downloadButton("download_pdf", "Download .pdf")
)

server <- function(input, output, session) {


     foundational_map <- reactive({

        leaflet() %>% 

          addTiles()%>%

          addMeasure(
              primaryLengthUnit = "kilometers",
              secondaryAreaUnit = FALSE
           )%>%

          addDrawToolbar(
               targetGroup='draw',

               editOptions = editToolbarOptions(selectedPathOptions = 
                                       selectedPathOptions()),

                polylineOptions = filterNULL(list(shapeOptions = 
                                        drawShapeOptions(lineJoin = "round", 
                                        weight = 3))),

                circleOptions = filterNULL(list(shapeOptions = 
                                      drawShapeOptions(),
                                      repeatMode = F,
                                      showRadius = T,
                                      metric = T,
                                      feet = F,
                                      nautic = F))) %>%
           setView(lat = 45, lng = 9, zoom = 3) %>%
           addStyleEditor(position = "bottomleft", 
                 openOnLeafletDraw = TRUE)
 })


 output$map <- renderLeaflet({

         foundational_map()
                    })


 user_created_map <- reactive({

           foundational_map() %>%

            setView(lng = input$map_center$lng, lat = input$map_center$lat, 
                           zoom = input$map_zoom)
             })


 output$download_pdf <- downloadHandler(

         filename = paste0("map_", Sys.time(), ".pdf"),

         content = function(file) {
                 mapshot(user_created_map(), file = file)
  }
 )



 }

 shinyApp(ui = ui, server = server)

Answer 1

Apparently the mapshot function is not aware of drawn polygons and just stores the clean leaflet-map, as it launches an isolated background process which captures the webshot.

I would propose this workaround, which captures the whole screen (using this batch -file) and saves it as png . ( only for Windows )

This is not very beautiful as it will also capture the windows and browser menu bars, although that could be adapted in the batch-file.

The batch-file must be in the same directory and must be named screenCapture.bat .

library(shiny)
library(leaflet)
library(leaflet.extras)
library(mapview)

ui <- fluidPage(
  leafletOutput("map"),
  actionButton("download_pdf", "Download .pdf")
)

server <- function(input, output, session) {
  foundational_map <- reactive({
    leaflet() %>%
      addTiles()%>%
      addMeasure(
        primaryLengthUnit = "kilometers",
        secondaryAreaUnit = FALSE
      )%>%
      addDrawToolbar(
        targetGroup='draw',
        editOptions = editToolbarOptions(selectedPathOptions = 
                                           selectedPathOptions()),
        polylineOptions = filterNULL(list(shapeOptions = 
                                            drawShapeOptions(lineJoin = "round", 
                                                             weight = 3))),
        circleOptions = filterNULL(list(shapeOptions = 
                                          drawShapeOptions(),
                                        repeatMode = F,
                                        showRadius = T,
                                        metric = T,
                                        feet = F,
                                        nautic = F))) %>%
      setView(lat = 45, lng = 9, zoom = 3) %>%
      addStyleEditor(position = "bottomleft", 
                     openOnLeafletDraw = TRUE)
  })
  output$map <- renderLeaflet({
    foundational_map()
  })
  user_created_map <- reactive({
    foundational_map()
  })

  ## observeEvent which makes a call to the Batch-file and saves the image as .png
  observeEvent(input$download_pdf, {
    img = paste0("screen", runif(1,0,1000), ".png")
    str = paste('call screenCapture ', img)
    shell(str)
  })

}

shinyApp(ui = ui, server = server)

To remove the browser and Windows toolbar , I manipulated the .bat-file like this:

Line 66:

int height = windowRect.bottom - windowRect.top - 37;

Line 75:

GDI32.BitBlt(hdcDest, 0, -80, width, height, hdcSrc, 0, 0, GDI32.SRCCOPY);

This works on my machine, but you will have to adapt the values or even come up with a better solution, since I have to admit that I'm not too good at batch scripting. This will hide the toolbars, but there will be a black strip at the bottom.