used on a smartphone, shiny interactive plot doesn't understand finger movements

Question

I have a R-Shiny application with a plot that implements interactive actions: click, hovering (hovering is passing the mouse over the plot, which can be detected by shiny).

Answer 1

While I can't solve the question completely, maybe a dirty workaround could also have some value to you. Or someone else can build on that answer.

I could reproduce the error that the clicks on the plot are not captured on mobile. But I noticed that I can add additional clickevents with javascript/shinyjs.

One way would be:

  onevent(event = "click", id = "plot", function(e){
    global$clickx = c(global$clickx, e$pageX - 88)
    global$clicky = c(global$clicky, 540 - e$pageY)
  })

It has a few drawbacks:

• shapes are drawn with lines only, it does not capture all hovering on the plot
• the position is quite imprecise since you have to account for borders and margins (very dirty but potential here)

I ran a bit out of time after a few hours, one can for sure improve it, but maybe its of interest for you anyway.

Test here: (link might change within next weeks)

http://ec2-3-121-215-255.eu-central-1.compute.amazonaws.com/shiny/rstudio/sample-apps/mobile/

Reproducible code: (tested on smartphone: Mi A2)

library(shiny)
library(shinyjs)
ui <- fluidPage(
  useShinyjs(),
  h4("Click on plot to start drawing, click again to pause"),

  plotOutput(outputId = "plot", width = "500px", height = "500px")
)


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

  onevent(event = "click", id = "plot", function(e){
    global$clickx = c(global$clickx, e$pageX - 88)
    global$clicky = c(global$clicky, 540 - e$pageY)
  })

  global <- reactiveValues(clickx = NULL, clicky = NULL)

  output$plot= renderPlot({
    plot(x = NULL, y = NULL, xlim=c(0, 440), ylim=c(0, 440), ylab="y", xlab="x", type="l")
    len <- length(global$clickx)
    lines(x = global$clickx, y = global$clicky, type = "p")      
    if(len > 1){
      for(nr in 2:len){
        lines(x = global$clickx[(nr - 1):nr], y = global$clicky[(nr - 1):nr], type = "l")
      }
    }
  })
}
shinyApp(ui, server)