Can you apply a progress bar from waitress to a modal Dialog?

Question

In a shiny app, I have a plot which sometimes takes a bit of time to calculate. I would like to show the progress of this calculation with a progressbar from the waiter package. Is there a way to apply a waitress to a modalDialog? Below is a MWE where the waitress is applied to the full page, but I would find it way better if I just had one bar on the modalDialog.

I have checked the possibilities from the Demo: Applying it to the actionButton does not work in my actual app. Showing it as a notification would work, but I am not aware of any way to display the notification in the center of the screen rather than in a corner. I guess the "on elements" is what I am looking for, but my modalDialog does not have an input or output id.

library(shiny)
library(shinipsum)
library(waiter)
library(plotly)

complicated_function <- function(){
  waitress <- Waitress$new(theme = "overlay",min = 0,max = 20)
  for(i in 1:20){
    waitress$inc(1)
    Sys.sleep(0.2)
  }
  waitress$close()
  return(random_ggplotly())
}

ui <- fluidPage(
  useWaitress(),
  actionButton("plotButton", "Generate Plot")
)

server <- function(input,output,session){
  modal1 <- modalDialog(
    renderPlotly({
      complicated_function()
    })
  )
  observeEvent(input$plotButton,{
    showModal(modal1)
  })
}
shinyApp(ui, server)

Answer 1

You can try the attendantBar from the same package:

library(shiny)
library(shinipsum)
library(waiter)
library(plotly)

complicated_function <- function(){
  att <- Attendant$new("progress-bar", hide_on_max = TRUE)
  for(i in 1:20){
    att$set(i * 10)
    Sys.sleep(0.2)
   }
  return(random_ggplotly())
}


ui <- fluidPage(
  useAttendant(),
  
  actionButton("plotButton", "Generate Plot")
)

server <- function(input,output,session){
  
  
  modal1 <- modalDialog(
    attendantBar("progress-bar"),
    renderPlotly({

      complicated_function()
    })
    
  )
  observeEvent(input$plotButton,{
    showModal(modal1)
    
  })
}
shinyApp(ui, server)