app.R

library(shiny)
ui <- fluidPage(
  h4("Click on plot to start drawing, click again to pause. Draw from LEFT to RIGHT"),
  # sliderInput("mywidth", "width of the pencil", min=1, max=30, step=1, value=10),
  plotOutput("plot", width = "800px", height = "500px",
             hover=hoverOpts(id = "hover", delay = 100, delayType = "throttle", clip = TRUE, nullOutside = TRUE),
             click="click"),
  actionButton("reset", "RESET DRAWING"),
  textInput("userid","Write your participant ID"),
  downloadButton("downloadData", "Download data"))

server <- function(input, output, session) {
  vals = reactiveValues(x=NULL, y=NULL)
  draw = reactiveVal(FALSE)
  observeEvent(input$click, handlerExpr = {
    temp <- draw(); draw(!temp)
    if(!draw()) {
      vals$x <- c(vals$x, NA)
      vals$y <- c(vals$y, NA)
    }})
  observeEvent(input$reset, handlerExpr = {
    vals$x <- NULL; vals$y <- NULL
  })
  
  observeEvent(input$hover, {
    if (draw()) {
      vals$x <- c(vals$x, round(input$hover$x))
      vals$y <- c(vals$y, round(input$hover$y))
      
      if (length(vals$x) > 1){
        if (vals$x[length(vals$x)] < max(vals$x)){
          vals$y <- vals$y[vals$x<=vals$x[length(vals$x)]]
          vals$x <- vals$x[vals$x<=vals$x[length(vals$x)]]
        }
        
        vals$y <- rev(rev(vals$y)[!duplicated(rev(vals$x))])
        vals$x <- rev(rev(vals$x)[!duplicated(rev(vals$x))])
      }
    }})
  
  output$plot= renderPlot({
    plot(x=vals$x, y=vals$y, xlim=c(0, 100), ylim=c(0, 100), ylab="Amount", xlab="Year", type="l", lwd=2, xaxt="n")
    axis(1, at = seq(0,100,by=5), las=2)
  })
  
  output$downloadData <- downloadHandler(
    filename = function() {
      paste0("data-",input$userid, format(Sys.time(), format = "%Y-%m-%d--%H-%M-%S"), ".csv", sep="")
    },
    content = function(file) {
      # Make data frame:
      df <- expand.grid(
        id = input$userid,
        time = Sys.time(),
        x = 0:100,
        y = NA
      )
      y <- vals$y[match(df$x,vals$x)]
      df$y <- round(approx(df$x[!is.na(y)],y[!is.na(y)],xout=df$x)$y,2)
      write.csv(df, file)
    }
  )
  
  }

shinyApp(ui, server)