Improve Shiny-based `extract_areas()` functionality

[leeper]

Both locate_areas() and extract_areas() use, optionally, a Shiny interface to identify areas. This could probably improved because I'm not much of a Shiny expert. Any advice on improvements and new functionality can be pitched here and/or submitted as PRs.

[jkeuskamp]

I am working on a new Shiny interface for my application of tabulizer::locate_areas. When finished I'll do a pull request.

[jkeuskamp]

to give you an idea, this is what my code currently looks like; suggestions are welcome.

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

  #This script expects to find a variable called thumbnaildir containing the name of the directory containing thumbnails

  thumbnails <-  normalizePath(list.files(thumbnaildir,full.names = TRUE))
  pages <- length(thumbnails)
  Arealist <- vector("list", pages) 
  updateSliderInput(session, "page", max = pages)

  output$image2 <- renderImage({

    return(list(
      src = thumbnails[input$page],
      contentType = "image/png",
      width= paste0(100*input$zoom,"%"),
      height=paste0(100,input$zoom,"%"),
      alt = thumbnails[input$page]
    ))
  }, deleteFile = FALSE)

  xy_range_str <- function(e) {
    if(is.null(e)) return("NULL")
    list=c("top"=round(e$ymin/input$zoom, 1),
           "left"=round(e$xmin/input$zoom, 1),
           "right"=round(e$ymax/input$zoom, 1),
           "bottom"=round(e$ymin/input$zoom, 1))
  }

  output$image_brushinfo <- renderText({
    xy_range_str(input$image_brush)
  })

  update_list <- function(brush) {
    if(!is.null(brush)) Arealist[[input$page]]<<-xy_range_str(brush)
  }

  observe({
    if(input$page > 0) update_list(input$image_brush)
  })

  observe({
    if(input$done > 0){
      update_list(input$image_brush)
      stopApp(Arealist)
    }
  })

}

ui <- fluidPage(
  titlePanel("Image output"),

  fluidRow(
    column(4, 
           wellPanel(
             sliderInput("page", "page :", min = 1, max = 10,
                         value = 1, step = 1),
             sliderInput("zoom", "zoom :", min = 1, max = 3,
                         value = 1, step = .1),
             actionButton("done", "Done")
           ),textOutput("image_brushinfo")),
    column(8, 
           imageOutput("image2",height ="auto", width = "auto",
                       brush = brushOpts(id = "image_brush", 
                                         direction = c("xy"), resetOnNew = TRUE))
    )
  )
)

shinyApp(ui = ui, server = server)

[jkeuskamp]

I placed another incarnation of a potential shiny interface for tabulizer online on www.keuskamp.com. If you want to have a look please mail send me an email so that I can make an account. I am not a Shiny expert at all so I'll need some time to optimize the code, but its getting there