leaflet slider

app.R

@@ -1,8 +1,12 @@
-library(shiny)
-library(bslib)
+library(shiny)    # for shiny apps
+library(leaflet)  # renderLeaflet function
+library(spData)   # loads the world dataset 
+library(terra)
 library(stars)
-library(tmap)
-library(fs)
+library(leaflet.extras2)
+ui = fluidPage(
+  leafletOutput(outputId = "map")
+)
 
 before_fire_tifs <- fs::dir_ls("before_fire", type="file")[[1]]
 after_fire_tifs <- fs::dir_ls("after_fire", type="file")[[1]]
@@ -11,19 +15,27 @@ after_fire_nbr <- read_stars(after_fire_tifs)
 dnbr <- before_fire_nbr - after_fire_nbr
 
 
-ui <- page_sidebar(
-  theme = bs_theme(bootswatch = "minty"),
-  title = "Map explorer",
-  plotOutput("leaflet")
-)
-
-server <- function(input, output, session) {
-    output$leaflet <- renderPlot(
-    {
-    tmap_mode("plot")  
-    tm_shape(dnbr) + tm_raster()
-    }
-  )
+server = function(input, output) {
+  output$map = renderLeaflet({
+    #https://trafficonese.github.io/leaflet.extras2/reference/addSidebyside.html
+    
+    # addRasterImage options requires pre-release leaflet....
+    stopifnot(compareVersion(as.character(packageVersion("leaflet")), "2.2.1") > 0)
+    
+    Map <- leaflet() |> 
+      addMapPane("right", zIndex = 0) |> 
+      addMapPane("left",  zIndex = 0) |>
+      addTiles(group = "base", layerId = "baseid1", options = pathOptions(pane = "right")) |> 
+      addTiles(group = "base", layerId = "baseid2", options = pathOptions(pane = "left")) |> 
+      addRasterImage(x = rast(after_fire_nbr), options = leafletOptions(pane = "right"), group = "r1") |> 
+      addRasterImage(x = rast(before_fire_nbr), options = leafletOptions(pane = "left"), group = "r2") |> 
+      addLayersControl(overlayGroups = c("r1", "r2")) |>  
+      addSidebyside(layerId = "sidecontrols",
+                    rightId = "baseid1",
+                    leftId  = "baseid2")
+    
+  })
 }
 
 shinyApp(ui, server)
+