rasterVis polygon under raster layer in R

Question

I want to plot both a raster layer and a polygon layer using rasterVis::levelplot(), however, I want to have the polygon layer appear under the raster layer.

library(sp)
library(rgeos)
library(raster)
library(rasterVis)

r <- raster(xmn = 0, xmx = 1, ymn = 0, ymx = 1, nrows = 100, ncols = 100,
            crs = "+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs")
r[] <- rnorm(100 * 100)
r[sample(1:ncell(r), ncell(r) / 2)] <- NA

pt <- data.frame(x = 0.5, y = 0.5)
coordinates(pt) <- ~ x + y
proj4string(pt) <- projection(r)
pt_buff <- gBuffer(pt, width = 0.25)
levelplot(r, margin = FALSE) +
  layer(sp.polygons(pt_buff, fill = "grey40", col = NA))

I want the circle under the raster layer:

Answer 1

Use under = TRUE inside the layer function, or the wrapper function layer_:

levelplot(r, margin = FALSE) +
    layer_(sp.polygons(pt_buff,
                      fill = "grey40",
                      col = NA))

Answer 2

You can create custom panel functions in lattice-based plot functions:

levelplot(r, margin = FALSE,
          panel=function(...) {
            sp.polygons(pt_buff, fill = "grey40", col = NA)
            panel.levelplot(...)
          })