Why does mapshot in R (mapview package) not save the addWebGLHeatmap (leaflet extras) layer?

问题

Please help me with the following.

I am making a heatmap using leaflet and addWebGLHeatmap. This works fine, until I try and save the plot as PNG using webshot. See the code below:

m <- map %>% 
  addWebGLHeatmap(data = dataset, lng=~lon, lat=~lat, size = 800, 
  opacity = 0.6, intensity = 1) %>% 
  addPolygons(data = shapefile, weight = 2, color = "black", fillOpacity = 0)

mapshot(m, file = "testRplot.png")

What it shows in plotviewer: Plot in viewer

What it shows after saving: Plot after saving

Hope anyone is able to help.

来源：https://stackoverflow.com/questions/45460035/why-does-mapshot-in-r-mapview-package-not-save-the-addwebglheatmap-leaflet-ex