leaflet plugin and leafletProxy with polylineDecorator as Example - r

Question

Please refer also to a question leaflet plugin and leafletProxy.
I want to use polylineDecorator Plugin in leaflet for R.
Following instruction for how to use leaflet plugin from R, I can use it if I use the approach togeher with leaflet(). See the first example, which works as i wanted. But if i try to use the same approach with leafletProxy(), it just doesn't do anything I only get line without decorator. See the second example.
My question is how I can use leaflet plugin with R's leafletProxy().
Example 1: Version that works, not using the lefletProxy.
library(shiny)
library(leaflet)
library(htmltools)
download.file(
'https://raw.githubusercontent.com/bbecquet/Leaflet.PolylineDecorator/master/dist/leaflet.polylineDecorator.js',
'leaflet.polylineDecorator.js')
polylineDecoratorPlugin <- htmlDependency('Leaflet.PolylineDecorator',
'1.6.0',
src = normalizePath('.'),
script = 'leaflet.polylineDecorator.js')
registerPlugin <- function(map, plugin) {
map$dependencies <- c(map$dependencies, list(plugin))
map
}
ui <- bootstrapPage(
tags$style(type = "text/css", "html, body {width:100%;height:100%}"),
leafletOutput("map", width = "100%", height = "100%")
)
server <- function(input, output) {
dat <- data.frame(lat0=c(29,29.1),lat1=c(30,30.1), lng0=c(-96,-96.1),lng1=c(-95,-95.1))
output$map <- renderLeaflet({
m <- leaflet() %>%
# addProviderTiles(providers$OpenStreetMap.BlackAndWhite) %>%
setView(lat=29.762778, lng=-95.383056, zoom=8) %>% # Houston
registerPlugin(polylineDecoratorPlugin) %>%
addPolylines(lat=c(dat$lat0[1], dat$lat1[1]), lng=c(dat$lng0[1],dat$lng1[1])) %>%
addPolylines(lat=c(dat$lat0[2], dat$lat1[2]), lng=c(dat$lng0[2],dat$lng1[2])) %>%
htmlwidgets::onRender("function(el,x,data) {
for(var i=0; i < data.lat0.length; i++) {
var dec = L.polylineDecorator([[data.lat0[i],data.lng0[i]],[data.lat1[i],data.lng1[i]]], {
patterns: [
{offset: 0, repeat: 20, symbol: L.Symbol.arrowHead({pixelSize:15, pathOptions:{stroke:true}})}
]
}).addTo(this);
}
}",
data=dat)
})
}
# Run the application
shinyApp(ui = ui, server = server)
Here's what I get from the code above, and this is what I expected.
Example 2: Version that does not show the decorator, just line, using lefletProxy():
library(shiny)
library(leaflet)
library(htmltools)
download.file(
'https://raw.githubusercontent.com/bbecquet/Leaflet.PolylineDecorator/master/dist/leaflet.polylineDecorator.js',
'leaflet.polylineDecorator.js')
polylineDecoratorPlugin <- htmlDependency('Leaflet.PolylineDecorator',
'1.6.0',
src = normalizePath('.'),
script = 'leaflet.polylineDecorator.js')
registerPlugin <- function(map, plugin) {
map$dependencies <- c(map$dependencies, list(plugin))
map
}
ui <- bootstrapPage(
tags$style(type = "text/css", "html, body {width:100%;height:100%}"),
leafletOutput("map", width = "100%", height = "100%")
)
server <- function(input, output) {
dat <- data.frame(lat0=c(29,29.1),lat1=c(30,30.1), lng0=c(-96,-96.1),lng1=c(-95,-95.1))
output$map <- renderLeaflet({
m <- leaflet() %>%
# addProviderTiles(providers$OpenStreetMap.BlackAndWhite) %>%
setView(lat=29.762778, lng=-95.383056, zoom=8) # Houston
})
observe({
# THIS DOESNT WORK with PROXY!!!
leafletProxy('map') %>%
registerPlugin(polylineDecoratorPlugin) %>%
addPolylines(lat=c(dat$lat0[1], dat$lat1[1]), lng=c(dat$lng0[1],dat$lng1[1])) %>%
addPolylines(lat=c(dat$lat0[2], dat$lat1[2]), lng=c(dat$lng0[2],dat$lng1[2])) %>%
htmlwidgets::onRender("function(el,x,data) {
for(var i=0; i < data.lat0.length; i++) {
var dec = L.polylineDecorator([[data.lat0[i],data.lng0[i]],[data.lat1[i],data.lng1[i]]], {
patterns: [
{offset: 0, repeat: 20, symbol: L.Symbol.arrowHead({pixelSize:15, pathOptions:{stroke:true}})}
]
}).addTo(this);
}
}",
data=dat)
})
}
# Run the application
shinyApp(ui = ui, server = server)
And here is the the results from example 2. As you see there is no decorator, only lines, though i attempted to use htmlwidgets::onRender pretty much the same way.

Answer 1

Alright, I may have nailed it down.
What I had to do are:
Call htmlwidgets::onRender with leaflet, not with leafletProxy. I have to anticipate what to come when I make map.
When I add polylines using lealetProxy, i dicipline myself to add extra option need_decorator=TRUE.
Call back function for htmlwidgets::onRender should add event listener to the map. in the code below it is this part: myMap.on('layeradd', function(e) {...} );. So the decorator is going to be added when layer is added.
We want to add decorator to polyline. So i need if ('need_decorator' in lyr.options) this testing if the layer which triggered event was polyline that i want to have decorator. Without this test, polyline decorator is going to trigger the event and goes infinite loop of calling itself.
Sample code below generates what I wanted. This may have been obvious to people with experience with javascript, but a lot of R user like me don't have much experience with this event kind of thing...
I want to deal with cases when polyline got modified/deleted, but I guess idea would be the same.
Please let me know if there is simpler way to do this.
library(shiny)
library(leaflet)
library(htmltools)
download.file(
'https://raw.githubusercontent.com/bbecquet/Leaflet.PolylineDecorator/master/dist/leaflet.polylineDecorator.js',
'leaflet.polylineDecorator.js')
polylineDecoratorPlugin <- htmlDependency('Leaflet.PolylineDecorator',
'1.6.0',
src = normalizePath('.'),
script = 'leaflet.polylineDecorator.js')
registerPlugin <- function(map, plugin) {
map$dependencies <- c(map$dependencies, list(plugin))
map
}
ui <- bootstrapPage(
tags$style(type = "text/css", "html, body {width:100%;height:100%}"),
leafletOutput("map", width = "100%", height = "100%")
)
server <- function(input, output) {
dat <- data.frame(lat0=c(29,29.1),lat1=c(30,30.1), lng0=c(-96,-96.1),lng1=c(-95,-95.1))
output$map <- renderLeaflet({
m <- leaflet() %>%
registerPlugin(polylineDecoratorPlugin) %>%
addProviderTiles(providers$CartoDB.Positron) %>%
setView(lat=29.762778, lng=-95.383056, zoom=8) %>% # Houston
htmlwidgets::onRender(
"function(el,x,data) {
var myMap = this;
// I have to wrap the decoration addition code with map.on() function
// wait for polyline layer to be added before i add decorator
myMap.on('layeradd',
function(e) {
var lyr = e.layer;
// among whatever layers added to the map, i look for
// 'need_decorator' property which i tell myself to add as an options
// when adding polyline
if ('need_decorator' in lyr.options) {
var dec = L.polylineDecorator(lyr, {
patterns: [
{offset: 0, repeat: 20, symbol: L.Symbol.arrowHead({pixelSize:15, pathOptions:{stroke:true}})}
]
}).addTo(myMap);
}
}
);
}",
data=dat)
})
observe({
leafletProxy('map') %>%
# I am adding need_decorator = TRUE as an option. This shows up as, when
# event got triggered, event.layer.options.need_decorator in Javascript
addPolylines(lat=c(dat$lat0[1], dat$lat1[1]), lng=c(dat$lng0[1],dat$lng1[1]), options = list(need_decorator = T)) %>%
addPolylines(lat=c(dat$lat0[2], dat$lat1[2]), lng=c(dat$lng0[2],dat$lng1[2]), options = list(need_decorator = T))
})
}
# Run the application
shinyApp(ui = ui, server = server)
EDIT
(2020-04-30)
openstreetmap provider tile doesnt exist anymore, so i change to cartodb. Confirmed that it is still working.