Leaflet custom icon resize on zoom. Performance icon vs divicon

Question

I was trying to resize my custom icons when zooming in leaflet. I came up with two solutions for this. One using the L.Icon tag, the other one using L.divIcon. In both examples I only set 1 marker and group for readability

Method 1 using L.Icon: make groups with markers. Then on zoomend i use mygroup.eachLayer(function (layer) to change all icons for 1 layer using layer.setIcon(). I repeat this for all groups

<script>
// Setting map options
....

// Setting Icon
var normalicon = L.icon({
    iconUrl: 'icon1.jpg',
    iconSize:     [40,40],
    iconAnchor:   [20,20],
    popupAnchor:  [0,-20] 
    });


// Create a group
var normalLayer = L.layerGroup([
    L.marker([200,200], {icon:normalicon})
]).addTo(map);

// Resizing on zoom
map.on('zoomend', function() {

    // Normal icons
    var normaliconresized = L.Icon.extend({
        options: {
            iconSize: [20*(map.getZoom()+2), 20*(map.getZoom()+2)], // New size!
            iconAnchor:   [20,20],
            popupAnchor:  [0,-20]
        }
    });

    var normaliconchange = new normaliconresized({iconUrl: 'icon1.jpg'})
    normalLayer.eachLayer(function (layer) {
        layer.setIcon(normaliconchange);
    });

    .... Do the same for the other groups
});             
</script>

Method 2 using L.divIcon: I make the icons and the different groups and add some CSS for each icon with a background-image property. Then on zoomend I simply use JQuery to change the css. background-size css-property allows me to change the image size. I do this for each divIcon class I have

Css
.iconsdiv{
    width:20px; height:20px;
    background-image:url("icon2.jpg");
    background-size: 20px 20px;
}


Script
<script>
// Setting map options
....


// Setting Icon

var divicon = L.divIcon({className: 'iconsdiv', iconSize: null }); // Explicitly set to null or you will default to 12x12


// Create a group
var divLayer = L.layerGroup([
    L.marker([200,200], {icon:divicon})
]).addTo(map);


// Resizing on zoom
map.on('zoomend', function() {

    var newzoom = '' + (20*(map.getZoom()+2)) +'px';
    $('#map .iconsdiv').css({'width':newzoom,'height':newzoom,'background-size':newzoom + ' ' + newzoom}); 

     ... repeat for the other classes
});


</script>

I have barely any experience with javascript/jquery/...

Is the second option preferable as it does not require re-setting each icon? Would it improve performance when there is a large number of groups/icons?

Answer 1

I did a test myself using performance.now(). I tested on a 1024x1180 (bounds) custom map. Once with 676 makers. Then with about half of this and lastly with 100 markers. The performance was measured inside the map.on('zoomend', function() { function.

• For 676 markers it took 2500-2900 milliseconds for the L.Iconmethod to update. For the L.divIconthis was only 10-30 milliseconds.
• Half the amount of markers also halved this time.
• For about 100 markers (104) L.Icon took 300-400 milliseconds to update. L.divIcon did the same in only 4-5 milliseconds.

I also timed the performance of the initialization (L.layerGroup([...]).addTo(map)) for 676 markers. L.Icon took 2200-2400 milliseconds. L.divIcon did the same in 80-95 milliseconds.

L.divIcon clearly does a lot better (as expected). While it is a bit of a cheat, I guess I would prefer using this method. I can not directly think of reasons why the L.Iconmethod would be preferred in case we want zooming

Edit: I noticed that according to Leaflet Documentation 'Icon' you can also assign a className to the Icons. Using css-properties width and height the same can be done as I did earlier for the divIcons, thus saving you a lot of loading time, yet allowing you to use all options linked to L.Icon. Your initialisation time will still be longer though.