Very slow hover interactions in OpenLayers 3 with any browser except Chrome - openlayers-3

Question

I have two styles of interactions, one highlights the feature, the second places a tooltop with the feature name. Commenting both out, they're very fast, leave either in, the map application slows in IE and Firefox (but not Chrome).
map.addInteraction(new ol.interaction.Select({
condition: ol.events.condition.pointerMove,
layers: [stationLayer],
style: null // this is actually a style function but even as null it slows
}));
$(map.getViewport()).on('mousemove', function(evt) {
if(!dragging) {
var pixel = map.getEventPixel(evt.originalEvent);
var feature = null;
// this block directly below is the offending function, comment it out and it works fine
map.forEachFeatureAtPixel(pixel, function(f, l) {
if(f.get("type") === "station") {
feature = f;
}
});
// commenting out just below (getting the feature but doing nothing with it, still slow
if(feature) {
target.css("cursor", "pointer");
$("#FeatureTooltip").html(feature.get("name"))
.css({
top: pixel[1]-10,
left: pixel[0]+15
}).show();
} else {
target.css("cursor", "");
$("#FeatureTooltip").hide();
}
}
});
I mean this seems like an issue with OpenLayers-3 but I just wanted to be sure I wasn't overlooking something else here.
Oh yeah, there's roughly 600+ points. Which is a lot, but not unreasonably so I would think. Zooming-in to limit the features in view definitely helps. So I guess this is a # of features issue.

Answer 1

This is a known bug and needs more investigation. You can track progress here: https://github.com/openlayers/ol3/issues/4232.
However, there is one thing you can do to make things faster: return a truthy value from map.forEachFeatureAtPixel to stop checking for features once one was found:
var feature = map.forEachFeatureAtPixel(pixel, function(f) {
if (f.get('type') == 'station') {
return feature;
}
});

Answer 2

i had same issue, solved a problem by setInterval, about this later
1) every mouse move to 1 pixel fires event, and you will have a quee of event till you stop moving, and the quee will run in calback function, and freezes
2) if you have an objects with difficult styles, all element shown in canvas will take time to calculate for if they hit the cursor
resolve:
1. use setInterval
2. check for pixels moved size from preview, if less than N, return
3. for layers where multiple styles, try to simplify them by dividing into multiple ones, and let only one layer by interactive for cursor move
function mouseMove(evt) {
clearTimeout(mm.sheduled);
function squareDist(coord1, coord2) {
var dx = coord1[0] - coord2[0];
var dy = coord1[1] - coord2[1];
return dx * dx + dy * dy;
}
if (mm.isActive === false) {
map.unByKey(mm.listener);
return;
}
//shedules FIFO, last pixel processed after 200msec last process
const elapsed = (performance.now() - mm.finishTime);
const pixel = evt.pixel;
const distance = squareDist(mm.lastP, pixel);
if (distance > 0) {
mm.lastP = pixel;
mm.finishTime = performance.now();
mm.sheduled = setTimeout(function () {
mouseMove(evt);
}, MIN_ELAPSE_MSEC);
return;
} else if (elapsed < MIN_ELAPSE_MSEC || mm.working === true) {
// console.log(`distance = ${distance} and elapsed = ${elapsed} mesc , it never should happen`);
mm.sheduled = setTimeout(function () {
mouseMove(evt);
}, MIN_ELAPSE_MSEC);
return;
}
//while multithreading is not working on browsers, this flag is unusable
mm.working = true;
let t = performance.now();
//region drag map
const vStyle = map.getViewport().style;
vStyle.cursor = 'default';
if (evt.dragging) {
vStyle.cursor = 'grabbing';
}//endregion
else {
//todo replace calback with cursor=wait,cursor=busy
UtGeo.doInCallback(function () {
checkPixel(pixel);
});
}
mm.finishTime = performance.now();
mm.working = false;
console.log('mm finished', performance.now() - t);
}

Answer 3

In addition to #ahocevar's answer, a possible optimization for you is to utilize the select interaction's select event.
It appears that both the select interaction and your mousemove listener are both checking for hits on the same layers, doing double work. The select interaction will trigger select events whenever the set of selected features changes. You could listen to it, and show the popup whenever some feature is selected and hide it when not.
This should reduce the work by half, assuming that forEachFeatureAtPixel is what's hogging the system.