debounce rounding position on Marker

src/ui/marker.js

@@ -81,6 +81,8 @@ export default class Marker extends Evented {
     _rotationAlignment: string;
     _originalTabIndex: ?string; // original tabindex of _element
     _fadeTimer: ?TimeoutID;
+    _updateFrameId: number;
+    _updateMoving: () => void;
 
     constructor(options?: Options, legacyOptions?: Options) {
         super();
@@ -110,6 +112,7 @@ export default class Marker extends Evented {
         this._rotation = options && options.rotation || 0;
         this._rotationAlignment = options && options.rotationAlignment || 'auto';
         this._pitchAlignment = options && options.pitchAlignment && options.pitchAlignment !== 'auto' ?  options.pitchAlignment : this._rotationAlignment;
+        this._updateMoving = () => this._update(true);
 
         if (!options || !options.element) {
             this._defaultMarker = true;
@@ -184,10 +187,13 @@ export default class Marker extends Evented {
      *     .addTo(map); // add the marker to the map
      */
     addTo(map: Map) {
+        if (map === this._map) {
+            return this;
+        }
         this.remove();
         this._map = map;
         map.getCanvasContainer().appendChild(this._element);
-        map.on('move', this._update);
+        map.on('move', this._updateMoving);
         map.on('moveend', this._update);
         map.on('remove', this._clearFadeTimer);
         map._addMarker(this);
@@ -213,7 +219,7 @@ export default class Marker extends Evented {
     remove() {
         if (this._map) {
             this._map.off('click', this._onMapClick);
-            this._map.off('move', this._update);
+            this._map.off('move', this._updateMoving);
             this._map.off('moveend', this._update);
             this._map.off('mousedown', this._addDragHandler);
             this._map.off('touchstart', this._addDragHandler);
@@ -268,7 +274,7 @@ export default class Marker extends Evented {
         this._lngLat = LngLat.convert(lnglat);
         this._pos = null;
         if (this._popup) this._popup.setLngLat(this._lngLat);
-        this._update();
+        this._update(true);
         return this;
     }
 
@@ -446,41 +452,60 @@ export default class Marker extends Evented {
             position.y >= 0 && position.y < tr.height;
     }
 
-    _update(e?: {type: 'move' | 'moveend'}) {
-        if (!this._map) return;
+    _updateDOM() {
+        const pos = this._pos || new Point(0, 0);
+        const pitch = this._calculatePitch();
+        const rotation  = this._calculateRotation();
+        this._element.style.transform = `${anchorTranslate[this._anchor]} translate(${pos.x}px, ${pos.y}px) rotateX(${pitch}deg) rotateZ(${rotation}deg)`;
+    }
 
-        if (this._map.transform.renderWorldCopies) {
-            this._lngLat = smartWrap(this._lngLat, this._pos, this._map.transform);
+    _calculatePitch() {
+        if (this._pitchAlignment === "viewport" || this._pitchAlignment === "auto") {
+            return 0;
+        } if (this._pitchAlignment === "map") {
+            return this._map.getPitch();
         }
+        return 0;
+    }
 
-        this._pos = this._map.project(this._lngLat)._add(this._transformedOffset());
-
-        let rotation = "";
+    _calculateRotation() {
         if (this._rotationAlignment === "viewport" || this._rotationAlignment === "auto") {
-            rotation = `rotateZ(${this._rotation}deg)`;
-        } else if (this._rotationAlignment === "map") {
-            rotation = `rotateZ(${this._rotation - this._map.getBearing()}deg)`;
+            return this._rotation;
+        } if (this._rotationAlignment === "map") {
+            return this._rotation - this._map.getBearing();
         }
+        return 0;
+    }
 
-        let pitch = "";
-        if (this._pitchAlignment === "viewport" || this._pitchAlignment === "auto") {
-            pitch = "rotateX(0deg)";
-        } else if (this._pitchAlignment === "map") {
-            pitch = `rotateX(${this._map.getPitch()}deg)`;
+    _update(delaySnap?: boolean) {
+        window.cancelAnimationFrame(this._updateFrameId);
+        if (!this._map) return;
+
+        if (this._map.transform.renderWorldCopies) {
+            this._lngLat = smartWrap(this._lngLat, this._pos, this._map.transform);
         }
 
+        this._pos = this._map.project(this._lngLat)._add(this._transformedOffset());
+
         // because rounding the coordinates at every `move` event causes stuttered zooming
         // we only round them when _update is called with `moveend` or when its called with
         // no arguments (when the Marker is initialized or Marker#setLngLat is invoked).
-        if (!e || e.type === "moveend") {
+        if (delaySnap === true) {
+            this._updateFrameId = window.requestAnimationFrame(() => {
+                if (this._element && this._pos && this._anchor) {
+                    this._pos = this._pos.round();
+                    this._updateDOM();
+                }
+            });
+        } else {
             this._pos = this._pos.round();
         }
 
         this._map._requestDomTask(() => {
             if (!this._map) return;
 
             if (this._element && this._pos && this._anchor) {
-                this._element.style.transform = `${anchorTranslate[this._anchor]} translate(${this._pos.x}px, ${this._pos.y}px) ${pitch} ${rotation}`;
+                this._updateDOM();
             }
 
             if ((this._map.getTerrain() || this._map.getFog()) && !this._fadeTimer) {

test/unit/ui/marker.test.js

@@ -4,6 +4,7 @@ import {createMap as globalCreateMap} from '../../util/index.js';
 import Marker from '../../../src/ui/marker.js';
 import Popup from '../../../src/ui/popup.js';
 import LngLat from '../../../src/geo/lng_lat.js';
+import {Event} from '../../../src/util/evented.js';
 import Point from '@mapbox/point-geometry';
 import simulate from '../../util/simulate_interaction.js';
 
@@ -921,3 +922,47 @@ test('Marker and fog', (t) => {
         });
     });
 });
+
+test('Snap To Pixel', (t) => {
+    const map = createMap(t);
+    const marker = new Marker({draggable: true})
+        .setLngLat([1, 2])
+        .addTo(map);
+    t.test("Snap To Pixel immediately after initializing marker", (t) => {
+        t.same(marker._pos, marker._pos.round());
+        t.end();
+    });
+    t.test("Not Immediately Snap To Pixel After setLngLat", (t) => {
+        marker.setLngLat([2, 1]);
+        const pos = marker._pos;
+        setTimeout(() => {
+            t.notSame(marker._pos, pos);
+            t.same(marker._pos, pos.round());
+            t.end();
+        }, 100);
+    });
+    t.test("Immediately Snap To Pixel on moveend", (t) => {
+        map.fire(new Event("moveend"));
+        t.same(marker._pos, marker._pos.round());
+        t.end();
+    });
+    t.test("Not Immediately Snap To Pixel when Map move", (t) => {
+        map.fire(new Event("move"));
+        t.notSame(marker._pos, marker._pos.round());
+        window.requestAnimationFrame(() => {
+            t.same(marker._pos, marker._pos.round());
+            t.end();
+        });
+    });
+    t.test("Not Immediately Snap To Pixel when Map move and setLngLat", (t) => {
+        marker.setLngLat([1, 2]);
+        map.fire(new Event("move"));
+        t.notSame(marker._pos, marker._pos.round());
+        setTimeout(() => {
+            t.same(marker._pos, marker._pos.round());
+            t.end();
+        }, 100);
+    });
+    map.remove();
+    t.end();
+});