fix: add map camera state tracking (#84)

Camera state tracking allows the Map component to avoid a feedback-loop when camera values published by the map are fed back into the Map component props.

I measured round-trip times (dispatching an event into the react-application and receiving them back as props) of around 4-5ms. However, there are cases where this roundtrip crosses the frame-boundary, and times more like 20ms can be observed. When this happens, stuttering, janky animations and suboptimal interactions will happen.

src/components/__tests__/map.test.tsx

@@ -150,3 +150,16 @@ describe('creating and updating map instance', () => {
     expect(options).toMatchObject({mapId: 'othermapid'});
   });
 });
+
+describe('map events and event-props', () => {
+  test.todo('events dispatched by the map are received via event-props');
+});
+
+describe('camera updates', () => {
+  test.todo('initial camera state is passed via mapOptions, not moveCamera');
+  test.todo('updated camera state is passed to moveCamera');
+  test.todo("re-renders with unchanged camera state don't trigger moveCamera");
+  test.todo(
+    "re-renders with props received via events don't trigger moveCamera"
+  );
+});

src/components/map/index.tsx

@@ -17,6 +17,7 @@ import {useCallbackRef} from '../../libraries/use-callback-ref';
 import {MapEventProps, useMapEvents} from './use-map-events';
 import {useMapOptions} from './use-map-options';
 import {useDeckGLCameraUpdate} from './use-deckgl-camera-update';
+import {useInternalCameraState} from './use-internal-camera-state';
 
 export interface GoogleMapsContextValue {
   map: google.maps.Map | null;
@@ -73,8 +74,9 @@ export const Map = (props: PropsWithChildren<MapProps>) => {
   }
 
   const [map, mapRef] = useMapInstance(props, context);
-  useMapOptions(map, props);
-  useMapEvents(map, props);
+  const cameraStateRef = useInternalCameraState();
+  useMapOptions(map, cameraStateRef, props);
+  useMapEvents(map, cameraStateRef, props);
   useDeckGLCameraUpdate(map, viewState);
 
   const isViewportSet = useMemo(() => Boolean(viewport), [viewport]);

src/components/map/use-internal-camera-state.ts

@@ -0,0 +1,47 @@
+import {MutableRefObject, useRef} from 'react';
+import {MapCameraChangedEvent, MapEvent} from './use-map-events';
+
+export type InternalCameraState = {
+  center: google.maps.LatLngLiteral;
+  heading: number;
+  tilt: number;
+  zoom: number;
+};
+
+export type InternalCameraStateRef = MutableRefObject<InternalCameraState>;
+
+/**
+ * Creates a mutable ref object to track the last known state of the map camera.
+ * This is updated by `trackDispatchedEvent` and used in `useMapOptions`.
+ */
+export function useInternalCameraState(): InternalCameraStateRef {
+  return useRef<InternalCameraState>({
+    center: {lat: 0, lng: 0},
+    heading: 0,
+    tilt: 0,
+    zoom: 0
+  });
+}
+
+/**
+ * Records camera data from the last event dispatched to the React application
+ * in a mutable `IternalCameraStateRef`.
+ * This data can then be used to prevent feeding these values back to the
+ * map-instance when a typical "controlled component" setup (state variable is
+ * fed into and updated by the map).
+ */
+export function trackDispatchedEvent(
+  ev: MapEvent,
+  cameraStateRef: InternalCameraStateRef
+) {
+  const cameraEvent = ev as MapCameraChangedEvent;
+
+  // we're only interested in the camera-events here
+  if (!cameraEvent.detail.center) return;
+  const {center, zoom, heading, tilt} = cameraEvent.detail;
+
+  cameraStateRef.current.center = center;
+  cameraStateRef.current.heading = heading;
+  cameraStateRef.current.tilt = tilt;
+  cameraStateRef.current.zoom = zoom;
+}

src/components/map/use-map-events.ts

@@ -1,4 +1,8 @@
 import {useEffect} from 'react';
+import {
+  InternalCameraStateRef,
+  trackDispatchedEvent
+} from './use-internal-camera-state';
 
 /**
  * Handlers for all events that could be emitted by map-instances.
@@ -40,6 +44,7 @@ export type MapEventProps = Partial<{
  */
 export function useMapEvents(
   map: google.maps.Map | null,
+  cameraStateRef: InternalCameraStateRef,
   props: MapEventProps
 ) {
   // note: calling a useEffect hook from within a loop is prohibited by the
@@ -61,12 +66,15 @@ export function useMapEvents(
       const listener = map.addListener(
         eventType,
         (ev?: google.maps.MapMouseEvent | google.maps.IconMouseEvent) => {
-          handler(createMapEvent(eventType, map, ev));
+          const mapEvent = createMapEvent(eventType, map, ev);
+
+          trackDispatchedEvent(mapEvent, cameraStateRef);
+          handler(mapEvent);
         }
       );
 
       return () => listener.remove();
-    }, [map, eventType, handler]);
+    }, [map, cameraStateRef, eventType, handler]);
   }
 }
 
@@ -189,7 +197,7 @@ const mouseEventTypes = [
 type MapEventPropName = keyof MapEventProps;
 const eventPropNames = Object.keys(propNameToEventType) as MapEventPropName[];
 
-type MapEvent<T = unknown> = {
+export type MapEvent<T = unknown> = {
   type: string;
   map: google.maps.Map;
   detail: T;

src/components/map/use-map-options.ts

@@ -1,13 +1,32 @@
 import {useEffect, useLayoutEffect} from 'react';
 import {MapProps} from '@vis.gl/react-google-maps';
+import {InternalCameraStateRef} from './use-internal-camera-state';
+import {isLatLngLiteral} from '../../libraries/is-lat-lng-literal';
 
 /**
- * Internal hook to update the map-options and view-parameters when
+ * Internal hook to update the map-options and camera parameters when
  * props are changed.
+ *
+ * @param map the map instance
+ * @param cameraStateRef stores the last values seen during dispatch into the
+ * react-application in useMapEvents(). We can safely assume that we
+ * don't need to feed these values back into the map.
+ * @param mapProps the props to update the map-instance with
  * @internal
  */
-export function useMapOptions(map: google.maps.Map | null, mapProps: MapProps) {
-  const {center, zoom, heading, tilt, ...mapOptions} = mapProps;
+export function useMapOptions(
+  map: google.maps.Map | null,
+  cameraStateRef: InternalCameraStateRef,
+  mapProps: MapProps
+) {
+  const {center: rawCenter, zoom, heading, tilt, ...mapOptions} = mapProps;
+  const center = rawCenter
+    ? isLatLngLiteral(rawCenter)
+      ? rawCenter
+      : rawCenter.toJSON()
+    : null;
+  const lat = center && center.lat;
+  const lng = center && center.lng;
 
   /* eslint-disable react-hooks/exhaustive-deps --
    *
@@ -17,32 +36,48 @@ export function useMapOptions(map: google.maps.Map | null, mapProps: MapProps) {
    */
 
   // update the map options when mapOptions is changed
+  // Note: due to the destructuring above, mapOptions will be seen as changed
+  //   with every re-render, so we're boldly assuming the maps-api will properly
+  //   deal with unchanged option-values passed into setOptions.
   useEffect(() => {
     if (!map) return;
 
-    map.setOptions(mapOptions);
+    // Changing the mapId via setOptions will trigger an error-message.
+    // We will re-create the map-instance in that case anyway, so we
+    // remove it here to avoid this error-message.
+    // eslint-disable-next-line @typescript-eslint/no-unused-vars
+    const {mapId, ...opts} = mapOptions;
+    map.setOptions(opts);
   }, [mapOptions]);
 
   useLayoutEffect(() => {
-    if (!map || !center) return;
+    if (!map || !Number.isFinite(lat) || !Number.isFinite(lng)) return;
+    if (
+      cameraStateRef.current.center.lat === lat &&
+      cameraStateRef.current.center.lng === lng
+    )
+      return;
 
-    map.moveCamera({center});
-  }, [center]);
+    map.moveCamera({center: {lat: lat as number, lng: lng as number}});
+  }, [lat, lng]);
 
   useLayoutEffect(() => {
     if (!map || !Number.isFinite(zoom)) return;
+    if (cameraStateRef.current.zoom === zoom) return;
 
     map.moveCamera({zoom: zoom as number});
   }, [zoom]);
 
   useLayoutEffect(() => {
     if (!map || !Number.isFinite(heading)) return;
+    if (cameraStateRef.current.heading === heading) return;
 
     map.moveCamera({heading: heading as number});
   }, [heading]);
 
   useLayoutEffect(() => {
     if (!map || !Number.isFinite(tilt)) return;
+    if (cameraStateRef.current.tilt === tilt) return;
 
     map.moveCamera({tilt: tilt as number});
   }, [tilt]);

src/libraries/is-lat-lng-literal.ts

@@ -0,0 +1,8 @@
+export function isLatLngLiteral(
+  obj: unknown
+): obj is google.maps.LatLngLiteral {
+  if (!obj || typeof obj !== 'object') return false;
+  if (!('lat' in obj && 'lng' in obj)) return false;
+
+  return Number.isFinite(obj.lat) && Number.isFinite(obj.lng);
+}