feat(core): smooth noisy pinch frames before applying zoom

modules/core/src/controllers/controller.ts

@@ -20,6 +20,10 @@ const NO_TRANSITION_PROPS = {
 
 const DEFAULT_INERTIA = 300;
 const INERTIA_EASING = t => 1 - (1 - t) * (1 - t);
+// Cap how much the smoothed log-scale can change per pinch event. 0.18 log2
+// units ≈ a 1.13× zoom per frame, well above any realistic pinch rate but
+// low enough to swallow the spike from a single noisy final-lift frame.
+const MAX_PINCH_ZOOM_DELTA_PER_EVENT = 0.18;
 
 const EVENT_TYPES = {
   WHEEL: ['wheel'],
@@ -112,6 +116,10 @@ export type ViewStateChangeParameters<ViewStateT = any> = {
 
 const pinchEventWorkaround: any = {};
 
+function clampPinchZoomDelta(delta: number): number {
+  return Math.max(-MAX_PINCH_ZOOM_DELTA_PER_EVENT, Math.min(MAX_PINCH_ZOOM_DELTA_PER_EVENT, delta));
+}
+
 export default abstract class Controller<ControllerState extends IViewState<ControllerState>> {
   abstract get ControllerState(): ConstructorOf<ControllerState>;
   abstract get transition(): TransitionProps;
@@ -650,6 +658,7 @@ export default abstract class Controller<ControllerState extends IViewState<Cont
     // hack - hammer's `rotation` field doesn't seem to produce the correct angle
     pinchEventWorkaround._startPinchRotation = event.rotation;
     pinchEventWorkaround._lastPinchEvent = event;
+    pinchEventWorkaround._smoothedPinchScaleLog = 0;
     this.updateViewport(newControllerState, NO_TRANSITION_PROPS, {isDragging: true});
     return true;
   }
@@ -667,7 +676,14 @@ export default abstract class Controller<ControllerState extends IViewState<Cont
     if (this.touchZoom) {
       const {scale} = event;
       const pos = this.getCenter(event);
-      newControllerState = newControllerState.zoom({pos, scale});
+      // Apply the raw pinch scale in log space, clamped per event so a single
+      // noisy frame (especially on touch lift) can't introduce a jump.
+      const rawScaleLog = Math.log2(scale);
+      const previousScaleLog = pinchEventWorkaround._smoothedPinchScaleLog ?? 0;
+      const smoothedScaleLog =
+        previousScaleLog + clampPinchZoomDelta(rawScaleLog - previousScaleLog);
+      pinchEventWorkaround._smoothedPinchScaleLog = smoothedScaleLog;
+      newControllerState = newControllerState.zoom({pos, scale: Math.pow(2, smoothedScaleLog)});
     }
     if (this.touchRotate) {
       const {rotation} = event;
@@ -727,6 +743,7 @@ export default abstract class Controller<ControllerState extends IViewState<Cont
     }
     pinchEventWorkaround._startPinchRotation = null;
     pinchEventWorkaround._lastPinchEvent = null;
+    pinchEventWorkaround._smoothedPinchScaleLog = null;
     return true;
   }
 

test/modules/core/controllers/controllers.spec.ts

@@ -35,6 +35,45 @@ test('MapController#inertia', async () => {
   });
 });
 
+test('MapController clamps a noisy final pinch frame instead of jumping', () => {
+  // Simulate a normal pinch ending with one sensor-noise spike. Without the
+  // per-event log-scale clamp the spike would propagate straight into the zoom.
+  const makePinchEvent = (type: string, scale: number, deltaTime: number) => ({
+    type,
+    offsetCenter: {x: 50, y: 50},
+    scale,
+    rotation: 0,
+    deltaTime,
+    srcEvent: {preventDefault() {}},
+    stopPropagation() {}
+  });
+
+  const controller = createTestController({
+    view: new MapView({controller: true}),
+    initialViewState: {
+      longitude: -122.45,
+      latitude: 37.78,
+      zoom: 10,
+      pitch: 30,
+      bearing: -45
+    }
+  });
+
+  controller.handleEvent(makePinchEvent('pinchstart', 1, 0) as any);
+  controller.handleEvent(makePinchEvent('pinchmove', 1.05, 16) as any);
+  controller.handleEvent(makePinchEvent('pinchmove', 1.1, 32) as any);
+  const zoomBeforeSpike = controller.props.zoom as number;
+  // 100x scale on a single frame is the kind of spike a noisy lift produces.
+  controller.handleEvent(makePinchEvent('pinchmove', 100, 48) as any);
+
+  const delta = (controller.props.zoom as number) - zoomBeforeSpike;
+  // The per-event log2 delta cap is 0.18.
+  expect(
+    delta,
+    'noisy final pinch frame is clamped to the per-event log-scale cap'
+  ).toBeLessThanOrEqual(0.18 + 1e-6);
+});
+
 test('GlobeController', async () => {
   await testController(
     GlobeView,