test: fix scroll flicker 2

web/src/lib/managers/timeline-manager/internal/intersection-support.svelte.ts

@@ -67,3 +67,11 @@ export function calculateViewerAssetViewportProximity(
     timelineManager.visibleWindow.bottom + headerHeight,
   );
 }
+
+export function calculateViewerAssetIsInOrNearViewport(
+  timelineManager: TimelineManager,
+  positionTop: number,
+  positionHeight: number,
+) {
+  return isInOrNearViewport(calculateViewerAssetViewportProximity(timelineManager, positionTop, positionHeight));
+}

web/src/lib/managers/timeline-manager/timeline-month.svelte.ts

@@ -29,7 +29,8 @@ import type { AssetDescriptor, Direction, MoveAsset, TimelineAsset } from './typ
 import { ViewerAsset } from './viewer-asset.svelte';
 
 export class TimelineMonth {
-  #viewportProximity: ViewportProximity = $state(ViewportProximity.FarFromViewport);
+  #isInOrNearViewport = $state(false);
+  #isInViewport = $state(false);
   isLoaded: boolean = $state(false);
   timelineDays: TimelineDay[] = $state([]);
   readonly timelineManager: TimelineManager;
@@ -85,24 +86,28 @@ export class TimelineMonth {
   }
 
   set viewportProximity(newValue: ViewportProximity) {
-    const old = this.#viewportProximity;
-    if (old === newValue) {
-      return;
+    const isInOrNearViewport = isInOrNearViewportUtil(newValue);
+    if (this.#isInOrNearViewport !== isInOrNearViewport) {
+      this.#isInOrNearViewport = isInOrNearViewport;
+      if (isInOrNearViewport) {
+        void this.timelineManager.loadTimelineMonth(this.yearMonth);
+      } else {
+        this.cancel();
+      }
     }
-    this.#viewportProximity = newValue;
-    if (isInOrNearViewportUtil(newValue)) {
-      void this.timelineManager.loadTimelineMonth(this.yearMonth);
-    } else {
-      this.cancel();
+
+    const isInViewport = isInViewportUtil(newValue);
+    if (this.#isInViewport !== isInViewport) {
+      this.#isInViewport = isInViewport;
     }
   }
 
   get isInOrNearViewport() {
-    return isInOrNearViewportUtil(this.#viewportProximity);
+    return this.#isInOrNearViewport;
   }
 
   get isInViewport() {
-    return isInViewportUtil(this.#viewportProximity);
+    return this.#isInViewport;
   }
 
   get lastTimelineDay() {

web/src/lib/managers/timeline-manager/viewer-asset.svelte.ts

@@ -1,28 +1,24 @@
 import type { CommonPosition } from '$lib/utils/layout-utils';
-import {
-  ViewportProximity,
-  calculateViewerAssetViewportProximity,
-  isInOrNearViewport,
-} from './internal/intersection-support.svelte';
+import { calculateViewerAssetIsInOrNearViewport } from './internal/intersection-support.svelte';
 import type { TimelineDay } from './timeline-day.svelte';
 import type { TimelineAsset } from './types';
 
 export class ViewerAsset {
   readonly #group: TimelineDay;
 
-  #viewportProximity = $derived.by(() => {
+  #isInOrNearViewport = $derived.by(() => {
     if (!this.position) {
-      return ViewportProximity.FarFromViewport;
+      return false;
     }
 
     const store = this.#group.timelineMonth.timelineManager;
     const positionTop = this.#group.absoluteTimelineDayTop + this.position.top;
 
-    return calculateViewerAssetViewportProximity(store, positionTop, this.position.height);
+    return calculateViewerAssetIsInOrNearViewport(store, positionTop, this.position.height);
   });
 
   get isInOrNearViewport() {
-    return isInOrNearViewport(this.#viewportProximity);
+    return this.#isInOrNearViewport;
   }
 
   position: CommonPosition | undefined = $state.raw();