perf(queue): virtualize the queue list (#857)

* perf(queue): virtualize the queue list

Render the QueuePanel queue through @tanstack/react-virtual so the DOM stays
O(visible rows) instead of O(queue length) — a 10k+ Artist Radio queue no
longer creates tens of thousands of DOM nodes. Row logic (reorder DnD, radio/
auto dividers, lucky-mix loader, context menu) is unchanged, just wrapped in
the virtual rows. Auto-scroll to the next track moves out of useQueueAutoScroll
(which relied on every row being in the DOM) to a virtualizer scroll plus an
exact scrollIntoView on the real target row.

Phase 0 of the queue thin-state plan; no store/persist changes.

* docs(changelog): virtualized queue list (#857)

CHANGELOG.md

@@ -125,6 +125,14 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 
 
+### Queue — smoother scrolling for very long queues
+
+**By [@Psychotoxical](https://github.com/Psychotoxical), PR [#857](https://github.com/Psychotoxical/psysonic/pull/857)**
+
+* The queue panel now renders only the rows in view, so very long queues (e.g. hours of Artist Radio) stay smooth instead of bogging down the interface.
+
+
+
 ## Fixed
 
 ### In-page browse — virtual scroll and cover-art priority

src/components/QueuePanel.test.tsx

@@ -62,6 +62,20 @@ beforeEach(() => {
 });
 
 describe('QueuePanel — render surface', () => {
+  // jsdom has no layout, so the virtualized QueueList sees a 0px viewport and
+  // renders nothing. @tanstack/virtual-core measures via offsetHeight, so give
+  // the scroll viewport a height and rows a fixed height — then the virtualizer
+  // produces rows the way it does in the browser.
+  let offsetSpy: ReturnType<typeof vi.spyOn>;
+  beforeEach(() => {
+    offsetSpy = vi
+      .spyOn(HTMLElement.prototype, 'offsetHeight', 'get')
+      .mockImplementation(function (this: HTMLElement) {
+        return this.classList.contains('queue-list') ? 600 : 52;
+      });
+  });
+  afterEach(() => offsetSpy.mockRestore());
+
   it('renders an empty-queue affordance when the queue is empty', () => {
     const { container } = renderWithProviders(<QueuePanel />);
     expect(container.querySelector('.queue-panel')).not.toBeNull();

src/components/QueuePanel.tsx

@@ -160,7 +160,6 @@ function QueuePanelHostOrSolo() {
     queue,
     queueIndex,
     currentTrack,
-    activeTab,
     queueListRef,
     suppressNextAutoScrollRef,
   });

src/components/queuePanel/QueueList.tsx

@@ -1,4 +1,5 @@
-import React from 'react';
+import React, { useEffect } from 'react';
+import { useVirtualizer } from '@tanstack/react-virtual';
 import { Play } from 'lucide-react';
 import type { TFunction } from 'i18next';
 import OverlayScrollArea from '../OverlayScrollArea';
@@ -35,12 +36,52 @@ export function QueueList({
   suppressNextAutoScrollRef, isQueueDrag, psyDragFromIdxRef, externalDropTarget,
   startDrag, orbitAttributionLabel, luckyRolling, t,
 }: Props) {
+  // Virtualize so a 10k+ Artist-Radio queue keeps DOM at O(visible rows).
+  // Scroll element is the OverlayScrollArea viewport (`queueListRef`); rows have
+  // variable height (radio/auto dividers, lucky-mix loader) so we measure them.
+  const rowVirtualizer = useVirtualizer({
+    count: queue.length,
+    getScrollElement: () => queueListRef.current,
+    estimateSize: () => 52,
+    overscan: 10,
+    getItemKey: i => `${queue[i].id}:${i}`,
+    // Start with a sensible viewport height so rows render before the
+    // ResizeObserver reports the real size (SSR / jsdom, where the observer
+    // never fires). The real height overrides this on first measure.
+    initialRect: { width: 0, height: 600 },
+  });
+  const virtualItems = rowVirtualizer.getVirtualItems();
+  const totalSize = rowVirtualizer.getTotalSize();
+
+  // Auto-scroll the upcoming track into view on track change. Replaces the
+  // scrollIntoView path in useQueueAutoScroll, which relied on every row being
+  // in the DOM. Honours the suppression flag (row click / undo restore).
+  useEffect(() => {
+    if (suppressNextAutoScrollRef.current) {
+      suppressNextAutoScrollRef.current = false;
+      return;
+    }
+    if (activeTab !== 'queue' || queueIndex < 0 || queue.length === 0) return;
+    const target = Math.min(queueIndex + 1, queue.length - 1);
+    // First bring the target row into the rendered range via the virtualizer
+    // (estimate-based, so it can land a few px off). Then snap to the real DOM
+    // element so it sits flush at the top — no sliver of the now-playing row,
+    // which already shows in the header. scrollIntoView is exact (no estimate).
+    rowVirtualizer.scrollToIndex(target, { align: 'start' });
+    const id = requestAnimationFrame(() => {
+      const el = queueListRef.current?.querySelector<HTMLElement>(`[data-queue-idx="${target}"]`);
+      el?.scrollIntoView({ block: 'start', behavior: 'instant' });
+    });
+    return () => cancelAnimationFrame(id);
+  // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [queueIndex, activeTab]);
+
   return (
     <OverlayScrollArea
       viewportRef={queueListRef}
       className="queue-list-wrap"
       viewportClassName="queue-list"
-      measureDeps={[activeTab, queue.length]}
+      measureDeps={[activeTab, queue.length, totalSize]}
       railInset="panel"
       viewportScrollBehaviorAuto={isQueueDrag}
     >
@@ -49,8 +90,10 @@ export function QueueList({
           {t('queue.emptyQueue')}
         </div>
       ) : (
-        <>
-        {queue.map((track, idx) => {
+        <div style={{ height: totalSize, width: '100%', position: 'relative' }}>
+        {virtualItems.map(vi => {
+          const idx = vi.index;
+          const track = queue[idx];
           const isPlaying = idx === queueIndex;
           const isFirstAutoAdded = track.autoAdded && (idx === 0 || !queue[idx - 1].autoAdded);
           const isFirstRadioAdded = track.radioAdded && (idx === 0 || !queue[idx - 1].radioAdded);
@@ -67,7 +110,12 @@ export function QueueList({
           }
 
           return (
-            <React.Fragment key={`${track.id}-${idx}`}>
+            <div
+              key={vi.key}
+              data-index={idx}
+              ref={rowVirtualizer.measureElement}
+              style={{ position: 'absolute', top: 0, left: 0, width: '100%', transform: `translateY(${vi.start}px)` }}
+            >
             {isFirstRadioAdded && (
               <div className="queue-divider" style={{ margin: '2px 0' }}>
                 <span style={{ fontSize: '11px', fontWeight: 500, color: 'var(--text-muted)' }}>{t('queue.radioAdded')}</span>
@@ -154,10 +202,10 @@ export function QueueList({
                 </div>
               </button>
             )}
-            </React.Fragment>
+            </div>
           );
         })}
-        </>
+        </div>
       )}
     </OverlayScrollArea>
   );

src/hooks/useQueueAutoScroll.ts

@@ -1,4 +1,4 @@
-import React, { useEffect, useLayoutEffect } from 'react';
+import React, { useLayoutEffect } from 'react';
 import { registerQueueListScrollTopReader, consumePendingQueueListScrollTop } from '../store/queueUndo';
 import type { Track } from '../store/playerStoreTypes';
 
@@ -6,16 +6,16 @@ interface Args {
   queue: Track[];
   queueIndex: number;
   currentTrack: Track | null;
-  activeTab: string;
   queueListRef: React.RefObject<HTMLDivElement | null>;
   suppressNextAutoScrollRef: React.MutableRefObject<boolean>;
 }
 
-/** Queue auto-scroll: keeps the next track in view as playback progresses,
- *  publishes the list's scrollTop to the undo store, and restores any pending
- *  scrollTop snapshot (set when an undo restores a prior queue state). */
+/** Queue scroll-position bridge for undo: publishes the list's scrollTop to the
+ *  undo store and restores any pending scrollTop snapshot (set when an undo
+ *  restores a prior queue state). The "scroll the next track into view" path
+ *  lives in `QueueList` now that the list is virtualized (scrollToIndex). */
 export function useQueueAutoScroll({
-  queue, queueIndex, currentTrack, activeTab, queueListRef, suppressNextAutoScrollRef,
+  queue, queueIndex, currentTrack, queueListRef, suppressNextAutoScrollRef,
 }: Args) {
   useLayoutEffect(() => {
     registerQueueListScrollTopReader(() => queueListRef.current?.scrollTop);
@@ -31,21 +31,4 @@ export function useQueueAutoScroll({
     el.scrollTop = top;
     el.dispatchEvent(new Event('scroll', { bubbles: false }));
   }, [queue, queueIndex, currentTrack?.id, queueListRef, suppressNextAutoScrollRef]);
-
-  useEffect(function queueAutoScroll() {
-    if (suppressNextAutoScrollRef.current) {
-      suppressNextAutoScrollRef.current = false;
-      return;
-    }
-    if (!queueListRef.current || queueIndex < 0) return;
-    if (activeTab !== 'queue') return;
-    const songs = queueListRef.current!.querySelectorAll<HTMLElement>('[data-queue-idx]');
-    const nextSong = songs[queueIndex + 1];
-    if (!nextSong) return;
-    nextSong.scrollIntoView({ block: 'start', behavior: 'instant' });
-    requestAnimationFrame(() => {
-      queueListRef.current?.dispatchEvent(new Event('scroll', { bubbles: false }));
-    });
-  // eslint-disable-next-line react-hooks/exhaustive-deps
-  }, [currentTrack, activeTab]);
 }