perf(studio): virtualize timeline clip windows

packages/studio/src/player/components/Timeline.tsx

@@ -6,7 +6,6 @@ import { useExpandedTimelineElements } from "../hooks/useExpandedTimelineElement
 import { defaultTimelineTheme } from "./timelineTheme";
 import { useTimelineRangeSelection } from "./useTimelineRangeSelection";
 import { useTimelinePlayhead } from "./useTimelinePlayhead";
-import { useTimelineActiveClips } from "./useTimelineActiveClips";
 import { useTimelineZoom } from "./useTimelineZoom";
 import { useTimelineAssetDrop } from "./timelineDragDrop";
 import { TimelineEmptyState } from "./TimelineEmptyState";
@@ -42,9 +41,11 @@ import { useTimelineSelectionLifecycle } from "./useTimelineSelectionLifecycle";
 import { useTimelineShiftModifier } from "./useTimelineShiftModifier";
 import { useTimelineTicks } from "./useTimelineTicks";
 import { getTimelineElementIndexes } from "../lib/timelineElementIndexes";
+import { getTimelineElementIdentity } from "../lib/timelineElementHelpers";
 import { useTimelineRowVirtualization } from "./useTimelineRowVirtualization";
+import { useTimelineClipRenderWindow } from "./useTimelineClipRenderWindow";
+import { useTimelineActiveClips } from "./useTimelineActiveClips";
 
-// Re-export pure utilities so existing imports from "./Timeline" still resolve.
 export {
   shouldAutoScrollTimeline,
   getTimelineScrollLeftForZoomTransition,
@@ -126,9 +127,8 @@ export const Timeline = memo(function Timeline({
   const selectedElementId = usePlayerStore((s) => s.selectedElementId);
   const selectedElementIds = usePlayerStore((s) => s.selectedElementIds);
   const clipRevealRequest = usePlayerStore((s) => s.clipRevealRequest);
+  const focusedEaseSegment = usePlayerStore((s) => s.focusedEaseSegment);
   const gsapAnimations = usePlayerStore((s) => s.gsapAnimations);
-  // Label mode = comp has keyframed clips (not just when expanded): keeps the layer
-  // disclosure + property column visible and reserves a GUTTER before 0s (Figma).
   const hasKeyframedClips = useMemo(
     () => hasKeyframedTimelineClips(gsapAnimations),
     [gsapAnimations],
@@ -163,7 +163,6 @@ export const Timeline = memo(function Timeline({
     containerRef.current = el;
   }, []);
 
-  // Last horizontal scroll offset, restored across the post-edit iframe reload (pinned zoom).
   const lastScrollLeftRef = useRef(0);
 
   const effectiveDuration = useMemo(
@@ -320,28 +319,50 @@ export const Timeline = memo(function Timeline({
       toggleSelectedKeyframe,
     });
 
-  const {
-    pps,
-    fitPps,
-    displayContentWidth,
-    displayDuration,
-    clipStateVersion,
-    zoomModeRef,
-    manualZoomPercentRef,
-  } = useTimelineGeometry({
-    viewportWidth: viewport.clientWidth,
-    effectiveDuration,
-    zoomMode,
-    manualZoomPercent,
-    ppsRef,
-    fitPpsRef,
-    draggedClip,
-    resizingClip,
-    expandedElements,
-    isDragging,
-    scrollRef,
-    lastScrollLeftRef,
+  const { pps, fitPps, displayContentWidth, displayDuration, zoomModeRef, manualZoomPercentRef } =
+    useTimelineGeometry({
+      viewportWidth: viewport.clientWidth,
+      effectiveDuration,
+      zoomMode,
+      manualZoomPercent,
+      ppsRef,
+      fitPpsRef,
+      draggedClip,
+      resizingClip,
+      expandedElements,
+      isDragging,
+      scrollRef,
+      lastScrollLeftRef,
+      contentOrigin,
+    });
+  const { clipIndex, renderTimeRange, pinnedClipIdentities } = useTimelineClipRenderWindow({
+    tracks,
+    viewport,
+    pixelsPerSecond: pps,
     contentOrigin,
+    duration: displayDuration,
+    selectedElementId: selectedElementId ?? undefined,
+    draggedElementId: draggedClip ? getTimelineElementIdentity(draggedClip.element) : undefined,
+    resizingElementId: resizingClip ? getTimelineElementIdentity(resizingClip.element) : undefined,
+    revealElementId: clipRevealRequest?.elementId,
+    focusedEaseElementId: focusedEaseSegment?.elementId,
+    clipContextMenuElementId: clipContextMenu
+      ? getTimelineElementIdentity(clipContextMenu.element)
+      : undefined,
+    keyframeContextMenuElementId: kfContextMenu
+      ? getTimelineElementIdentity(kfContextMenu.element)
+      : undefined,
+    scrollRef,
+    elements: expandedElements,
+    rowGeometry: displayLayout.rowGeometry,
+    allowHorizontalReveal: zoomMode === "manual",
+    sessionEpoch,
+  });
+  useTimelineActiveClips({
+    scrollRef,
+    currentTime,
+    clipStateVersion: renderTimeRange,
+    elementStateVersion: expandedElements,
   });
 
   const laneGapStrips = useTimelineGapHighlights({
@@ -376,11 +397,6 @@ export const Timeline = memo(function Timeline({
     onSeek,
     contentOrigin,
   });
-  useTimelineActiveClips({
-    scrollRef,
-    currentTime,
-    clipStateVersion,
-  });
   const { razorGuideX, updateRazorGuide, clearRazorGuide, splitAllAtPointer } =
     useTimelineRazorInteraction({
       active: activeTool === "razor",
@@ -422,8 +438,12 @@ export const Timeline = memo(function Timeline({
     setRangeSelection(null),
   );
 
-  const { major, minor } = useTimelineTicks(displayDuration, pps, timeDisplayMode);
-  const majorTickInterval = major.length >= 2 ? major[1] - major[0] : effectiveDuration;
+  const { major, minor, majorTickInterval } = useTimelineTicks(
+    displayDuration,
+    pps,
+    timeDisplayMode,
+    rowVirtualizationActive ? renderTimeRange : undefined,
+  );
 
   const getPreviewElement = useCallback(
     (element: TimelineElement): TimelineElement => getTimelinePreviewElement(element, resizingClip),
@@ -500,6 +520,9 @@ export const Timeline = memo(function Timeline({
           rowGeometry={displayLayout.rowGeometry}
           virtualRows={virtualRows}
           rowsVirtualized={rowVirtualizationActive}
+          clipIndex={clipIndex}
+          renderTimeRange={renderTimeRange}
+          pinnedClipIdentities={pinnedClipIdentities}
           trackOrder={trackOrder}
           tracks={tracks}
           trackStyles={trackStyles}
@@ -513,7 +536,7 @@ export const Timeline = memo(function Timeline({
           blockedClipRef={blockedClipRef}
           suppressClickRef={suppressClickRef}
           scrollRef={scrollRef}
-          renderClipContent={renderClipContent}
+          renderClipContent={viewport.isScrolling ? undefined : renderClipContent}
           renderClipOverlay={renderClipOverlay}
           playheadRef={playheadRef}
           onDrillDown={onDrillDown}

packages/studio/src/player/components/Timeline.virtualization.test.tsx

@@ -57,7 +57,25 @@ afterAll(() => {
   document.body.innerHTML = "";
 });
 
-describe("Timeline row virtualization", () => {
+/**
+ * The virtualized list only mounts rows/clips after its ResizeObserver and the
+ * follow-up layout effect have both flushed, which is more than one React tick.
+ * A fixed number of flushes is a coin flip once the rest of the suite is
+ * competing for workers, so wait for the DOM the assertions actually need.
+ */
+async function settleUntil(predicate: () => boolean, tries = 60): Promise<void> {
+  for (let attempt = 0; attempt < tries; attempt++) {
+    if (predicate()) return;
+    await act(async () => {
+      await new Promise<void>((resolve) => requestAnimationFrame(() => resolve()));
+    });
+  }
+}
+
+// These tests mount 500-10,000 timeline elements and settle the virtualizer,
+// which lands right on the 5s default once the rest of the suite is competing
+// for workers. The generous ceiling is a flake guard, not an expected runtime.
+describe("Timeline row virtualization", { timeout: 30_000 }, () => {
   it("keeps a zero-size first render bounded while the feature flag is enabled", async () => {
     clientWidth = 0;
     clientHeight = 0;
@@ -89,7 +107,60 @@ describe("Timeline row virtualization", () => {
 
     act(() => root.unmount());
     usePlayerStore.getState().reset();
-  }, 10_000);
+  });
+
+  it("defers rich clip content while scrolling without replacing the clip shell", async () => {
+    const [{ Timeline }, { usePlayerStore }] = await Promise.all([
+      import("./Timeline"),
+      import("../store/playerStore"),
+    ]);
+    usePlayerStore.setState({
+      duration: 60,
+      timelineReady: true,
+      selectedElementId: "clip-0",
+      elements: [{ id: "clip-0", label: "Clip 0", tag: "div", start: 0, duration: 10, track: 0 }],
+    });
+
+    const host = document.createElement("div");
+    document.body.append(host);
+    const root = createRoot(host);
+    try {
+      await act(async () =>
+        root.render(
+          React.createElement(Timeline, {
+            renderClipContent: () => React.createElement("span", { "data-rich-content": true }),
+          }),
+        ),
+      );
+      await act(async () => {});
+      await act(async () => {
+        await new Promise((resolve) => setTimeout(resolve, 110));
+      });
+
+      const scroller = host.querySelector<HTMLElement>("[data-timeline-scroll-viewport]");
+      const clip = host.querySelector<HTMLElement>('[data-el-id="clip-0"]');
+      expect(scroller).not.toBeNull();
+      expect(clip).not.toBeNull();
+      expect(clip?.title).toBe("Clip 0 • 0.0s – 10.0s");
+      expect(host.querySelector("[data-rich-content]")).not.toBeNull();
+
+      await act(async () => {
+        scroller?.dispatchEvent(new Event("scroll"));
+        await new Promise<void>((resolve) => requestAnimationFrame(() => resolve()));
+      });
+      expect(host.querySelector('[data-el-id="clip-0"]')).toBe(clip);
+      expect(host.querySelector("[data-rich-content]")).toBeNull();
+
+      await act(async () => {
+        await new Promise((resolve) => setTimeout(resolve, 110));
+      });
+      expect(host.querySelector('[data-el-id="clip-0"]')).toBe(clip);
+      expect(host.querySelector("[data-rich-content]")).not.toBeNull();
+    } finally {
+      act(() => root.unmount());
+      usePlayerStore.getState().reset();
+    }
+  });
 
   it("mounts a bounded list range over the full geometry height", async () => {
     const [{ Timeline }, { usePlayerStore }, { getTimelineCanvasHeight, TRACK_H }] =
@@ -101,6 +172,8 @@ describe("Timeline row virtualization", () => {
     usePlayerStore.setState({
       duration: 60,
       timelineReady: true,
+      // Repeated fixture shape intentionally contrasts row and clip windowing scales.
+      // fallow-ignore-next-line code-duplication
       elements: Array.from({ length: 1_000 }, (_, track) => ({
         id: `clip-${track}`,
         tag: "div",
@@ -116,6 +189,11 @@ describe("Timeline row virtualization", () => {
     await act(async () => root.render(React.createElement(Timeline, { sessionEpoch: 3 })));
     await act(async () => {});
 
+    await settleUntil(
+      () =>
+        (host.querySelector('[role="list"]')?.querySelectorAll('[role="listitem"]').length ?? 0) >
+        0,
+    );
     const list = host.querySelector<HTMLElement>('[role="list"]');
     const rows = list?.querySelectorAll('[role="listitem"]') ?? [];
     expect(rows.length).toBeGreaterThan(0);
@@ -143,5 +221,77 @@ describe("Timeline row virtualization", () => {
 
     act(() => root.unmount());
     usePlayerStore.getState().reset();
-  }, 10_000);
+  });
+
+  it("windows clips and ruler cells while retaining an off-window selected clip", async () => {
+    const [{ Timeline }, { usePlayerStore }, { TIMELINE_VIEWPORT_BUDGETS }] = await Promise.all([
+      import("./Timeline"),
+      import("../store/playerStore"),
+      import("../lib/timelineViewportBudgets"),
+    ]);
+    usePlayerStore.setState({
+      duration: 1_000,
+      timelineReady: true,
+      zoomMode: "manual",
+      manualZoomPercent: 2_000,
+      selectedElementId: "clip-490",
+      selectedElementIds: new Set(["clip-490"]),
+      // Repeated fixture shape intentionally contrasts row and clip windowing scales.
+      // fallow-ignore-next-line code-duplication
+      elements: Array.from({ length: 500 }, (_, index) => ({
+        id: `clip-${index}`,
+        tag: "div",
+        start: index * 2,
+        duration: 1,
+        track: 0,
+      })),
+    });
+
+    const host = document.createElement("div");
+    document.body.append(host);
+    const root = createRoot(host);
+    await act(async () => root.render(React.createElement(Timeline, { sessionEpoch: 4 })));
+    await act(async () => {});
+
+    await settleUntil(() => host.querySelectorAll("[data-clip]").length > 1);
+    const initialClips = [...host.querySelectorAll<HTMLElement>("[data-clip]")];
+    const initialGridCells = host.querySelectorAll("[data-timeline-grid-cell]");
+    expect(initialClips.length).toBeGreaterThan(1);
+    expect(initialClips.length).toBeLessThanOrEqual(
+      TIMELINE_VIEWPORT_BUDGETS.maxMountedClipRootsPerRow + 1,
+    );
+    expect(initialGridCells.length).toBeLessThan(100);
+    expect(host.querySelector('[data-el-id="clip-490"]')).not.toBeNull();
+    const initialWindowIds = initialClips.map((clip) => clip.dataset.elId);
+
+    const scroller = host.querySelector<HTMLElement>("[data-timeline-scroll-viewport]");
+    expect(scroller).not.toBeNull();
+    if (scroller) {
+      scroller.scrollLeft = 8_000;
+      await act(async () => {
+        scroller.dispatchEvent(new Event("scroll"));
+        await new Promise<void>((resolve) => requestAnimationFrame(() => resolve()));
+      });
+    }
+
+    const scrolledClips = [...host.querySelectorAll<HTMLElement>("[data-clip]")];
+    expect(scrolledClips.map((clip) => clip.dataset.elId)).not.toEqual(initialWindowIds);
+    expect(scrolledClips.length).toBeLessThanOrEqual(
+      TIMELINE_VIEWPORT_BUDGETS.maxMountedClipRootsPerRow + 1,
+    );
+    expect(host.querySelector('[data-el-id="clip-490"]')).not.toBeNull();
+    expect(host.querySelectorAll("[data-timeline-grid-cell]").length).toBeLessThan(100);
+
+    await act(async () => usePlayerStore.getState().requestClipReveal("clip-300"));
+    await act(async () => {
+      await new Promise<void>((resolve) => requestAnimationFrame(() => resolve()));
+    });
+    await act(async () => {});
+    expect(usePlayerStore.getState().clipRevealRequest).toBeNull();
+    expect(document.activeElement?.getAttribute("data-el-id")).toBe("clip-300");
+    expect(host.querySelector('[data-el-id="clip-490"]')).not.toBeNull();
+
+    act(() => root.unmount());
+    usePlayerStore.getState().reset();
+  });
 });