feat(editor): AnimationController for scrollToContent (#11553)

---------

Signed-off-by: Mark Tolmacs <mark@lazycat.hu>
Co-authored-by: dwelle <5153846+dwelle@users.noreply.github.com>

packages/common/src/utils.ts

@@ -204,135 +204,6 @@ export const easeOut = (k: number) => {
   return 1 - Math.pow(1 - k, 4);
 };
 
-const easeOutInterpolate = (from: number, to: number, progress: number) => {
-  return (to - from) * easeOut(progress) + from;
-};
-
-/**
- * Animates values from `fromValues` to `toValues` using the requestAnimationFrame API.
- * Executes the `onStep` callback on each step with the interpolated values.
- * Returns a function that can be called to cancel the animation.
- *
- * @example
- * // Example usage:
- * const fromValues = { x: 0, y: 0 };
- * const toValues = { x: 100, y: 200 };
- * const onStep = ({x, y}) => {
- *   setState(x, y)
- * };
- * const onCancel = () => {
- *   console.log("Animation canceled");
- * };
- *
- * const cancelAnimation = easeToValuesRAF({
- *   fromValues,
- *   toValues,
- *   onStep,
- *   onCancel,
- * });
- *
- * // To cancel the animation:
- * cancelAnimation();
- */
-export const easeToValuesRAF = <
-  T extends Record<keyof T, number>,
-  K extends keyof T,
->({
-  fromValues,
-  toValues,
-  onStep,
-  duration = 250,
-  interpolateValue,
-  onStart,
-  onEnd,
-  onCancel,
-}: {
-  fromValues: T;
-  toValues: T;
-  /**
-   * Interpolate a single value.
-   * Return undefined to be handled by the default interpolator.
-   */
-  interpolateValue?: (
-    fromValue: number,
-    toValue: number,
-    /** no easing applied  */
-    progress: number,
-    key: K,
-  ) => number | undefined;
-  onStep: (values: T) => void;
-  duration?: number;
-  onStart?: () => void;
-  onEnd?: () => void;
-  onCancel?: () => void;
-}) => {
-  let canceled = false;
-  let frameId = 0;
-  let startTime: number;
-
-  function step(timestamp: number) {
-    if (canceled) {
-      return;
-    }
-    if (startTime === undefined) {
-      startTime = timestamp;
-      onStart?.();
-    }
-
-    const elapsed = Math.min(timestamp - startTime, duration);
-    const factor = easeOut(elapsed / duration);
-
-    const newValues = {} as T;
-
-    Object.keys(fromValues).forEach((key) => {
-      const _key = key as keyof T;
-      const result = ((toValues[_key] - fromValues[_key]) * factor +
-        fromValues[_key]) as T[keyof T];
-      newValues[_key] = result;
-    });
-
-    onStep(newValues);
-
-    if (elapsed < duration) {
-      const progress = elapsed / duration;
-
-      const newValues = {} as T;
-
-      Object.keys(fromValues).forEach((key) => {
-        const _key = key as K;
-        const startValue = fromValues[_key];
-        const endValue = toValues[_key];
-
-        let result;
-
-        result = interpolateValue
-          ? interpolateValue(startValue, endValue, progress, _key)
-          : easeOutInterpolate(startValue, endValue, progress);
-
-        if (result == null) {
-          result = easeOutInterpolate(startValue, endValue, progress);
-        }
-
-        newValues[_key] = result as T[K];
-      });
-      onStep(newValues);
-
-      frameId = window.requestAnimationFrame(step);
-    } else {
-      onStep(toValues);
-      onEnd?.();
-    }
-  }
-
-  frameId = window.requestAnimationFrame(step);
-
-  return () => {
-    onCancel?.();
-    canceled = true;
-    window.cancelAnimationFrame(frameId);
-  };
-};
-
 // https://github.com/lodash/lodash/blob/es/chunk.js
 export const chunk = <T extends any>(
   array: readonly T[],

packages/excalidraw/components/App.tsx

@@ -77,11 +77,9 @@ import {
   updateObject,
   updateActiveTool,
   isTransparent,
-  easeToValuesRAF,
   muteFSAbortError,
   isTestEnv,
   isDevEnv,
-  easeOut,
   updateStable,
   addEventListener,
   normalizeEOL,
@@ -203,7 +201,6 @@ import {
   cropElement,
   wrapText,
   isElementLink,
-  parseElementLinkFromURL,
   isMeasureTextSupported,
   normalizeText,
   measureText,
@@ -264,6 +261,7 @@ import {
   getActiveTextElement,
   isEligibleFrameChildType,
   getBindingStrategyForDraggingBindingElementEndpoints,
+  parseElementLinkFromURL,
 } from "@excalidraw/element";
 
 import type { GlobalPoint, LocalPoint, Radians } from "@excalidraw/math";
@@ -331,7 +329,7 @@ import {
   actionToggleCropEditor,
 } from "../actions";
 import { actionWrapTextInContainer } from "../actions/actionBoundText";
-import { actionToggleHandTool, zoomToFit } from "../actions/actionCanvas";
+import { actionToggleHandTool } from "../actions/actionCanvas";
 import { actionPaste } from "../actions/actionClipboard";
 import { actionCopyElementLink } from "../actions/actionElementLink";
 import { actionUnlockAllElements } from "../actions/actionElementLock";
@@ -413,6 +411,11 @@ import {
   isGridModeEnabled,
 } from "../snapping";
 import { Renderer } from "../scene/Renderer";
+import {
+  type ScrollToContentOptions,
+  SCROLL_TO_CONTENT_ANIMATION_KEY,
+  scrollToElements,
+} from "../scroll";
 import {
   setEraserCursor,
   setCursor,
@@ -425,16 +428,12 @@ import { withBatchedUpdates, withBatchedUpdatesThrottled } from "../reactUtils";
 import { isPointHittingTextAutoResizeHandle } from "../textAutoResizeHandle";
 import { textWysiwyg } from "../wysiwyg/textWysiwyg";
 import { isOverScrollBars } from "../scene/scrollbars";
-
 import { isMaybeMermaidDefinition } from "../mermaid";
-
 import { LassoTrail } from "../lasso";
-
 import { EraserTrail } from "../eraser";
-
 import { getShortcutKey } from "../shortcut";
-
 import { tryParseSpreadsheet } from "../charts";
+import { AnimationController } from "../renderer/animation";
 
 import ConvertElementTypePopup, {
   getConversionTypeFromElements,
@@ -4341,148 +4340,60 @@ class App extends React.Component<AppProps, AppState> {
     });
   };
 
-  private cancelInProgressAnimation: (() => void) | null = null;
-
   scrollToContent = (
-    /**
+    target?:
-     * target to scroll to
-     *
-     * - string - id of element or group, or url containing elementLink
-     * - ExcalidrawElement | ExcalidrawElement[] - element(s) objects
-     */
-    target:
       | string
       | ExcalidrawElement
-      | readonly ExcalidrawElement[] = this.scene.getNonDeletedElements(),
+      | readonly NonDeletedExcalidrawElement[],
-    opts?: (
+    opts?: ScrollToContentOptions,
-      | {
-          fitToContent?: boolean;
-          fitToViewport?: never;
-          viewportZoomFactor?: number;
-          animate?: boolean;
-          duration?: number;
-        }
-      | {
-          fitToContent?: never;
-          fitToViewport?: boolean;
-          /** when fitToViewport=true, how much screen should the content cover,
-           * between 0.1 (10%) and 1 (100%)
-           */
-          viewportZoomFactor?: number;
-          animate?: boolean;
-          duration?: number;
-        }
-    ) & {
-      minZoom?: number;
-      maxZoom?: number;
-      canvasOffsets?: Offsets;
-    },
   ) => {
+    let elements: readonly NonDeleted<ExcalidrawElement>[];
     if (typeof target === "string") {
-      let id: string | null;
+      const id = isElementLink(target)
-      if (isElementLink(target)) {
+        ? parseElementLinkFromURL(target)
-        id = parseElementLinkFromURL(target);
+        : target;
-      } else {
+      elements = id ? this.scene.getElementsFromId(id) : [];
-        id = target;
+    } else if (Array.isArray(target)) {
-      }
+      elements = target;
-      if (id) {
+    } else if (target) {
-        const elements = this.scene.getElementsFromId(id);
+      elements = [target as NonDeleted<ExcalidrawElement>];
+    } else {
+      elements = this.scene.getNonDeletedElements();
+    }
 
-        if (elements?.length) {
+    if (!elements.length) {
-          this.scrollToContent(elements, {
+      if (typeof target === "string" && isElementLink(target)) {
-            fitToContent: opts?.fitToContent ?? true,
+        this.setState({
-            animate: opts?.animate ?? true,
+          toast: {
-          });
+            message: t("elementLink.notFound"),
-        } else if (isElementLink(target)) {
+            duration: 3000,
-          this.setState({
+            closable: true,
-            toast: {
+          },
-              message: t("elementLink.notFound"),
+        });
-              duration: 3000,
-              closable: true,
-            },
-          });
-        }
       }
+
       return;
     }
 
-    this.cancelInProgressAnimation?.();
+    // Navigating to an element by id or element-link defaults to zooming the
-
+    // element into view, animated — matching the historical element-link
-    // convert provided target into ExcalidrawElement[] if necessary
+    // behavior — unless the caller opts out.
-    const targetElements = Array.isArray(target) ? target : [target];
+    const resolvedOpts =
-
+      typeof target === "string"
-    let zoom = this.state.zoom;
+        ? {
-    let scrollX = this.state.scrollX;
+            ...opts,
-    let scrollY = this.state.scrollY;
+            fitToViewport: undefined,
-
+            fitToContent: opts?.fitToContent ?? true,
-    if (opts?.fitToContent || opts?.fitToViewport) {
+            animate: opts?.animate ?? true,
-      const { appState } = zoomToFit({
-        canvasOffsets: opts.canvasOffsets,
-        targetElements,
-        appState: this.state,
-        fitToViewport: !!opts?.fitToViewport,
-        viewportZoomFactor: opts?.viewportZoomFactor,
-        minZoom: opts?.minZoom,
-        maxZoom: opts?.maxZoom,
-      });
-      zoom = appState.zoom;
-      scrollX = appState.scrollX;
-      scrollY = appState.scrollY;
-    } else {
-      // compute only the viewport location, without any zoom adjustment
-      const scroll = calculateScrollCenter(targetElements, this.state);
-      scrollX = scroll.scrollX;
-      scrollY = scroll.scrollY;
-    }
-
-    // when animating, we use RequestAnimationFrame to prevent the animation
-    // from slowing down other processes
-    if (opts?.animate) {
-      const origScrollX = this.state.scrollX;
-      const origScrollY = this.state.scrollY;
-      const origZoom = this.state.zoom.value;
-
-      const cancel = easeToValuesRAF({
-        fromValues: {
-          scrollX: origScrollX,
-          scrollY: origScrollY,
-          zoom: origZoom,
-        },
-        toValues: { scrollX, scrollY, zoom: zoom.value },
-        interpolateValue: (from, to, progress, key) => {
-          // for zoom, use different easing
-          if (key === "zoom") {
-            return from * Math.pow(to / from, easeOut(progress));
           }
-          // handle using default
+        : opts;
-          return undefined;
-        },
-        onStep: ({ scrollX, scrollY, zoom }) => {
-          this.setState({
-            scrollX,
-            scrollY,
-            zoom: { value: zoom },
-          });
-        },
-        onStart: () => {
-          this.setState({ shouldCacheIgnoreZoom: true });
-        },
-        onEnd: () => {
-          this.setState({ shouldCacheIgnoreZoom: false });
-        },
-        onCancel: () => {
-          this.setState({ shouldCacheIgnoreZoom: false });
-        },
-        duration: opts?.duration ?? 500,
-      });
 
-      this.cancelInProgressAnimation = () => {
+    scrollToElements(
-        cancel();
+      this.state,
-        this.cancelInProgressAnimation = null;
+      elements,
-      };
+      this.setState.bind(this),
-    } else {
+      resolvedOpts,
-      this.setState({ scrollX, scrollY, zoom });
+    );
-    }
   };
 
   private maybeUnfollowRemoteUser = () => {
@@ -4495,7 +4406,8 @@ class App extends React.Component<AppProps, AppState> {
   private translateCanvas: React.Component<any, AppState>["setState"] = (
     state,
   ) => {
-    this.cancelInProgressAnimation?.();
+    AnimationController.cancel(SCROLL_TO_CONTENT_ANIMATION_KEY);
+    this.setState({ shouldCacheIgnoreZoom: false });
     this.maybeUnfollowRemoteUser();
     this.setState(state);
   };

packages/excalidraw/renderer/animation.ts

@@ -123,4 +123,9 @@ export class AnimationController {
     AnimationController.animations.delete(key);
     AnimationController.cancelScheduledFrameIfIdle();
   }
+
+  static reset() {
+    AnimationController.animations.clear();
+    AnimationController.cancelScheduledFrame();
+  }
 }

packages/excalidraw/scroll.ts

@@ -0,0 +1,147 @@
+import { easeOut } from "@excalidraw/common";
+import { clamp } from "@excalidraw/math";
+
+import type { ExcalidrawElement } from "@excalidraw/element/types";
+
+import { zoomToFit } from "./actions/actionCanvas";
+import { AnimationController } from "./renderer/animation";
+import { calculateScrollCenter } from "./scene/scroll";
+
+import type { AppState, NormalizedZoomValue, Offsets } from "./types";
+
+export const SCROLL_TO_CONTENT_ANIMATION_KEY = "animateScrollToContent";
+
+/** default duration of the scroll/zoom animation, in milliseconds */
+const DEFAULT_ANIMATION_DURATION = 500;
+
+export type ScrollToContentOptions = (
+  | {
+      fitToContent?: boolean;
+      fitToViewport?: never;
+      viewportZoomFactor?: number;
+      animate?: boolean;
+      duration?: number;
+    }
+  | {
+      fitToContent?: never;
+      fitToViewport?: boolean;
+      /** when fitToViewport=true, how much screen should the content cover,
+       * between 0.1 (10%) and 1 (100%) */
+      viewportZoomFactor?: number;
+      animate?: boolean;
+      duration?: number;
+    }
+) & {
+  minZoom?: number;
+  maxZoom?: number;
+  canvasOffsets?: Offsets;
+};
+
+type Viewport = Pick<AppState, "scrollX" | "scrollY" | "zoom">;
+
+/**
+ * Scrolls (and optionally zooms) the viewport so that the given target is in
+ * view, optionally animating the transition.
+ */
+export const scrollToElements = (
+  state: AppState,
+  target: readonly ExcalidrawElement[],
+  onFrame: (
+    state: Pick<
+      AppState,
+      "scrollX" | "scrollY" | "zoom" | "shouldCacheIgnoreZoom"
+    >,
+  ) => void,
+  opts?: ScrollToContentOptions,
+) => {
+  AnimationController.cancel(SCROLL_TO_CONTENT_ANIMATION_KEY);
+
+  const viewport = getTargetViewport(state, target, opts);
+
+  if (opts?.animate) {
+    animateToViewport(
+      state,
+      viewport,
+      opts.duration ?? DEFAULT_ANIMATION_DURATION,
+      onFrame,
+    );
+  } else {
+    // no animation: jump straight to the target. Re-enable zoom caching in
+    // case we just cancelled an in-flight animation that had suppressed it.
+    onFrame({ ...viewport, shouldCacheIgnoreZoom: false });
+  }
+};
+
+/** Computes the viewport (scroll + zoom) that brings the target elements into
+ * view, based on the requested fit behavior. */
+const getTargetViewport = (
+  state: AppState,
+  targetElements: readonly ExcalidrawElement[],
+  opts?: ScrollToContentOptions,
+): Viewport => {
+  if (opts?.fitToContent || opts?.fitToViewport) {
+    const { appState } = zoomToFit({
+      canvasOffsets: opts.canvasOffsets,
+      targetElements,
+      appState: state,
+      fitToViewport: !!opts.fitToViewport,
+      viewportZoomFactor: opts.viewportZoomFactor,
+      minZoom: opts.minZoom,
+      maxZoom: opts.maxZoom,
+    });
+
+    return {
+      scrollX: appState.scrollX,
+      scrollY: appState.scrollY,
+      zoom: appState.zoom,
+    };
+  }
+
+  // keep the current zoom, only recenter the viewport on the target
+  const { scrollX, scrollY } = calculateScrollCenter(targetElements, state);
+
+  return { scrollX, scrollY, zoom: state.zoom };
+};
+
+/** Eases the viewport from its current position to `target` over `duration`,
+ * driving the transition through the shared AnimationController so it doesn't
+ * slow down other processes. */
+const animateToViewport = (
+  from: Pick<AppState, "scrollX" | "scrollY" | "zoom">,
+  target: Viewport,
+  duration: number,
+  onFrame: (
+    state: Pick<
+      AppState,
+      "scrollX" | "scrollY" | "zoom" | "shouldCacheIgnoreZoom"
+    >,
+  ) => void,
+) => {
+  AnimationController.start<{ elapsed: number }>(
+    SCROLL_TO_CONTENT_ANIMATION_KEY,
+    ({ deltaTime, state }) => {
+      const elapsed = (state?.elapsed ?? 0) + deltaTime;
+      const progress = Math.min(elapsed / duration, 1);
+      const factor = easeOut(clamp(progress, 0, 1));
+
+      onFrame({
+        shouldCacheIgnoreZoom: progress < 1, // ignore zoom caching while animating
+        scrollX: from.scrollX + (target.scrollX - from.scrollX) * factor,
+        scrollY: from.scrollY + (target.scrollY - from.scrollY) * factor,
+        // zoom interpolates geometrically so the transition feels natural
+        zoom: {
+          value: (from.zoom.value *
+            Math.pow(
+              target.zoom.value / from.zoom.value,
+              factor,
+            )) as NormalizedZoomValue,
+        },
+      });
+
+      // returning a falsy value signals the AnimationController to remove the
+      // animation; otherwise it would keep ticking (and calling onFrame) every
+      // frame forever after reaching the target
+      return progress < 1 ? { elapsed } : null;
+    },
+  );
+};

packages/excalidraw/tests/fitToContent.test.tsx

@@ -1,20 +1,62 @@
 import React from "react";
-import { vi } from "vitest";
 
 import { Excalidraw } from "../index";
+import { AnimationController } from "../renderer/animation";
+import { SCROLL_TO_CONTENT_ANIMATION_KEY } from "../scroll";
 
 import { API } from "./helpers/api";
 import { act, render } from "./test-utils";
 
 const { h } = window;
 
-const waitForNextAnimationFrame = () => {
+/**
+ * The scroll/zoom animation is driven by `AnimationController`. With render
+ * throttling enabled (see the `beforeEach` below) it schedules frames via
+ * `requestAnimationFrame`, advancing the easing based on elapsed wall-clock
+ * time. We use a very long animation `duration` (see `LONG_ANIMATION_DURATION`)
+ * so it can never complete while we sample it, and let a few frames pass
+ * between samples so the easing makes observable (but partial) progress.
+ */
+const LONG_ANIMATION_DURATION = 1_000_000;
+
+const waitForAnimationProgress = (frames = 4) => {
   return act(
     () =>
-      new Promise((resolve) => {
+      new Promise<void>((resolve) => {
-        requestAnimationFrame(() => {
+        let remaining = frames;
-          requestAnimationFrame(resolve);
+        const step = () => {
-        });
+          if (--remaining <= 0) {
+            resolve();
+          } else {
+            requestAnimationFrame(step);
+          }
+        };
+        requestAnimationFrame(step);
+      }),
+  );
+};
+
+/**
+ * Polls until the scroll/zoom animation has removed itself from the
+ * `AnimationController` (i.e. it ran to completion), or until `maxFrames`
+ * elapses as a safety net so a regression can't hang the suite.
+ */
+const waitForAnimationToStop = (maxFrames = 200) => {
+  return act(
+    () =>
+      new Promise<void>((resolve) => {
+        let remaining = maxFrames;
+        const check = () => {
+          if (
+            !AnimationController.running(SCROLL_TO_CONTENT_ANIMATION_KEY) ||
+            --remaining <= 0
+          ) {
+            resolve();
+          } else {
+            requestAnimationFrame(check);
+          }
+        };
+        requestAnimationFrame(check);
       }),
   );
 };
@@ -77,6 +119,34 @@ describe("fitToContent", () => {
     expect(h.state.zoom.value).toBeLessThanOrEqual(0.1);
   });
 
+  it("should default to fitToContent when scrolling to an element by id", async () => {
+    await render(<Excalidraw />);
+
+    h.state.width = 10;
+    h.state.height = 10;
+
+    const rectElement = API.createElement({
+      width: 50,
+      height: 100,
+      x: 50,
+      y: 100,
+    });
+
+    API.setElements([rectElement]);
+
+    expect(h.state.zoom.value).toBe(1);
+
+    act(() => {
+      // navigating by element id (a string target) should zoom-to-fit by
+      // default, even though no `fitToContent` option was passed
+      h.app.scrollToContent(rectElement.id, { animate: false });
+    });
+
+    // element is 10x taller than the viewport, so fit-to-content should
+    // drop the zoom to <= 1/10
+    expect(h.state.zoom.value).toBeLessThanOrEqual(0.1);
+  });
+
   it("should scroll the viewport to the selected element", async () => {
     await render(<Excalidraw />);
 
@@ -109,11 +179,16 @@ describe("fitToContent", () => {
 
 describe("fitToContent animated", () => {
   beforeEach(() => {
-    vi.spyOn(window, "requestAnimationFrame");
+    // pace the animation via requestAnimationFrame instead of a tight
+    // setTimeout(0) loop, which would otherwise starve the test's own timers
+    window.EXCALIDRAW_THROTTLE_RENDER = true;
   });
 
   afterEach(() => {
-    vi.restoreAllMocks();
+    window.EXCALIDRAW_THROTTLE_RENDER = undefined;
+    // stop any in-flight scroll/zoom animation so it doesn't keep ticking on
+    // the unmounted component and leak into the next test via the singleton
+    AnimationController.reset();
   });
 
   it("should ease scroll the viewport to the selected element", async () => {
@@ -130,17 +205,18 @@ describe("fitToContent animated", () => {
     });
 
     act(() => {
-      h.app.scrollToContent(rectElement, { animate: true });
+      h.app.scrollToContent(rectElement, {
+        animate: true,
+        duration: LONG_ANIMATION_DURATION,
+      });
     });
 
-    expect(window.requestAnimationFrame).toHaveBeenCalled();
+    // the animation hasn't progressed yet, so we're still at the origin
-
-    // Since this is an animation, we expect values to change through time.
-    // We'll verify that the scroll values change at 50ms and 100ms
     expect(h.state.scrollX).toBe(0);
     expect(h.state.scrollY).toBe(0);
 
-    await waitForNextAnimationFrame();
+    // Since this is an animation, we expect values to change through time.
+    await waitForAnimationProgress();
 
     const prevScrollX = h.state.scrollX;
     const prevScrollY = h.state.scrollY;
@@ -148,7 +224,7 @@ describe("fitToContent animated", () => {
     expect(h.state.scrollX).not.toBe(0);
     expect(h.state.scrollY).not.toBe(0);
 
-    await waitForNextAnimationFrame();
+    await waitForAnimationProgress();
 
     expect(h.state.scrollX).not.toBe(prevScrollX);
     expect(h.state.scrollY).not.toBe(prevScrollY);
@@ -171,12 +247,14 @@ describe("fitToContent animated", () => {
     expect(h.state.scrollY).toBe(0);
 
     act(() => {
-      h.app.scrollToContent(rectElement, { animate: true, fitToContent: true });
+      h.app.scrollToContent(rectElement, {
+        animate: true,
+        fitToContent: true,
+        duration: LONG_ANIMATION_DURATION,
+      });
     });
 
-    expect(window.requestAnimationFrame).toHaveBeenCalled();
+    await waitForAnimationProgress();
-
-    await waitForNextAnimationFrame();
 
     const prevScrollX = h.state.scrollX;
     const prevScrollY = h.state.scrollY;
@@ -184,9 +262,48 @@ describe("fitToContent animated", () => {
     expect(h.state.scrollX).not.toBe(0);
     expect(h.state.scrollY).not.toBe(0);
 
-    await waitForNextAnimationFrame();
+    await waitForAnimationProgress();
 
     expect(h.state.scrollX).not.toBe(prevScrollX);
     expect(h.state.scrollY).not.toBe(prevScrollY);
   });
+
+  it("should stop ticking and settle on the target once complete", async () => {
+    await render(<Excalidraw />);
+
+    h.state.width = 10;
+    h.state.height = 10;
+
+    const rectElement = API.createElement({
+      width: 100,
+      height: 100,
+      x: -100,
+      y: -100,
+    });
+
+    act(() => {
+      // a short duration so the animation completes within a few frames
+      h.app.scrollToContent(rectElement, { animate: true, duration: 10 });
+    });
+
+    await waitForAnimationToStop();
+
+    // the animation must remove itself from the controller rather than keep
+    // ticking forever after reaching the target
+    expect(AnimationController.running(SCROLL_TO_CONTENT_ANIMATION_KEY)).toBe(
+      false,
+    );
+
+    // it should have settled on the target viewport (moved off the origin)
+    const settledScrollX = h.state.scrollX;
+    const settledScrollY = h.state.scrollY;
+    expect(settledScrollX).not.toBe(0);
+    expect(settledScrollY).not.toBe(0);
+    expect(h.state.shouldCacheIgnoreZoom).toBe(false);
+
+    // further frames must not move the viewport (no perpetual re-rendering)
+    await waitForAnimationProgress();
+    expect(h.state.scrollX).toBe(settledScrollX);
+    expect(h.state.scrollY).toBe(settledScrollY);
+  });
 });