feat: Unify scroll constraint

Signed-off-by: Mark Tolmacs <mark@lazycat.hu>

excalidraw-app/components/AppFooter.tsx

@@ -26,7 +26,8 @@ const ScrollConstraintsDebugFooter = ({
 
   const setLock = useCallback(
     (nextLock: ScrollConstraints) => {
-      excalidrawAPI?.setScrollConstraints(nextLock);
+      // pass an empty target so the constraints are applied without scrolling
+      excalidrawAPI?.scrollToContent([], { scrollConstraints: nextLock });
       setActiveLock(nextLock);
     },
     [excalidrawAPI],
@@ -38,7 +39,7 @@ const ScrollConstraintsDebugFooter = ({
     }
 
     if (activeLock) {
-      excalidrawAPI.setScrollConstraints(null);
+      excalidrawAPI.scrollToContent([], { scrollConstraints: null });
       setActiveLock(null);
       return;
     }

packages/excalidraw/components/App.tsx

@@ -501,7 +501,6 @@ import type {
   GenerateDiagramToCode,
   NullableGridSize,
   Offsets,
-  ScrollConstraints,
 } from "../types";
 import type { RoughCanvas } from "roughjs/bin/canvas";
 import type { Action, ActionResult } from "../actions/types";
@@ -768,7 +767,6 @@ class App extends React.Component<AppProps, AppState> {
         clear: this.resetHistory,
       },
       scrollToContent: this.scrollToContent,
-      setScrollConstraints: this.setScrollConstraints,
       getSceneElements: this.getSceneElements,
       getAppState: () => this.state,
       getFiles: () => this.files,
@@ -4370,6 +4368,16 @@ class App extends React.Component<AppProps, AppState> {
       elements = this.scene.getNonDeletedElements();
     }
 
+    const scrollConstraints = opts?.scrollConstraints ?? null;
+    if (scrollConstraints || this.state.scrollConstraints) {
+      flushSync(() => {
+        this.setState((prevState) => ({
+          scrollConstraints,
+          ...constrainScrollState({ ...prevState, scrollConstraints }),
+        }));
+      });
+    }
+
     if (!elements.length) {
       if (typeof target === "string" && isElementLink(target)) {
         this.setState({
@@ -4384,8 +4392,6 @@ class App extends React.Component<AppProps, AppState> {
       return;
     }
 
-    this.setScrollConstraints(null);
-
     // Navigating to an element by id or element-link defaults to zooming the
     // element into view, animated — matching the historical element-link
     // behavior — unless the caller opts out.
@@ -4454,26 +4460,6 @@ class App extends React.Component<AppProps, AppState> {
     SCROLL_CONSTRAINTS_SNAP_BACK_DELAY,
   );
 
-  /**
-   * Constrains pan & zoom to a scene-coordinate box, so the viewport can't be
-   * scrolled or zoomed out past it. Pass `null` to remove the constraint. When
-   * the box is smaller than the viewport, zoom is increased best-effort to fit.
-   *
-   * Optional `minZoom`/`maxZoom` take precedence over the box: `minZoom` lets
-   * the viewport zoom out past the fit zoom, while `maxZoom` caps zoom-in below
-   * the global limit.
-   */
-  setScrollConstraints = (scrollConstraints: ScrollConstraints | null) => {
-    // apply the constraint and clamp the viewport in a single, synchronously
-    // flushed update so the new scroll/zoom is reflected immediately
-    flushSync(() => {
-      this.setState((prevState) => ({
-        scrollConstraints,
-        ...constrainScrollState({ ...prevState, scrollConstraints }),
-      }));
-    });
-  };
-
   setToast = (toast: AppState["toast"]) => {
     this.setState({ toast });
   };

packages/excalidraw/scroll.ts

@@ -41,6 +41,7 @@ export type ScrollToContentOptions = (
   minZoom?: number;
   maxZoom?: number;
   canvasOffsets?: Offsets;
+  scrollConstraints?: ScrollConstraints | null;
 };
 
 type Viewport = Pick<AppState, "scrollX" | "scrollY" | "zoom">;
@@ -263,6 +264,8 @@ const getTargetViewport = (
   targetElements: readonly ExcalidrawElement[],
   opts?: ScrollToContentOptions,
 ): Viewport => {
+  let viewport: Viewport;
+
   if (opts?.fitToContent || opts?.fitToViewport) {
     const { appState } = zoomToFit({
       canvasOffsets: opts.canvasOffsets,
@@ -274,16 +277,19 @@ const getTargetViewport = (
       maxZoom: opts.maxZoom,
     });
 
-    return {
+    viewport = {
       scrollX: appState.scrollX,
       scrollY: appState.scrollY,
       zoom: appState.zoom,
     };
+  } else {
+    // keep the current zoom, only recenter the viewport on the target
+    const { scrollX, scrollY } = calculateScrollCenter(targetElements, state);
+    viewport = { scrollX, scrollY, zoom: state.zoom };
   }
-  // keep the current zoom, only recenter the viewport on the target
-  const { scrollX, scrollY } = calculateScrollCenter(targetElements, state);
 
-  return { scrollX, scrollY, zoom: state.zoom };
+  // keep the target inside any active scroll constraints (no-op otherwise)
+  return constrainScrollState({ ...state, ...viewport });
 };
 
 /**

packages/excalidraw/tests/scrollConstraints.test.tsx

@@ -19,6 +19,7 @@ import {
 } from "../scroll";
 import { AnimationController } from "../renderer/animation";
 
+import { API } from "./helpers/api";
 import { Keyboard } from "./helpers/ui";
 import {
   mockBoundingClientRect,
@@ -151,7 +152,7 @@ describe("constrainScrollState (pure)", () => {
   });
 });
 
-describe("setScrollConstraints (integration)", () => {
+describe("scrollToContent scrollConstraints (integration)", () => {
   beforeEach(() => {
     mockBoundingClientRect();
   });
@@ -166,7 +167,9 @@ describe("setScrollConstraints (integration)", () => {
 
     // start well outside the future box
     React.act(() => {
-      h.app.setScrollConstraints({ x: 0, y: 0, width: 1000, height: 1000 });
+      h.app.scrollToContent([], {
+        scrollConstraints: { x: 0, y: 0, width: 1000, height: 1000 },
+      });
     });
 
     // viewport must now be within [-800, 0] x [-900, 0]
@@ -182,7 +185,9 @@ describe("setScrollConstraints (integration)", () => {
     await waitFor(() => expect(h.state.width).toBe(200));
 
     React.act(() => {
-      h.app.setScrollConstraints({ x: 0, y: 0, width: 300, height: 200 });
+      h.app.scrollToContent([], {
+        scrollConstraints: { x: 0, y: 0, width: 300, height: 200 },
+      });
     });
 
     // hammer page-down (pans down) far past the box; scroll must stay clamped
@@ -193,13 +198,40 @@ describe("setScrollConstraints (integration)", () => {
 
     // clearing constraints lets it scroll freely again
     React.act(() => {
-      h.app.setScrollConstraints(null);
+      h.app.scrollToContent([], { scrollConstraints: null });
     });
     const before = h.state.scrollY;
     Keyboard.keyPress(KEYS.PAGE_DOWN);
     expect(h.state.scrollY).toBeLessThan(before);
   });
 
+  it("clamps the scroll target into the box when scrolling to content", async () => {
+    await render(<Excalidraw />);
+    await waitFor(() => expect(h.state.width).toBe(200));
+
+    // an element well outside the future constraint box
+    const rect = API.createElement({
+      type: "rectangle",
+      x: 2000,
+      y: 2000,
+      width: 100,
+      height: 100,
+    });
+    API.setElements([rect]);
+
+    React.act(() => {
+      h.app.scrollToContent(rect, {
+        scrollConstraints: { x: 0, y: 0, width: 1000, height: 1000 },
+        animate: false,
+      });
+    });
+
+    // recentering on the element would scroll way past the box; it must be
+    // clamped to the far edges instead (scrollX -800, scrollY -900 at zoom 1)
+    expect(h.state.scrollX).toBeCloseTo(-800);
+    expect(h.state.scrollY).toBeCloseTo(-900);
+  });
+
   it("disables reset-zoom and zoom-to-fit actions while constrained", async () => {
     await render(<Excalidraw />);
     await waitFor(() => expect(h.state.width).toBe(200));
@@ -208,7 +240,9 @@ describe("setScrollConstraints (integration)", () => {
     expect(h.app.actionManager.isActionEnabled(actionZoomToFit)).toBe(true);
 
     React.act(() => {
-      h.app.setScrollConstraints({ x: 0, y: 0, width: 500, height: 500 });
+      h.app.scrollToContent([], {
+        scrollConstraints: { x: 0, y: 0, width: 500, height: 500 },
+      });
     });
 
     expect(h.app.actionManager.isActionEnabled(actionResetZoom)).toBe(false);
@@ -468,12 +502,14 @@ describe("rubberband tolerance (integration)", () => {
     await waitFor(() => expect(h.state.width).toBe(200));
 
     React.act(() => {
-      h.app.setScrollConstraints({
-        x: 0,
-        y: 0,
-        width: 1000,
-        height: 1000,
-        tolerance: 25,
+      h.app.scrollToContent([], {
+        scrollConstraints: {
+          x: 0,
+          y: 0,
+          width: 1000,
+          height: 1000,
+          tolerance: 25,
+        },
       });
     });
 

packages/excalidraw/types.ts

@@ -411,7 +411,7 @@ export interface AppState {
   scrollX: number;
   scrollY: number;
   /** when set, pan & zoom are constrained so the viewport stays within this
-   * scene-coordinate box (see `setScrollConstraints`) */
+   * scene-coordinate box (see `scrollToContent`'s `scrollConstraints` option) */
   scrollConstraints: ScrollConstraints | null;
   cursorButton: "up" | "down";
   scrolledOutside: boolean;
@@ -1004,7 +1004,6 @@ export interface ExcalidrawImperativeAPI {
   getFiles: () => InstanceType<typeof App>["files"];
   getName: InstanceType<typeof App>["getName"];
   scrollToContent: InstanceType<typeof App>["scrollToContent"];
-  setScrollConstraints: InstanceType<typeof App>["setScrollConstraints"];
   registerAction: (action: Action) => void;
   refresh: InstanceType<typeof App>["refresh"];
   setToast: InstanceType<typeof App>["setToast"];