feat: minZoom and maxZoom

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

packages/excalidraw/components/App.tsx

@@ -4458,6 +4458,10 @@ class App extends React.Component<AppProps, AppState> {
    * 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

packages/excalidraw/scroll.ts

@@ -94,6 +94,11 @@ const constrainScrollAxis = (
  * viewport may pan past the box edges (and zoom out below the fit zoom) until
  * each edge has crossed the box by up to `tolerance` pixels on screen,
  * independent of the current zoom. Pass `0` (default) for a hard clamp.
+ *
+ * An explicit `minZoom`/`maxZoom` on the constraints takes precedence over the
+ * zoom the box would otherwise enforce: `minZoom` replaces the fit zoom (so the
+ * viewport may zoom out past the box) and `maxZoom` replaces the global
+ * `MAX_ZOOM` cap.
  */
 export const constrainScrollState = (
   state: Pick<
@@ -110,14 +115,20 @@ export const constrainScrollState = (
 
   tolerance = Math.max(tolerance, 0);
 
-  // relax the min zoom so the user can briefly zoom out past the fit zoom,
-  // letting each viewport edge cross the box by up to `tolerance` screen px
-  const relaxedMinZoom = getMinZoomForConstraints(scrollConstraints, {
-    width: width - 2 * tolerance,
-    height: height - 2 * tolerance,
-  });
+  // zoom bounds: an explicit min/maxZoom on the constraints takes precedence
+  // over the box-enforced fit zoom (lower) and the global MAX_ZOOM (upper).
+  // Without a `minZoom`, relax the fit zoom by `tolerance` so the user can
+  // briefly zoom out past it (rubberbanding), letting each viewport edge cross
+  // the box by up to `tolerance` screen px.
+  const minZoom =
+    scrollConstraints.minZoom ??
+    getMinZoomForConstraints(scrollConstraints, {
+      width: width - 2 * tolerance,
+      height: height - 2 * tolerance,
+    });
+  const maxZoom = scrollConstraints.maxZoom ?? MAX_ZOOM;
   const zoomValue = getNormalizedZoom(
-    clamp(state.zoom.value, relaxedMinZoom, MAX_ZOOM),
+    clamp(state.zoom.value, minZoom, maxZoom),
   );
 
   // `tolerance` screen px expressed in scene coords at the current zoom

packages/excalidraw/tests/scrollConstraints.test.tsx

@@ -219,6 +219,51 @@ describe("setScrollConstraints (integration)", () => {
   });
 });
 
+describe("explicit minZoom / maxZoom (pure)", () => {
+  const box: ScrollConstraints = { x: 0, y: 0, width: 1000, height: 1000 };
+
+  it("lets minZoom override the box-enforced fit zoom (zoom out past the box)", () => {
+    // without minZoom the box forces a fit zoom of 0.2; minZoom 0.1 takes over
+    const { zoom } = constrainScrollState(
+      makeState({
+        zoom: { value: getNormalizedZoom(0.1) },
+        scrollConstraints: { ...box, minZoom: 0.1 },
+      }),
+    );
+    expect(zoom.value).toBeCloseTo(0.1);
+  });
+
+  it("still clamps zoom out at minZoom", () => {
+    const { zoom } = constrainScrollState(
+      makeState({
+        zoom: { value: getNormalizedZoom(0.1) },
+        scrollConstraints: { ...box, minZoom: 0.5 },
+      }),
+    );
+    expect(zoom.value).toBeCloseTo(0.5);
+  });
+
+  it("lets maxZoom cap zoom-in below the global MAX_ZOOM", () => {
+    const { zoom } = constrainScrollState(
+      makeState({
+        zoom: { value: getNormalizedZoom(MAX_ZOOM) },
+        scrollConstraints: { ...box, maxZoom: 3 },
+      }),
+    );
+    expect(zoom.value).toBeCloseTo(3);
+  });
+
+  it("leaves an in-range zoom untouched", () => {
+    const { zoom } = constrainScrollState(
+      makeState({
+        zoom: { value: getNormalizedZoom(1.5) },
+        scrollConstraints: { ...box, minZoom: 0.5, maxZoom: 3 },
+      }),
+    );
+    expect(zoom.value).toBeCloseTo(1.5);
+  });
+});
+
 describe("rubberband tolerance (pure)", () => {
   const box: ScrollConstraints = { x: 0, y: 0, width: 1000, height: 1000 };
 

packages/excalidraw/types.ts

@@ -279,7 +279,21 @@ export type ScrollConstraints = {
   y: number;
   width: number;
   height: number;
+  /**
+   * Pixel amount to allow to overscroll.
+   */
   tolerance?: number;
+  /**
+   * Lower zoom bound. When set, it takes precedence over the zoom the box would
+   * otherwise enforce (the fit zoom that keeps the box covering the viewport),
+   * letting the viewport zoom out past the box.
+   */
+  minZoom?: number;
+  /**
+   * Upper zoom bound. When set, it takes precedence over the global `MAX_ZOOM`,
+   * capping how far the viewport can zoom in.
+   */
+  maxZoom?: number;
 };
 
 export interface AppState {