1 files changed, 91 insertions, 0 deletions
diff --git a/packages/excalidraw/scene/scroll.ts b/packages/excalidraw/scene/scroll.ts
new file mode 100644
index 0000000..5d059e5
--- /dev/null
+++ b/packages/excalidraw/scene/scroll.ts
@@ -0,0 +1,91 @@
+import type { AppState, Offsets, PointerCoords, Zoom } from "../types";
+import type { ExcalidrawElement } from "../element/types";
+import {
+  getCommonBounds,
+  getClosestElementBounds,
+  getVisibleElements,
+} from "../element";
+
+import {
+  sceneCoordsToViewportCoords,
+  viewportCoordsToSceneCoords,
+} from "../utils";
+
+const isOutsideViewPort = (appState: AppState, cords: Array<number>) => {
+  const [x1, y1, x2, y2] = cords;
+  const { x: viewportX1, y: viewportY1 } = sceneCoordsToViewportCoords(
+    { sceneX: x1, sceneY: y1 },
+    appState,
+  );
+  const { x: viewportX2, y: viewportY2 } = sceneCoordsToViewportCoords(
+    { sceneX: x2, sceneY: y2 },
+    appState,
+  );
+  return (
+    viewportX2 - viewportX1 > appState.width ||
+    viewportY2 - viewportY1 > appState.height
+  );
+};
+
+export const centerScrollOn = ({
+  scenePoint,
+  viewportDimensions,
+  zoom,
+  offsets,
+}: {
+  scenePoint: PointerCoords;
+  viewportDimensions: { height: number; width: number };
+  zoom: Zoom;
+  offsets?: Offsets;
+}) => {
+  let scrollX =
+    (viewportDimensions.width - (offsets?.right ?? 0)) / 2 / zoom.value -
+    scenePoint.x;
+
+  scrollX += (offsets?.left ?? 0) / 2 / zoom.value;
+
+  let scrollY =
+    (viewportDimensions.height - (offsets?.bottom ?? 0)) / 2 / zoom.value -
+    scenePoint.y;
+
+  scrollY += (offsets?.top ?? 0) / 2 / zoom.value;
+
+  return {
+    scrollX,
+    scrollY,
+  };
+};
+
+export const calculateScrollCenter = (
+  elements: readonly ExcalidrawElement[],
+  appState: AppState,
+): { scrollX: number; scrollY: number } => {
+  elements = getVisibleElements(elements);
+
+  if (!elements.length) {
+    return {
+      scrollX: 0,
+      scrollY: 0,
+    };
+  }
+  let [x1, y1, x2, y2] = getCommonBounds(elements);
+
+  if (isOutsideViewPort(appState, [x1, y1, x2, y2])) {
+    [x1, y1, x2, y2] = getClosestElementBounds(
+      elements,
+      viewportCoordsToSceneCoords(
+        { clientX: appState.scrollX, clientY: appState.scrollY },
+        appState,
+      ),
+    );
+  }
+
+  const centerX = (x1 + x2) / 2;
+  const centerY = (y1 + y2) / 2;
+
+  return centerScrollOn({
+    scenePoint: { x: centerX, y: centerY },
+    viewportDimensions: { width: appState.width, height: appState.height },
+    zoom: appState.zoom,
+  });
+};