fix: linear elements drifting away after multiple flips

src/actions/actionFlip.ts

@@ -7,7 +7,13 @@ import { AppState, PointerDownState } from "../types";
 import { updateBoundElements } from "../element/binding";
 import { arrayToMap } from "../utils";
 import { KEYS } from "../keys";
-import { getCommonBoundingBox } from "../element/bounds";
+import {
+  getCommonBoundingBox,
+  getElementPointsCoords,
+} from "../element/bounds";
+import { isLinearElement } from "../element/typeChecks";
+import { type ExcalidrawLinearElement } from "../element/types";
+import { mutateElement } from "../element/mutateElement";
 
 const enableActionFlipHorizontal = (
   elements: readonly ExcalidrawElement[],
@@ -86,6 +92,15 @@ const flipElements = (
 ): ExcalidrawElement[] => {
   const { minX, minY, maxX, maxY } = getCommonBoundingBox(elements);
 
+  const linearElements = elements
+    .filter((element): element is ExcalidrawLinearElement =>
+      isLinearElement(element),
+    )
+    .map((element) => {
+      const origCoords = getElementPointsCoords(element, element.points);
+      return [element, origCoords] as const;
+    });
+
   resizeMultipleElements(
     { originalElements: arrayToMap(elements) } as PointerDownState,
     elements,
@@ -95,6 +110,19 @@ const flipElements = (
     flipDirection === "horizontal" ? minY : maxY,
   );
 
+  linearElements.forEach(([element, origCoords]) => {
+    const latestCoords = getElementPointsCoords(element, element.points);
+    const coordsDiffX =
+      origCoords[0] - latestCoords[0] + origCoords[2] - latestCoords[2];
+    const coordsDiffY =
+      origCoords[1] - latestCoords[1] + origCoords[3] - latestCoords[3];
+
+    mutateElement(element, {
+      x: element.x + coordsDiffX * 0.5,
+      y: element.y + coordsDiffY * 0.5,
+    });
+  });
+
   elements.forEach((element) => updateBoundElements(element));
 
   return elements;