prevent multiple legacy viewport conversions

Author: marcelduin

src/ts/utils/view.ts

@@ -5,6 +5,8 @@
 
 import type { Models } from '../../types/models';
 
+const fromLegacyDone:Set<Models.Camera.ViewRect | Models.Camera.View> = new Set();
+
 /**
  * View utility object for converting between view formats.
  * @internal
@@ -13,12 +15,15 @@ export const View = {
 	/** Casts a legacy view array ([x0, y0, x1, y1]) to [x0, y0, width, height]. */
 	fromLegacy: (v?: Models.Camera.ViewRect | Models.Camera.View): Models.Camera.View | undefined => {
 		if (!v) return undefined;
-		return [
+		if(fromLegacyDone.has(v)) return v;
+		const result = [
 			v[0],
 			v[1],
 			v[2] - v[0],
 			v[3] - v[1]
 		];
+		fromLegacyDone.add(result);
+		return result;
 	},
 
 	/** Converts a view to center-based JSON format. */