diff --git a/src/engine/window.ts b/src/engine/window.ts
index ca5c851..7a6da00 100644
--- a/src/engine/window.ts
+++ b/src/engine/window.ts
@@ -19,23 +19,26 @@
 // DEALINGS IN THE SOFTWARE.
 
 class WindowResizeDelta {
-    public readonly diff: Rect;
-    public readonly east: number;
-    public readonly west: number;
-    public readonly south: number;
-    public readonly north: number;
+    public static fromWindow(window: Window): WindowResizeDelta {
+        const diff = window.actualGeometry.subtract(window.geometry);
+        return new WindowResizeDelta(
+            diff.width + diff.x,
+            -diff.x,
+            diff.height + diff.y,
+            -diff.y,
+        );
+    }
 
-    public constructor(window: Window) {
-        this.diff = window.actualGeometry.subtract(window.geometry);
-        this.east = this.diff.width + this.diff.x;
-        this.west = -this.diff.x;
-        this.south = this.diff.height + this.diff.y;
-        this.north = -this.diff.y;
+    constructor(
+        public readonly east: number,
+        public readonly west: number,
+        public readonly south: number,
+        public readonly north: number,
+    ) {
     }
 
     public toString(): string {
         return "WindowResizeDelta(" + [
-            "diff=" + this.diff,
             "east=" + this.east,
             "west=" + this.west,
             "north=" + this.north,
diff --git a/src/layouts/quarterlayout.ts b/src/layouts/quarterlayout.ts
index 69fc541..24b7a6a 100644
--- a/src/layouts/quarterlayout.ts
+++ b/src/layouts/quarterlayout.ts
@@ -43,7 +43,7 @@ class QuarterLayout implements ILayout {
         if (idx < 0)
             return;
 
-        const delta = new WindowResizeDelta(basis);
+        const delta = WindowResizeDelta.fromWindow(basis);
 
         /* vertical split */
         if ((idx === 0 || idx === 3) && delta.east !== 0)
diff --git a/src/layouts/tilelayout.ts b/src/layouts/tilelayout.ts
index 6fbff73..6d1984e 100644
--- a/src/layouts/tilelayout.ts
+++ b/src/layouts/tilelayout.ts
@@ -44,7 +44,7 @@ class TileLayout implements ILayout {
         if (idx < 0)
             return;
 
-        const delta = new WindowResizeDelta(basis);
+        const delta = WindowResizeDelta.fromWindow(basis);
         if (idx < this.numMaster) { /* master tiles */
             if (delta.east !== 0) {
                 const newMasterWidth = Math.floor(area.width * this.masterRatio) + delta.east;