Column: prevent stacking columns with unshadeable windows

src/extern/kwin.d.ts

@@ -34,6 +34,7 @@ type Tile = any;
 
 interface KwinClient {
     // Read-only Properties
+    readonly shadeable: boolean;
     readonly caption: string;
     readonly minSize: QSize;
     readonly transient: boolean;

src/layout/Column.ts

@@ -181,7 +181,7 @@ class Column {
     }
 
     public arrange(x: number) {
-        if (this.stacked && this.windows.length() >= 2) {
+        if (this.stacked && this.windows.length() >= 2 && this.canStack()) {
             this.arrangeStacked(x);
             return;
         }
@@ -228,6 +228,15 @@ class Column {
         this.grid.desktop.onLayoutChanged();
     }
 
+    private canStack() {
+        for (const window of this.windows.iterator()) {
+            if (!window.client.kwinClient.shadeable) {
+                return false;
+            }
+        }
+        return true;
+    }
+
     public isVisible(scrollPos: Desktop.ScrollPos, fullyVisible: boolean) {
         if (fullyVisible) {
             return this.getLeft() >= scrollPos.getLeft() &&