add opacity settings for obscured windows

package/contents/ui/config.ui

@@ -183,6 +183,27 @@
                                     </property>
                                 </widget>
                             </item>
+
+                            <item row="8" column="0">
+                                <widget class="QLabel" name="label_offScreenOpacity">
+                                    <property name="text">
+                                        <string>Obscured window opacity:</string>
+                                    </property>
+                                </widget>
+                            </item>
+                            <item row="8" column="1">
+                                <widget class="QSpinBox" name="kcfg_offScreenOpacity">
+                                    <property name="suffix">
+                                        <string> %</string>
+                                    </property>
+                                    <property name="maximum">
+                                        <number>100</number>
+                                    </property>
+                                    <property name="value">
+                                        <number>0</number>
+                                    </property>
+                                </widget>
+                            </item>
                         </layout>
                     </widget>
 

src/config/config.ts

@@ -7,6 +7,7 @@ type Config = {
     gapsInnerVertical: number,
     overscroll: number,
     manualScrollStep: number,
+    offScreenOpacity: number,
     untileOnDrag: boolean,
     stackColumnsByDefault: boolean,
     resizeNeighborColumn: boolean,

src/config/definition.ts

@@ -92,6 +92,11 @@ const configDef = [
         "type": "UInt",
         "default": 200
     },
+    {
+        "name": "offScreenOpacity",
+        "type": "UInt",
+        "default": 100
+    },
     {
         "name": "untileOnDrag",
         "type": "Bool",

src/extern/kwin.d.ts

@@ -47,6 +47,7 @@ interface KwinClient {
     readonly dock: boolean;
     readonly normalWindow: boolean;
     readonly managed: boolean;
+    opacity: number;
 
     // Read-write Properties
     fullScreen: boolean;

src/layout/Column.ts

@@ -181,6 +181,13 @@ class Column {
     }
 
     public arrange(x: number) {
+        if (this.grid.config.offScreenOpacity < 1.0) {
+            const opacity = this.isVisible(this.grid.desktop.getCurrentVisibleRange(), true) ? 100 : this.grid.config.offScreenOpacity;
+            for (const window of this.windows.iterator()) {
+                window.client.kwinClient.opacity = opacity;
+            }
+        }
+
         if (this.stacked && this.windows.length() >= 2 && this.canStack()) {
             this.arrangeStacked(x);
             return;

src/layout/LayoutConfig.ts

@@ -1,6 +1,7 @@
 type LayoutConfig = {
     gapsInnerHorizontal: number,
     gapsInnerVertical: number,
+    offScreenOpacity: number,
     stackColumnsByDefault: boolean,
     resizeNeighborColumn: boolean,
     reMaximize: boolean,

src/world/World.ts

@@ -24,6 +24,7 @@ class World {
         const layoutConfig = {
             gapsInnerHorizontal: config.gapsInnerHorizontal,
             gapsInnerVertical: config.gapsInnerVertical,
+            offScreenOpacity: config.offScreenOpacity / 100.0,
             stackColumnsByDefault: config.stackColumnsByDefault,
             resizeNeighborColumn: config.resizeNeighborColumn,
             reMaximize: config.reMaximize,