effects/overview: Allow blurring desktop background

This puts more emphasis on windows and less on desktop background.

src/effects/overview/kcm/overvieweffectkcm.ui

@@ -37,26 +37,33 @@
      </item>
     </widget>
    </item>
-   <item row="1" column="0" colspan="2">
-    <widget class="KShortcutsEditor" name="shortcutsEditor" native="true">
+   <item row="2" column="0" colspan="2">
+    <widget class="KShortcutsEditor" name="shortcutsEditor">
      <property name="sizePolicy">
       <sizepolicy hsizetype="Preferred" vsizetype="Preferred">
        <horstretch>0</horstretch>
        <verstretch>0</verstretch>
       </sizepolicy>
      </property>
-     <property name="actionTypes">
-      <enum>KShortcutsEditor::GlobalAction</enum>
+    </widget>
+   </item>
+   <item row="1" column="0">
+    <widget class="QLabel" name="label_BlurBackground">
+     <property name="text">
+      <string>Blur background:</string>
      </property>
     </widget>
-    </item>
+   </item>
+   <item row="1" column="1">
+    <widget class="QCheckBox" name="kcfg_BlurBackground"/>
+   </item>
   </layout>
  </widget>
  <customwidgets>
   <customwidget>
    <class>KShortcutsEditor</class>
    <extends>QWidget</extends>
-   <header location="global">KShortcutsEditor</header>
+   <header>kshortcutseditor.h</header>
    <container>1</container>
   </customwidget>
  </customwidgets>

src/effects/overview/overviewconfig.kcfg

@@ -14,6 +14,10 @@
             <default>1</default>
         </entry>
 
+        <entry name="BlurBackground" type="Bool">
+            <default>true</default>
+        </entry>
+
         <entry name="BorderActivate" type="IntList" />
         <entry name="TouchBorderActivate" type="IntList" />
     </group>

src/effects/overview/overvieweffect.cpp

@@ -106,6 +106,7 @@ void OverviewEffect::reconfigure(ReconfigureFlags)
     OverviewConfig::self()->read();
     setLayout(ExpoLayout::LayoutMode(OverviewConfig::layoutMode()));
     setAnimationDuration(animationTime(200));
+    setBlurBackground(OverviewConfig::blurBackground());
 
     for (const ElectricBorder &border : qAsConst(m_borderActivate)) {
         effects->unreserveElectricBorder(border, this);
@@ -157,6 +158,19 @@ void OverviewEffect::setLayout(ExpoLayout::LayoutMode layout)
     }
 }
 
+bool OverviewEffect::blurBackground() const
+{
+    return m_blurBackground;
+}
+
+void OverviewEffect::setBlurBackground(bool blur)
+{
+    if (m_blurBackground != blur) {
+        m_blurBackground = blur;
+        Q_EMIT blurBackgroundChanged();
+    }
+}
+
 void OverviewEffect::paintScreen(int mask, const QRegion &region, ScreenPaintData &data)
 {
     Q_UNUSED(mask)

src/effects/overview/overvieweffect.h

@@ -40,6 +40,7 @@ class OverviewEffect : public Effect
     Q_OBJECT
     Q_PROPERTY(int animationDuration READ animationDuration NOTIFY animationDurationChanged)
     Q_PROPERTY(ExpoLayout::LayoutMode layout READ layout NOTIFY layoutChanged)
+    Q_PROPERTY(bool blurBackground READ blurBackground NOTIFY blurBackgroundChanged)
 
 public:
     OverviewEffect();
@@ -51,6 +52,9 @@ public:
     int animationDuration() const;
     void setAnimationDuration(int duration);
 
+    bool blurBackground() const;
+    void setBlurBackground(bool blur);
+
     void paintScreen(int mask, const QRegion &region, ScreenPaintData &data) override;
     void postPaintScreen() override;
     bool isActive() const override;
@@ -66,6 +70,7 @@ public:
 Q_SIGNALS:
     void animationDurationChanged();
     void layoutChanged();
+    void blurBackgroundChanged();
 
 public Q_SLOTS:
     void activate();
@@ -88,6 +93,7 @@ private:
     QList<QKeySequence> m_toggleShortcut;
     QList<ElectricBorder> m_borderActivate;
     QList<ElectricBorder> m_touchBorderActivate;
+    bool m_blurBackground = false;
     bool m_activated = false;
     int m_animationDuration = 200;
     ExpoLayout::LayoutMode m_layout = ExpoLayout::LayoutNatural;

src/effects/overview/qml/ScreenView.qml

@@ -5,6 +5,7 @@
 */
 
 import QtQuick 2.12
+import QtGraphicalEffects 1.12
 import org.kde.kwin 3.0 as KWinComponents
 import org.kde.kwin.private.overview 1.0
 import org.kde.plasma.components 3.0 as PC3
@@ -42,6 +43,15 @@ FocusScope {
             y: model.client.y - targetScreen.geometry.y
             width: model.client.width
             height: model.client.height
+
+            layer.enabled: effect.blurBackground
+            layer.effect: FastBlur {
+                radius: container.organized ? 64 : 0
+
+                Behavior on radius {
+                    NumberAnimation { duration: effect.animationDuration; easing.type: Easing.OutCubic }
+                }
+            }
         }
     }