external displays: mirror/extend switch

Add a mirror/extend built-in display switch. Make minor changes to
DisplayTopology.kt for consistency and correctness.

Kotlin requires the two preference key names are different since they
are in the same namespace, so fix the name in the existing
DisplayTopology.kt module.

Make DisplayTopologyPreference responsible, rather than the caller, for
setting its persistence property, since a wrong value may cause unusual
behavior.

The setOrder calls are necessary to prevent the new switch from
appearing below the Built-in display category when a display is
hot-plugged in after showing the UI. We set them on all top-level
preferences (not just the two we are fixing) for consistency.

Flag: com.android.settings.flags.display_topology_pane_in_display_list
Test: atest ExternalDisplayPreferenceFragmentTest.java
Bug: b/352648432
Bug: b/366056921
Change-Id: Ib0072dd75066758903cc48c2d1e7142e1d921f67

res/values/strings.xml

@@ -2120,6 +2120,8 @@
     <string name="external_display_more_options_title">More options</string>
     <!-- External Display settings. -->
     <string name="external_display_topology_hint">Hold and drag to rearrange displays.</string>
+    <!-- External Display settings. -->
+    <string name="external_display_mirroring_title">Mirror built-in display</string>
 
     <!-- Wifi Display settings. The title of the screen. [CHAR LIMIT=40] -->
     <string name="wifi_display_settings_title">Cast</string>

src/com/android/settings/connecteddevice/display/DisplayTopology.kt

@@ -157,7 +157,7 @@ class TopologyScale(
     }
 }
 
-const val PREFERENCE_KEY = "display_topology_preference"
+const val TOPOLOGY_PREFERENCE_KEY = "display_topology_preference"
 
 /** Padding in pane coordinate pixels on each side of a display block. */
 const val BLOCK_PADDING = 2f
@@ -220,7 +220,8 @@ class DisplayTopologyPreference(context : Context)
         // Prevent highlight when hovering with mouse.
         isSelectable = false
 
-        key = PREFERENCE_KEY
+        key = TOPOLOGY_PREFERENCE_KEY
+        isPersistent = false
 
         injector = Injector(context)
     }

src/com/android/settings/connecteddevice/display/ExternalDisplayPreferenceFragment.java

@@ -102,6 +102,8 @@ public class ExternalDisplayPreferenceFragment extends SettingsPreferenceFragmen
     @Nullable
     private Preference mDisplayTopologyPreference;
     @Nullable
+    private Preference mMirrorPreference;
+    @Nullable
     private PreferenceCategory mDisplaysPreference;
     @Nullable
     private PreferenceCategory mBuiltinDisplayPreference;
@@ -292,6 +294,7 @@ public class ExternalDisplayPreferenceFragment extends SettingsPreferenceFragmen
         if (mDisplaysPreference == null) {
             mDisplaysPreference = new PreferenceCategory(context);
             mDisplaysPreference.setPersistent(false);
+            mDisplaysPreference.setOrder(40);
         }
         return mDisplaysPreference;
     }
@@ -301,6 +304,7 @@ public class ExternalDisplayPreferenceFragment extends SettingsPreferenceFragmen
         if (mBuiltinDisplayPreference == null) {
             mBuiltinDisplayPreference = new PreferenceCategory(context);
             mBuiltinDisplayPreference.setPersistent(false);
+            mBuiltinDisplayPreference.setOrder(30);
         }
         return mBuiltinDisplayPreference;
     }
@@ -308,11 +312,19 @@ public class ExternalDisplayPreferenceFragment extends SettingsPreferenceFragmen
     @NonNull Preference getDisplayTopologyPreference(@NonNull Context context) {
         if (mDisplayTopologyPreference == null) {
             mDisplayTopologyPreference = new DisplayTopologyPreference(context);
-            mDisplayTopologyPreference.setPersistent(false);
+            mDisplayTopologyPreference.setOrder(10);
         }
         return mDisplayTopologyPreference;
     }
 
+    @NonNull Preference getMirrorPreference(@NonNull Context context) {
+        if (mMirrorPreference == null) {
+            mMirrorPreference = new MirrorPreference(context);
+            mMirrorPreference.setOrder(20);
+        }
+        return mMirrorPreference;
+    }
+
     private void restoreState(@Nullable Bundle savedInstanceState) {
         if (savedInstanceState == null) {
             return;
@@ -399,6 +411,9 @@ public class ExternalDisplayPreferenceFragment extends SettingsPreferenceFragmen
             @NonNull PreferenceScreen screen, @NonNull Context context) {
         if (mInjector != null && mInjector.getFlags().displayTopologyPaneInDisplayList()) {
             screen.addPreference(getDisplayTopologyPreference(context));
+            if (!displaysToShow.isEmpty()) {
+                screen.addPreference(getMirrorPreference(context));
+            }
 
             // If topology is shown, we also show a preference for the built-in display for
             // consistency with the topology.

src/com/android/settings/connecteddevice/display/Mirroring.kt

@@ -0,0 +1,51 @@
+/*
+ * Copyright (C) 2025 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.settings.connecteddevice.display
+
+import android.content.Context
+import android.provider.Settings
+
+import androidx.preference.SwitchPreferenceCompat
+
+import com.android.settings.R
+
+const val MIRROR_PREFERENCE_KEY = "mirror_builtin_display"
+
+/**
+ * A switch preference which is backed by the MIRROR_BUILT_IN_DISPLAY global setting.
+ */
+class MirrorPreference(context: Context): SwitchPreferenceCompat(context) {
+    init {
+        setTitle(R.string.external_display_mirroring_title)
+
+        key = MIRROR_PREFERENCE_KEY
+        isPersistent = false
+    }
+
+    override fun onAttached() {
+        super.onAttached()
+        setChecked(0 != Settings.Global.getInt(
+                context.contentResolver, Settings.Secure.MIRROR_BUILT_IN_DISPLAY, 0))
+    }
+
+    override fun onClick() {
+        super.onClick()
+        Settings.Global.putInt(
+                context.contentResolver, Settings.Secure.MIRROR_BUILT_IN_DISPLAY,
+                if (isChecked()) 1 else 0)
+    }
+}

tests/unit/src/com/android/settings/connecteddevice/display/ExternalDisplayPreferenceFragmentTest.java

@@ -105,7 +105,7 @@ public class ExternalDisplayPreferenceFragmentTest extends ExternalDisplayTestBa
         fragment.onSaveInstanceStateCallback(outState);
         assertThat(outState.getBoolean(PREVIOUSLY_SHOWN_LIST_KEY)).isTrue();
 
-        pref = mPreferenceScreen.findPreference(DisplayTopologyKt.PREFERENCE_KEY);
+        pref = mPreferenceScreen.findPreference(DisplayTopologyKt.TOPOLOGY_PREFERENCE_KEY);
         assertThat(pref).isNull();
 
         pref = mPreferenceScreen.findPreference(
@@ -122,7 +122,9 @@ public class ExternalDisplayPreferenceFragmentTest extends ExternalDisplayTestBa
         doReturn(new Display[] {mDisplays[1]}).when(mMockedInjector).getAllDisplays();
         mHandler.flush();
 
-        var pref = mPreferenceScreen.findPreference(DisplayTopologyKt.PREFERENCE_KEY);
+        var pref = mPreferenceScreen.findPreference(DisplayTopologyKt.TOPOLOGY_PREFERENCE_KEY);
+        assertThat(pref).isNotNull();
+        pref = mPreferenceScreen.findPreference(MirroringKt.MIRROR_PREFERENCE_KEY);
         assertThat(pref).isNotNull();
 
         PreferenceCategory listPref =
@@ -145,8 +147,10 @@ public class ExternalDisplayPreferenceFragmentTest extends ExternalDisplayTestBa
         doReturn(new Display[0]).when(mMockedInjector).getAllDisplays();
         mHandler.flush();
 
-        var pref = mPreferenceScreen.findPreference(DisplayTopologyKt.PREFERENCE_KEY);
+        var pref = mPreferenceScreen.findPreference(DisplayTopologyKt.TOPOLOGY_PREFERENCE_KEY);
         assertThat(pref).isNotNull();
+        pref = mPreferenceScreen.findPreference(MirroringKt.MIRROR_PREFERENCE_KEY);
+        assertThat(pref).isNull();
 
         PreferenceCategory listPref =
                 mPreferenceScreen.findPreference(DISPLAYS_LIST_PREFERENCE_KEY);