Add a flag to determin whether to support legacy split

Bug: 187041611
Test: launch with adjacent flag won't trigger stage split
Change-Id: Iefaad20636dda88caa6988802d1b7640b5077e4e

core/res/res/values/config.xml

@@ -3552,6 +3552,9 @@
     -->
     <integer name="config_largeScreenSmallestScreenWidthDp">600</integer>
 
+    <!-- True if the device is using leagacy split. -->
+    <bool name="config_useLegacySplit">true</bool>
+
     <!-- True if the device supports running activities on secondary displays. -->
     <bool name="config_supportsMultiDisplay">true</bool>
 

core/res/res/values/symbols.xml

@@ -396,6 +396,7 @@
   <java-symbol type="integer" name="config_respectsActivityMinWidthHeightMultiWindow" />
   <java-symbol type="dimen" name="config_minPercentageMultiWindowSupportWidth" />
   <java-symbol type="integer" name="config_largeScreenSmallestScreenWidthDp" />
+  <java-symbol type="bool" name="config_useLegacySplit" />
   <java-symbol type="bool" name="config_noHomeScreen" />
   <java-symbol type="bool" name="config_supportsSystemDecorsOnSecondaryDisplays" />
   <java-symbol type="bool" name="config_supportsInsecureLockScreen" />

libs/WindowManager/Shell/src/com/android/wm/shell/splitscreen/StageCoordinator.java

@@ -55,6 +55,7 @@ import android.window.TransitionRequestInfo;
 import android.window.WindowContainerTransaction;
 
 
+import com.android.internal.R;
 import com.android.internal.annotations.VisibleForTesting;
 import com.android.internal.protolog.common.ProtoLog;
 import com.android.wm.shell.RootTaskDisplayAreaOrganizer;
@@ -110,6 +111,11 @@ class StageCoordinator implements SplitLayout.LayoutChangeListener,
     private final SplitScreenTransitions mSplitTransitions;
     private boolean mExitSplitScreenOnHide = true;
 
+    // TODO(b/187041611): remove this flag after totally deprecated legacy split
+    /** Whether the device is supporting legacy split or not. */
+    private boolean mUseLegacySplit;
+
+
     @SplitScreen.StageType int mDismissTop = NO_DISMISS;
     private final Runnable mOnTransitionAnimationComplete = () -> {
         // If still playing, let it finish.
@@ -334,10 +340,17 @@ class StageCoordinator implements SplitLayout.LayoutChangeListener,
 
     private void onStageRootTaskAppeared(StageListenerImpl stageListener) {
         if (mMainStageListener.mHasRootTask && mSideStageListener.mHasRootTask) {
+            mUseLegacySplit = mContext.getResources().getBoolean(R.bool.config_useLegacySplit);
             final WindowContainerTransaction wct = new WindowContainerTransaction();
             // Make the stages adjacent to each other so they occlude what's behind them.
             wct.setAdjacentRoots(mMainStage.mRootTaskInfo.token, mSideStage.mRootTaskInfo.token);
-            wct.setLaunchAdjacentFlagRoot(mSideStage.mRootTaskInfo.token);
+
+            // Only sets side stage as launch-adjacent-flag-root when the device is not using legacy
+            // split to prevent new split behavior confusing users.
+            if (!mUseLegacySplit) {
+                wct.setLaunchAdjacentFlagRoot(mSideStage.mRootTaskInfo.token);
+            }
+
             mTaskOrganizer.applyTransaction(wct);
         }
     }
@@ -347,7 +360,11 @@ class StageCoordinator implements SplitLayout.LayoutChangeListener,
             final WindowContainerTransaction wct = new WindowContainerTransaction();
             // Deactivate the main stage if it no longer has a root task.
             mMainStage.deactivate(wct);
-            wct.clearLaunchAdjacentFlagRoot(mSideStage.mRootTaskInfo.token);
+
+            if (!mUseLegacySplit) {
+                wct.clearLaunchAdjacentFlagRoot(mSideStage.mRootTaskInfo.token);
+            }
+
             mTaskOrganizer.applyTransaction(wct);
         }
     }