Expose mirror of wallpaper surface in WindowManagerGlobal.

Test: Manual
Bug: 188222480
Change-Id: I92302053a797de76aec3c2a25e5d895cfc85e6d5

core/java/android/view/IWindowManager.aidl

@@ -346,6 +346,14 @@ interface IWindowManager
      */
     Bitmap screenshotWallpaper();
 
+    /**
+     * Mirrors the wallpaper for the given display.
+     *
+     * @param displayId ID of the display for the wallpaper.
+     * @return A SurfaceControl for the parent of the mirrored wallpaper.
+     */
+    SurfaceControl mirrorWallpaperSurface(int displayId);
+
     /**
      * Registers a wallpaper visibility listener.
      * @return Current visibility.

core/java/android/view/WindowManagerGlobal.java

@@ -18,6 +18,7 @@ package android.view;
 
 import android.animation.ValueAnimator;
 import android.annotation.NonNull;
+import android.annotation.Nullable;
 import android.app.ActivityManager;
 import android.compat.annotation.UnsupportedAppUsage;
 import android.content.ComponentCallbacks2;
@@ -709,6 +710,16 @@ public final class WindowManagerGlobal {
             }
         }
     }
+
+    /** @hide */
+    @Nullable
+    public SurfaceControl mirrorWallpaperSurface(int displayId) {
+        try {
+            return getWindowManagerService().mirrorWallpaperSurface(displayId);
+        } catch (RemoteException e) {
+            throw e.rethrowFromSystemServer();
+        }
+    }
 }
 
 final class WindowLeaked extends AndroidRuntimeException {

services/core/java/com/android/server/wm/WallpaperController.java

@@ -801,6 +801,18 @@ class WallpaperController {
                 wallpaperBuffer.getHardwareBuffer(), wallpaperBuffer.getColorSpace());
     }
 
+    /**
+     * Mirrors the visible wallpaper if it's available.
+     *
+     * @return A SurfaceControl for the parent of the mirrored wallpaper.
+     */
+    SurfaceControl mirrorWallpaperSurface() {
+        final WindowState wallpaperWindowState = getTopVisibleWallpaper();
+        return wallpaperWindowState != null
+                ? SurfaceControl.mirrorSurface(wallpaperWindowState.getSurfaceControl())
+                : null;
+    }
+
     WindowState getTopVisibleWallpaper() {
         mTmpTopWallpaper = null;
 

services/core/java/com/android/server/wm/WindowManagerService.java

@@ -3791,6 +3791,14 @@ public class WindowManagerService extends IWindowManager.Stub
         }
     }
 
+    @Override
+    public SurfaceControl mirrorWallpaperSurface(int displayId) {
+        synchronized (mGlobalLock) {
+            final DisplayContent dc = mRoot.getDisplayContent(displayId);
+            return dc.mWallpaperController.mirrorWallpaperSurface();
+        }
+    }
+
     /**
      * Takes a snapshot of the screen.  In landscape mode this grabs the whole screen.
      * In portrait mode, it grabs the upper region of the screen based on the vertical dimension