Optimize handling of scrolled wallpapers

Swiping the home screen causes the WindowManagerService to do
a bunch of work to keep the wallpapers in sync. First, it lays out
and places all windows. Also, it notifies the SystemUI process that
the wallpaper position has changed.

The layout/place operation is too much work - we only need to set
the position values for the wallpaper, not relayout the whole system.

The notification mechanism must exist, but should be optional. Most
wallpapers don't care (especially static ImageWallpapers). So we'll
give them a new API (WallpaperService.Engine.setWantsOffsets()) to
allow wallpapers to opt out of this process and avoid the performance
overhead.

Change-Id: I66c38375438937f14f6f5550565b28eb204b1e06

1 files changed, 28 insertions, 1 deletions

diff --git a/core/java/android/service/wallpaper/WallpaperService.java b/core/java/android/service/wallpaper/WallpaperService.java
index ba94ab2..a9a628a 100644
--- a/core/java/android/service/wallpaper/WallpaperService.java
+++ b/core/java/android/service/wallpaper/WallpaperService.java
@@ -148,7 +148,10 @@ public abstract class WallpaperService extends Service {
         int mCurWidth;
         int mCurHeight;
         int mWindowFlags = WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE;
+        int mWindowPrivateFlags =
+                WindowManager.LayoutParams.PRIVATE_FLAG_WANTS_OFFSET_NOTIFICATIONS;
         int mCurWindowFlags = mWindowFlags;
+        int mCurWindowPrivateFlags = mWindowPrivateFlags;
         final Rect mVisibleInsets = new Rect();
         final Rect mWinFrame = new Rect();
         final Rect mContentInsets = new Rect();
@@ -359,6 +362,25 @@ public abstract class WallpaperService extends Service {
                 updateSurface(false, false, false);
             }
         }
+
+        /**
+         * Control whether this wallpaper will receive notifications when the wallpaper
+         * has been scrolled. By default, wallpapers will receive notifications, although
+         * the default static image wallpapers do not. It is a performance optimization to
+         * set this to false.
+         *
+         * @param enabled whether the wallpaper wants to receive offset notifications
+         */
+        public void setOffsetNotificationsEnabled(boolean enabled) {
+            mWindowPrivateFlags = enabled
+                    ? (mWindowPrivateFlags |
+                        WindowManager.LayoutParams.PRIVATE_FLAG_WANTS_OFFSET_NOTIFICATIONS)
+                    : (mWindowPrivateFlags &
+                        ~WindowManager.LayoutParams.PRIVATE_FLAG_WANTS_OFFSET_NOTIFICATIONS);
+            if (mCreated) {
+                updateSurface(false, false, false);
+            }
+        }
         
         /**
          * Called once to initialize the engine.  After returning, the
@@ -478,6 +500,8 @@ public abstract class WallpaperService extends Service {
             out.print(prefix); out.print("mType="); out.print(mType);
                     out.print(" mWindowFlags="); out.print(mWindowFlags);
                     out.print(" mCurWindowFlags="); out.println(mCurWindowFlags);
+                    out.print(" mWindowPrivateFlags="); out.print(mWindowPrivateFlags);
+                    out.print(" mCurWindowPrivateFlags="); out.println(mCurWindowPrivateFlags);
             out.print(prefix); out.print("mVisibleInsets=");
                     out.print(mVisibleInsets.toShortString());
                     out.print(" mWinFrame="); out.print(mWinFrame.toShortString());
@@ -528,7 +552,8 @@ public abstract class WallpaperService extends Service {
             final boolean formatChanged = mFormat != mSurfaceHolder.getRequestedFormat();
             boolean sizeChanged = mWidth != myWidth || mHeight != myHeight;
             final boolean typeChanged = mType != mSurfaceHolder.getRequestedType();
-            final boolean flagsChanged = mCurWindowFlags != mWindowFlags;
+            final boolean flagsChanged = mCurWindowFlags != mWindowFlags ||
+                    mCurWindowPrivateFlags != mWindowPrivateFlags;
             if (forceRelayout || creating || surfaceCreating || formatChanged || sizeChanged
                     || typeChanged || flagsChanged || redrawNeeded) {
 
@@ -554,6 +579,8 @@ public abstract class WallpaperService extends Service {
                             | WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN
                             | WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
                             ;
+                    mCurWindowPrivateFlags = mWindowPrivateFlags;
+                    mLayout.privateFlags = mWindowPrivateFlags;
 
                     mLayout.memoryType = mType;
                     mLayout.token = mWindowToken;