Cache wallpaper bitmap to avoid re-loading on rotation

Screen rotations force static wallpapers to get recreated. One of the things
that happens is that the underlying bitmap resource is loaded. This can be quite
expensive for large bitmaps (which is the case on large-display devices).
A simple optimization is to retain the bitmap in the wallpaper process, to avoid
this re-loading step. We still re-draw and re-upload the texture, but at least
we don't re-load the thing.

Issue #7324823 Manta wallpaper decode performance is atrocious

Change-Id: I0748e275a55992d13704a7dec5910d2dbdc9e2a4

Author: chethaase

packages/SystemUI/src/com/android/systemui/ImageWallpaper.java

@@ -19,6 +19,7 @@
 import android.app.ActivityManager;
 import android.app.WallpaperManager;
 import android.content.BroadcastReceiver;
+import android.content.ComponentCallbacks2;
 import android.content.Context;
 import android.content.Intent;
 import android.graphics.Bitmap;
@@ -62,6 +63,8 @@ public class ImageWallpaper extends WallpaperService {
 
     WallpaperManager mWallpaperManager;
 
+    DrawableEngine mEngine;
+
     boolean mIsHwAccelerated;
 
     @Override
@@ -77,12 +80,20 @@ public void onCreate() {
         }
     }
 
+    @Override
+    public void onTrimMemory(int level) {
+        if (mEngine != null) {
+            mEngine.trimMemory(level);
+        }
+    }
+
     private static boolean isEmulator() {
         return "1".equals(SystemProperties.get(PROPERTY_KERNEL_QEMU, "0"));
     }
 
     public Engine onCreateEngine() {
-        return new DrawableEngine();
+        mEngine = new DrawableEngine();
+        return mEngine;
     }
 
     class DrawableEngine extends Engine {
@@ -155,6 +166,15 @@ public DrawableEngine() {
             setFixedSizeAllowed(true);
         }
 
+        public void trimMemory(int level) {
+            if (level >= ComponentCallbacks2.TRIM_MEMORY_RUNNING_LOW &&
+                    mBackground != null && mIsHwAccelerated) {
+                mBackground.recycle();
+                mBackground = null;
+                mWallpaperManager.forgetLoadedWallpaper();
+            }
+        }
+
         @Override
         public void onCreate(SurfaceHolder surfaceHolder) {
             if (DEBUG) {
@@ -329,16 +349,17 @@ void drawFrameLocked() {
                 }
             } else {
                 drawWallpaperWithCanvas(sh, availw, availh, xPixels, yPixels);
+                if (FIXED_SIZED_SURFACE) {
+                    // If the surface is fixed-size, we should only need to
+                    // draw it once and then we'll let the window manager
+                    // position it appropriately.  As such, we no longer needed
+                    // the loaded bitmap.  Yay!
+                    // hw-accelerated path retains bitmap for faster rotation
+                    mBackground = null;
+                    mWallpaperManager.forgetLoadedWallpaper();
+                }
             }
 
-            if (FIXED_SIZED_SURFACE) {
-                // If the surface is fixed-size, we should only need to
-                // draw it once and then we'll let the window manager
-                // position it appropriately.  As such, we no longer needed
-                // the loaded bitmap.  Yay!
-                mBackground = null;
-                mWallpaperManager.forgetLoadedWallpaper();
-            }
         }
 
         void updateWallpaperLocked() {
@@ -489,8 +510,6 @@ private int loadTexture(Bitmap bitmap) {
             GLUtils.texImage2D(GL_TEXTURE_2D, 0, GL_RGBA, bitmap, GL_UNSIGNED_BYTE, 0);
             checkGlError();
 
-            bitmap.recycle();
-    
             return texture;
         }