默认开启“停用HW叠加层”开关，强制GPU渲染

Android开发者模式的选项中有一项叫“停用HW叠加层”，这个选项使能之后，系统所有的UI合成都会全部强制GPU去完成，HWC不再参与合成，需求来源就是默认要使能该功能，即禁用HW叠加，具体实现如下：

diff --git a/src/com/android/settings/FallbackHome.java b/src/com/android/settings/FallbackHome.java
index e3944a65c6..5e7e0cae59 100644
--- a/src/com/android/settings/FallbackHome.java
+++ b/src/com/android/settings/FallbackHome.java
@@ -17,6 +17,7 @@package com.android.settings;import android.app.Activity;
+import android.app.AppGlobals;import android.app.WallpaperColors;import android.app.WallpaperManager;import android.app.WallpaperManager.OnColorsChangedListener;
@@ -25,7 +26,12 @@ import android.content.Context;import android.content.Intent;import android.content.IntentFilter;import android.content.pm.ResolveInfo;
+import android.content.pm.IPackageManager;import android.os.AsyncTask;
+import android.os.IBinder;
+import android.os.Parcel;
+import android.os.RemoteException;
+import android.os.ServiceManager;import android.os.Bundle;import android.os.Handler;import android.os.Message;
@@ -48,6 +54,13 @@ public class FallbackHome extends Activity {private boolean mProvisioned;private WallpaperManager mWallManager;+    private static final int SETTING_VALUE_ON = 1;
+    private static final String SURFACE_FLINGER_SERVICE_KEY = "SurfaceFlinger";
+    private static final String SURFACE_COMPOSER_INTERFACE_KEY = "android.ui.ISurfaceComposer";
+    private static final int SURFACE_FLINGER_DISABLE_OVERLAYS_CODE = 1008;
+
+       private static IBinder mSurfaceFlinger;
+private final Runnable mProgressTimeoutRunnable = () -> {View v = getLayoutInflater().inflate(R.layout.fallback_home_finishing_boot, null /* root */);
@@ -100,10 +113,36 @@ public class FallbackHome extends Activity {}getWindow().getDecorView().setSystemUiVisibility(flags);+        if (mSurfaceFlinger == null) {
+            mSurfaceFlinger = ServiceManager.getService(SURFACE_FLINGER_SERVICE_KEY);
+        }
+
+        initHardwareOverlaysSetting(SETTING_VALUE_ON);
+registerReceiver(mReceiver, new IntentFilter(Intent.ACTION_USER_UNLOCKED));maybeFinish();}+    public void initHardwareOverlaysSetting(int val) {
+        if (mSurfaceFlinger == null) {
+            return;
+        }
+
+        IPackageManager pm = AppGlobals.getPackageManager();
+        // magic communication with surface flinger.
+        try {
+            if (pm.isFirstBoot()) {
+                final Parcel data = Parcel.obtain();
+                data.writeInterfaceToken(SURFACE_COMPOSER_INTERFACE_KEY);
+                data.writeInt(val);
+                mSurfaceFlinger.transact(SURFACE_FLINGER_DISABLE_OVERLAYS_CODE, data, null, 0 /* flags */);
+                data.recycle();
+            }
+        } catch (RemoteException ex) {
+            // intentional no-op
+        }
+    }
+@Overrideprotected void onResume() {super.onResume();

因为开机默认状态，不会加载开发者模式的页面，因此在开发者模式的控制类是无法修改默认的，只能在开机必走的阶段执行使能，这里我选择的是FallbackHome这个类，每次在launcher启动之前都会调用这里，故选择该类。

编译验证，刷机即可发现在开发者选项中，该项值已经默认打开了。