Implement Raster Backend on Android Viewer App

platform_tools/android/apps/viewer/src/main/java/org/skia/viewer/StateAdapter.java

Index: platform_tools/android/apps/viewer/src/main/java/org/skia/viewer/StateAdapter.java
diff --git a/platform_tools/android/apps/viewer/src/main/java/org/skia/viewer/StateAdapter.java b/platform_tools/android/apps/viewer/src/main/java/org/skia/viewer/StateAdapter.java
index d546c7bb3e19d520baff1a61efeaebb0ac85621c..9a8646b7cd55f2b0cee45decd0c69001c9606612 100644
--- a/platform_tools/android/apps/viewer/src/main/java/org/skia/viewer/StateAdapter.java
+++ b/platform_tools/android/apps/viewer/src/main/java/org/skia/viewer/StateAdapter.java
@@ -1,6 +1,7 @@
 package org.skia.viewer;
 
 import android.view.LayoutInflater;
+import android.view.SurfaceView;
 import android.view.View;
 import android.view.ViewGroup;
 import android.widget.AdapterView;
@@ -30,6 +31,7 @@ public class StateAdapter extends BaseAdapter implements AdapterView.OnItemSelec
     static final String NAME = "name";
     static final String VALUE = "value";
     static final String OPTIONS = "options";
+    private static final String BACKEND_STATE_NAME = "Backend";
 
     ViewerActivity mViewerActivity;
     LinearLayout mLayout;
@@ -146,6 +148,22 @@ public class StateAdapter extends BaseAdapter implements AdapterView.OnItemSelec
             stateItem.setTag(null); // Reset the tag to let updateDrawer update this item view.
             mViewerActivity.onStateChanged(stateName, stateValue);
         }
+        mViewerActivity.onStateChanged(stateName, stateValue);
+
+        // Due to the current Android limitation, we're required to recreate the SurfaceView for
+        // switching to/from the Raster backend.
+        // (Although we can switch between GPU backend without recreating the SurfaceView.)
+        final Object oldValue = stateItem.getTag(R.integer.value_tag_key);
+        if (stateName.equals(BACKEND_STATE_NAME)
+                && oldValue != null && !stateValue.equals(oldValue)) {
+            LinearLayout mainLayout = (LinearLayout) mViewerActivity.findViewById(R.id.mainLayout);
+            mainLayout.removeAllViews();
+            SurfaceView surfaceView = new SurfaceView(mViewerActivity);
+            surfaceView.setId(R.id.surfaceView);
+            surfaceView.getHolder().addCallback(mViewerActivity);
+            surfaceView.setOnTouchListener(mViewerActivity);
+            mainLayout.addView(surfaceView);
+        }
     }
 
     @Override