Use swipe gesture to switch between slides on Android

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

Index: platform_tools/android/apps/viewer/src/main/java/org/skia/viewer/ViewerActivity.java
diff --git a/platform_tools/android/apps/viewer/src/main/java/org/skia/viewer/ViewerActivity.java b/platform_tools/android/apps/viewer/src/main/java/org/skia/viewer/ViewerActivity.java
index 48cec39f483d658970297cc17813b460b75dc53b..e115de65b32bed8113f80de5b0f471b618753a70 100644
--- a/platform_tools/android/apps/viewer/src/main/java/org/skia/viewer/ViewerActivity.java
+++ b/platform_tools/android/apps/viewer/src/main/java/org/skia/viewer/ViewerActivity.java
@@ -9,17 +9,50 @@ package org.skia.viewer;
 
 import android.app.Activity;
 import android.os.Bundle;
+import android.util.Log;
+import android.view.GestureDetector;
+import android.view.KeyEvent;
+import android.view.MotionEvent;
 import android.view.Surface;
 import android.view.SurfaceHolder;
 import android.view.SurfaceView;
+import android.view.View;
+
+public class ViewerActivity
+        extends Activity implements SurfaceHolder.Callback, View.OnTouchListener {
+    private static final float FLING_VELOCITY_THRESHOLD = 1000;
 
-public class ViewerActivity extends Activity implements SurfaceHolder.Callback {
     private SurfaceView mView;
     private ViewerApplication mApplication;
+    private GestureDetector mGestureDetector;
 
     private native void onSurfaceCreated(long handle, Surface surface);
     private native void onSurfaceChanged(long handle, Surface surface);
     private native void onSurfaceDestroyed(long handle);
+    private native void onKeyPressed(long handle, int keycode);
+
+    private class GestureListener extends GestureDetector.SimpleOnGestureListener {
+        @Override
+        public boolean onDown(MotionEvent e) {
+            return true;
+        }
+
+        @Override
+        public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
+            if (Math.abs(velocityX) > Math.abs(velocityY)
+                && Math.abs(velocityX) > FLING_VELOCITY_THRESHOLD) {
+                if (velocityX > 0) {
+                    // Fling right
+                    onKeyPressed(mApplication.getNativeHandle(), KeyEvent.KEYCODE_SOFT_RIGHT);
+                } else {
+                    // Fling left
+                    onKeyPressed(mApplication.getNativeHandle(), KeyEvent.KEYCODE_SOFT_LEFT);
+                }
+                return true;
+            }
+            return false;
+        }
+    }
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {
@@ -29,6 +62,9 @@ public class ViewerActivity extends Activity implements SurfaceHolder.Callback {
         mApplication = (ViewerApplication) getApplication();
         mView = (SurfaceView) findViewById(R.id.surfaceView);
         mView.getHolder().addCallback(this);
+
+        mGestureDetector = new GestureDetector(getApplicationContext(), new GestureListener());
+        mView.setOnTouchListener(this);
     }
 
     @Override
@@ -51,4 +87,9 @@ public class ViewerActivity extends Activity implements SurfaceHolder.Callback {
             onSurfaceDestroyed(mApplication.getNativeHandle());
         }
     }
+
+    @Override
+    public boolean onTouch(View v, MotionEvent event) {
+        return mGestureDetector.onTouchEvent(event);
+    }
 }