Emulate Android joystick scroll with synthetic mouse wheel event

content/public/android/java/src/org/chromium/content/browser/input/JoystickScrollProvider.java

Index: content/public/android/java/src/org/chromium/content/browser/input/JoystickScrollProvider.java
diff --git a/content/public/android/java/src/org/chromium/content/browser/input/JoystickScrollProvider.java b/content/public/android/java/src/org/chromium/content/browser/input/JoystickScrollProvider.java
index 1336b78b3982b6630d0ad30e90bbc4cf88c6ee73..8c57b5f8f8531fb34f99ba8a4890ca492b78903d 100644
--- a/content/public/android/java/src/org/chromium/content/browser/input/JoystickScrollProvider.java
+++ b/content/public/android/java/src/org/chromium/content/browser/input/JoystickScrollProvider.java
@@ -4,17 +4,25 @@
 
 package org.chromium.content.browser.input;
 
+import android.content.Context;
 import android.util.TypedValue;
 import android.view.InputDevice;
 import android.view.MotionEvent;
+import android.view.View;
 import android.view.animation.AnimationUtils;
 
 import org.chromium.base.Log;
-import org.chromium.content.browser.ContentViewCore;
+import org.chromium.base.annotations.CalledByNative;
+import org.chromium.base.annotations.JNINamespace;
+import org.chromium.content_public.browser.WebContents;
+import org.chromium.ui.base.WindowAndroid;
+import org.chromium.ui.display.DisplayAndroid;
+import org.chromium.ui.display.DisplayAndroid.DisplayAndroidObserver;
 
 /**
  * This class implements auto scrolling and panning for gamepad left joystick motion event.
  */
+@JNINamespace("content")
 public class JoystickScrollProvider {
     private static final String TAG = "JoystickScroll";
 
@@ -24,11 +32,26 @@ public class JoystickScrollProvider {
     private static final float JOYSTICK_SCROLL_DEADZONE = 0.2f;
     private static final float SCROLL_FACTOR_FALLBACK = 128f;
 
-    private final ContentViewCore mView;
+    private class JoystickScrollDisplayObserver implements DisplayAndroidObserver {
+        @Override
+        public void onRotationChanged(int rotation) {}
+
+        @Override
+        public void onDIPScaleChanged(float dipScale) {
+            mDipScale = dipScale;
+            updateScrollFactor();
+        }
+    }
+
+    private WindowAndroid mWindowAndroid;
+    private View mContainerView;
+    private long mNativeJoystickScrollProvider;
+    private JoystickScrollDisplayObserver mDisplayObserver;
 
     private float mScrollVelocityX;
     private float mScrollVelocityY;
     private float mScrollFactor;
+    private float mDipScale = 1.0f;
 
     private long mLastAnimateTimeMillis;
 
@@ -38,12 +61,20 @@ public class JoystickScrollProvider {
 
     /**
      * Constructs a new JoystickScrollProvider.
-     *
-     * @param contentview The ContentViewCore used to create this.
      */
-    public JoystickScrollProvider(ContentViewCore contentView) {
-        mView = contentView;
+    public JoystickScrollProvider(
+            WebContents webContents, View containerView, WindowAndroid windowAndroid) {
+        mNativeJoystickScrollProvider = nativeInit(webContents);
+        mContainerView = containerView;
+        mWindowAndroid = windowAndroid;
         mEnabled = true;
+        mDisplayObserver = new JoystickScrollDisplayObserver();
+    }
+
+    @CalledByNative
+    private void onNativeObjectDestroyed(long nativePointer) {
+        assert nativePointer == mNativeJoystickScrollProvider;
+        mNativeJoystickScrollProvider = 0;
     }
 
     /**
@@ -56,6 +87,49 @@ public class JoystickScrollProvider {
         if (!enabled) stop();
     }
 
+    public void onViewAttachedToWindow() {
+        addDisplayAndroidObserver();
+    }
+
+    public void onViewDetachedFromWindow() {
+        removeDisplayAndroidObserver();
+    }
+
+    public void updateWindowAndroid(WindowAndroid windowAndroid) {
+        removeDisplayAndroidObserver();
+        mWindowAndroid = windowAndroid;
+        addDisplayAndroidObserver();
+    }
+
+    private void addDisplayAndroidObserver() {
+        if (mWindowAndroid == null) return;
+
+        DisplayAndroid display = mWindowAndroid.getDisplay();
+        display.addObserver(mDisplayObserver);
+        mDisplayObserver.onDIPScaleChanged(display.getDipScale());
+    }
+
+    private void removeDisplayAndroidObserver() {
+        if (mWindowAndroid == null) return;
+        mWindowAndroid.getDisplay().removeObserver(mDisplayObserver);
+    }
+
+    private void updateScrollFactor() {
+        Context context = mWindowAndroid == null ? null : mWindowAndroid.getContext().get();
+        TypedValue outValue = new TypedValue();
+
+        if (context != null && context.getTheme().resolveAttribute(
+                android.R.attr.listPreferredItemHeight, outValue, true)) {
+            mScrollFactor = outValue.getDimension(context.getResources().getDisplayMetrics());
+        } else {
+            if (context != null) {
+                Log.d(TAG, "Theme attribute listPreferredItemHeight not defined"
+                                + " switching to fallback scroll factor");
+            }
+            mScrollFactor = SCROLL_FACTOR_FALLBACK * mDipScale;
+        }
+    }
+
     /**
      * This function processes motion event and computes new
      * scroll offest in pixels which is propertional to left joystick
@@ -72,7 +146,13 @@ public class JoystickScrollProvider {
         Log.d(TAG, "Joystick left stick axis: " + event.getAxisValue(MotionEvent.AXIS_X) + ","
                 + event.getAxisValue(MotionEvent.AXIS_Y));
 
-        computeNewScrollVelocity(event);
+        assert mScrollFactor != 0;
+
+        mScrollVelocityX = getFilteredAxisValue(event, MotionEvent.AXIS_X) * mScrollFactor
+                * JOYSTICK_SCROLL_FACTOR_MULTIPLIER;
+        mScrollVelocityY = getFilteredAxisValue(event, MotionEvent.AXIS_Y) * mScrollFactor
+                * JOYSTICK_SCROLL_FACTOR_MULTIPLIER;
+
         if (mScrollVelocityX == 0 && mScrollVelocityY == 0) {
             stop();
             return false;
@@ -86,7 +166,7 @@ public class JoystickScrollProvider {
             };
         }
         if (mLastAnimateTimeMillis == 0) {
-            mView.getContainerView().postOnAnimation(mScrollRunnable);
+            mContainerView.postOnAnimation(mScrollRunnable);
             mLastAnimateTimeMillis = AnimationUtils.currentAnimationTimeMillis();
         }
         return true;
@@ -100,9 +180,14 @@ public class JoystickScrollProvider {
         final long dt = timeMillis - mLastAnimateTimeMillis;
         final float dx = (mScrollVelocityX * dt / 1000.f);
         final float dy = (mScrollVelocityY * dt / 1000.f);
-        mView.scrollBy(dx, dy, true);
+
+        if (mNativeJoystickScrollProvider != 0) {
+            nativeScrollBy(
+                    mNativeJoystickScrollProvider, timeMillis, dx / mDipScale, dy / mDipScale);
+        }
+
         mLastAnimateTimeMillis = timeMillis;
-        mView.getContainerView().postOnAnimation(mScrollRunnable);
+        mContainerView.postOnAnimation(mScrollRunnable);
     }
 
     private void stop() {
@@ -110,29 +195,6 @@ public class JoystickScrollProvider {
     }
 
     /**
-     * Translates joystick axes movement to a scroll velocity.
-     */
-    private void computeNewScrollVelocity(MotionEvent event) {
-        if (mScrollFactor == 0) {
-            TypedValue outValue = new TypedValue();
-            if (!mView.getContext().getTheme().resolveAttribute(
-                        android.R.attr.listPreferredItemHeight, outValue, true)) {
-                mScrollFactor = outValue.getDimension(
-                        mView.getContext().getResources().getDisplayMetrics());
-            } else {
-                Log.d(TAG, "Theme attribute listPreferredItemHeight not defined"
-                                + "switching to fallback scroll factor ");
-                mScrollFactor = SCROLL_FACTOR_FALLBACK
-                        * mView.getRenderCoordinates().getDeviceScaleFactor();
-            }
-        }
-        mScrollVelocityX = getFilteredAxisValue(event, MotionEvent.AXIS_X) * mScrollFactor
-                * JOYSTICK_SCROLL_FACTOR_MULTIPLIER;
-        mScrollVelocityY = getFilteredAxisValue(event, MotionEvent.AXIS_Y) * mScrollFactor
-                * JOYSTICK_SCROLL_FACTOR_MULTIPLIER;
-    }
-
-    /**
      * Removes noise from joystick motion events.
      */
     private float getFilteredAxisValue(MotionEvent event, int axis) {
@@ -143,4 +205,8 @@ public class JoystickScrollProvider {
         }
         return 0f;
     }
+
+    private native long nativeInit(WebContents webContents);
+    private native void nativeScrollBy(
+            long nativeJoystickScrollProvider, long timeMs, float dxDip, float dyDip);
 }