Enable smooth scroll/pan through gamepad

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
new file mode 100644
index 0000000000000000000000000000000000000000..1039c689d3478bf3eb7b231d5c7e7d3a65a74180
--- /dev/null
+++ b/content/public/android/java/src/org/chromium/content/browser/input/JoystickScrollProvider.java
@@ -0,0 +1,157 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.content.browser.input;
+
+import android.util.TypedValue;
+import android.view.InputDevice;
+import android.view.MotionEvent;
+import android.view.animation.AnimationUtils;
+
+import org.chromium.base.Log;
+import org.chromium.content.browser.ContentViewCore;
+
+/**
+ * This class implements auto scrolling and panning for gamepad left joystick motion event.
+ */
+public class JoystickScrollProvider {
+    private static final String TAG = "JoystickScrollProvider";
+
+    private static final float JOYSTICK_SCROLL_FACTOR_MULTIPLIER = 25f;
+    // Joystick produces "noise", 0.20f has proven a safe value to
+    // remove noise and still allow reasonable input range.
+    private static final float JOYSTICK_SCROLL_DEADZONE = 0.2f;
+    private static final float SCROLL_FACTOR_FALLBACK = 128f;
+
+    private final ContentViewCore mView;
+
+    private float mScrollVelocityX;
+    private float mScrollVelocityY;
+    private float mScrollFactor;
+
+    private long mLastAnimateTimeMillis;
+
+    private boolean mAutoScrollActive;
+
+    private boolean mEnabled;
+
+    private Runnable mScrollRunnable;
+
+    /**
+     * Constructs a new JoystickScrollProvider.
+     *
+     * @param contentview The ContentViewCore used to create this.
+     */
+    public JoystickScrollProvider(ContentViewCore contentView) {
+        mView = contentView;
+        mAutoScrollActive = false;
+        mEnabled = true;
+    }
+
+    /**
+     * This function enables or disables scrolling through joystick.
+     * @param enabled Decides whether joystick scrolling should be
+     *                enabled or not.
+     */
+    public void setEnabled(boolean enabled) {
+        mEnabled = enabled;
+        if (!enabled) stop();
+    }
+
+    /**
+     * This function processes motion event and computes new
+     * scroll offest in pixels which is propertional to left joystick
+     * axes movement.
+     * It also starts runnable to scroll content view core equal to
+     * scroll offset pixels.
+     *
+     * @param event Motion event to be processed for scrolling.
+     * @return Whether scrolling using left joystick is performed or not.
+     */
+    public boolean onMotion(MotionEvent event) {
+        if (!mEnabled) return false;
+        if ((event.getSource() & InputDevice.SOURCE_CLASS_JOYSTICK) == 0) return false;
+
+        computeNewScrollVelocity(event);
+        if (mScrollVelocityX == 0 && mScrollVelocityY == 0) {
+            stop();
+            return false;
+        }
+        if (mScrollRunnable == null) {
+            mScrollRunnable = new Runnable() {
+                @Override
+                public void run() {
+                    animateScroll();
+                }
+            };
+        }
+        if (!mAutoScrollActive) {
+            mView.getContainerView().postOnAnimation(mScrollRunnable);
+            mAutoScrollActive = true;
+        }
+        return true;
+    }
+
+    private void animateScroll() {
+        if (!mEnabled || !mView.getContainerView().hasFocus()) {
+            stop();
+            return;
+        }
+
+        final long timeMillis = AnimationUtils.currentAnimationTimeMillis();
+        if (mLastAnimateTimeMillis != 0 && timeMillis > mLastAnimateTimeMillis) {
+            final long dt = timeMillis - mLastAnimateTimeMillis;
+            final float dx = (mScrollVelocityX * dt / 1000.f);
+            final float dy = (mScrollVelocityY * dt / 1000.f);
+            mView.scrollBy(dx, dy, true);
+        }
+        assert mAutoScrollActive;
+        mLastAnimateTimeMillis = timeMillis;
+        mView.getContainerView().postOnAnimation(mScrollRunnable);
+    }
+
+    private void stop() {
+        mLastAnimateTimeMillis = 0;
+        if (mAutoScrollActive) {
+            mAutoScrollActive = false;
+            mView.getContainerView().removeCallbacks(mScrollRunnable);
+        }
+    }
+
+    /**
+     * 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.w(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) {
+        float axisValWithNoise = event.getAxisValue(axis);
+        if (axisValWithNoise > JOYSTICK_SCROLL_DEADZONE) {
+            return axisValWithNoise - JOYSTICK_SCROLL_DEADZONE;
+        } else if (axisValWithNoise < -JOYSTICK_SCROLL_DEADZONE) {
+            return axisValWithNoise + JOYSTICK_SCROLL_DEADZONE;
+        }
+        return 0f;
+    }
+}