Gamepad API for Android

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

+// Copyright 2014 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.content.Context;
+import android.hardware.input.InputManager;
+import android.view.InputDevice;
+import android.view.InputDevice.MotionRange;
+import android.view.KeyEvent;
+import android.view.MotionEvent;
+
+import org.chromium.base.CalledByNative;
+import org.chromium.base.JNINamespace;
+import org.chromium.base.ThreadUtils;
+
+import java.util.List;
+
+/**
+ * Java counterpart of GamepadPlatformDataFetcherAndroid.
+ * Manages game input devices and feed Gamepad API with input data.
+ * GamepadPlatformDataFetcherAndroid is merely a wrepper around this.
+ * Native callable methods called by GamepadPlatformDataFetcherAndroid on the poller thread
+ * which is a native thread without a java looper. Events are processed on the UI thread.
+ */
+@JNINamespace("content")
+public class GamepadAdapter implements InputManager.InputDeviceListener {
+
+    private static final int NUM_WEB_GAMEPADS = 4;
+
+    private static GamepadAdapter instance;
+
+    private InputManager mInputManager;
+    private InputDeviceHandler[] mDeviceHandlers;
+    private final Object mDeviceHandlersLock = new Object();
+    private boolean mDataRequested;
+    private boolean mIsPaused;
+    private long mNativeDataFetcher;
+    private int mAttachedToWindowCounter;
+
+    private static void initializeInstance() {
+        if (instance == null) {
+            instance = new GamepadAdapter();
+        }
+    }
+
+    /**
+     * Notifies GamepadAdapter that a {@link ContentView} is attached to a window so it should
+     * be prepared for input. Must be called before {@link onMotionEvent} or {@link onKeyEvent}.
+     */
+    public static void onAttachedToWindow(Context context) {
+        assert ThreadUtils.runningOnUiThread();
+        initializeInstance();
+        instance.attachedToWindow(context);
+    }
+
+    private void attachedToWindow(Context context) {
+        if (mAttachedToWindowCounter++ == 0) {
+            mInputManager = (InputManager) context.getSystemService(Context.INPUT_SERVICE);
+            if (mInputManager != null) {

[boliu, 2014/03/12 00:58:46]

You'd need to null check everywhere mInputManager is used...

Actually getSystemService is called all over the place without null checks, so
if there really are issues, this won't be the only place. So ignore my comment
about null checks and revert this. Sorry about that.

[kbalazs, 2014/03/12 23:33:50]

Done.

+                initializeDevices();
+                mInputManager.registerInputDeviceListener(this, null);
+            }
+        }
+    }
+
+    private static boolean isAttached() {
+        return instance != null && instance.mAttachedToWindowCounter > 0;
+    }
+
+    /**
+     * Notifies GamepadAdapter that a {@link ContentView} is detached from it's window.
+     */
+    public static void onDetachedFromWindow() {
+        assert ThreadUtils.runningOnUiThread();
+        assert isAttached();
+        instance.detachedFromWindow();
+    }
+
+    private void detachedFromWindow() {
+        if (--mAttachedToWindowCounter == 0) {
+            synchronized (mDeviceHandlersLock) {
+                for (int i = 0; i < NUM_WEB_GAMEPADS; i++) {
+                    mDeviceHandlers[i] = null;
+                }
+            }
+            mInputManager.unregisterInputDeviceListener(this);
+            mInputManager = null;
+        }
+    }
+
+    private void initializeDevices() {
+        assert ThreadUtils.runningOnUiThread();
+        InputDeviceHandler[] handlers = new InputDeviceHandler[NUM_WEB_GAMEPADS];
+        int[] ids = mInputManager.getInputDeviceIds();
+        if (ids == null) return;
+
+        int activeDevices = 0;
+        for (int i = 0; i < ids.length && activeDevices < NUM_WEB_GAMEPADS; i++) {
+            InputDevice device = mInputManager.getInputDevice(ids[i]);
+            if (isGameDevice(device)) {
+                handlers[activeDevices++] = new InputDeviceHandler(device);
+            }
+        }
+        synchronized (mDeviceHandlersLock) {
+            mDeviceHandlers = handlers;
+        }
+    }
+
+    // ---------------------------------------------------
+    // Implementation of InputManager.InputDeviceListener.
+    @Override
+    public void onInputDeviceAdded(int deviceId) {
+        ThreadUtils.assertOnUiThread();
+        InputDevice device = mInputManager.getInputDevice(deviceId);
+        if (!isGameDevice(device))
+            return;
+        int index = nextAvailableIndex();
+        if (index == -1)
+            return;
+        synchronized (mDeviceHandlersLock) {
+            mDeviceHandlers[index] = new InputDeviceHandler(device);
+        }
+    }
+
+    @Override
+    public void onInputDeviceRemoved(int deviceId) {
+        ThreadUtils.assertOnUiThread();
+        int index = indexForDeviceId(deviceId);
+        if (index == -1)
+            return;
+        synchronized (mDeviceHandlersLock) {
+            mDeviceHandlers[index] = null;
+        }
+    }
+
+    @Override
+    public void onInputDeviceChanged(int deviceId) {
+        ThreadUtils.assertOnUiThread();
+        int index = indexForDeviceId(deviceId);
+        if (index == -1) {
+            index = nextAvailableIndex();
+            if (index == -1) return;
+        }
+        InputDevice device = mInputManager.getInputDevice(deviceId);
+        synchronized (mDeviceHandlersLock) {
+            mDeviceHandlers[index] = null;
+            if (isGameDevice(device)) {
+                mDeviceHandlers[index] = new InputDeviceHandler(device);
+            }
+        }
+    }
+    // ---------------------------------------------------
+
+    /**
+     * Handles motion events from gamepad devices.
+     *
+     * @return True if the event has been consumed.
+     */
+    public static boolean onMotionEvent(MotionEvent event) {
+        assert isAttached();
+        return instance.handleMotionEvent(event);
+    }
+
+    private boolean handleMotionEvent(MotionEvent event) {
+        if (!mDataRequested) return false;

[jdduke (slow), 2014/03/12 01:06:19]

I'm a little concerned about the event flow when |mDataRequested| is false.  In
that case, we ignore all of the additional input events, but at the same time we
haven't actually reset the data in |InputDeviceHandler|. That may contain some
potentially stale state, which will linger until processing is resumed, e.g., if
we pause capture while buttons are down, we might have miss the "button up"
event, and when capture resumes we'll continue reporting that the button is
down.

[kbalazs, 2014/03/12 23:33:50]

Good point, trying to handle this now.

+        InputDeviceHandler handler = handlerForDeviceId(event.getDeviceId());
+        if (handler == null) return false;
+        if (!isGameEvent(event)) return false;
+
+        handler.handleMotionEvent(event);
+        return true;
+    }
+
+    /**
+     * Handles key events from gamepad devices.
+     *
+     * @return True if the event has been consumed.
+     */
+    public static boolean onKeyEvent(KeyEvent event) {
+        assert isAttached();
+        return instance.handleKeyEvent(event);
+    }
+
+    private boolean handleKeyEvent(KeyEvent event) {
+        if (!mDataRequested) return false;
+        if (event.getAction() != KeyEvent.ACTION_DOWN
+                && event.getAction() != KeyEvent.ACTION_UP) {
+            return false;
+        }
+        InputDeviceHandler handler = handlerForDeviceId(event.getDeviceId());
+        if (handler == null) return false;
+        int keyCode = event.getKeyCode();
+        if (!isGameKey(keyCode)) return false;
+
+        boolean isDown = event.getAction() == KeyEvent.ACTION_DOWN;
+        handler.handleKeyEvent(keyCode, isDown, event.getEventTime());
+        return true;
+    }
+
+    @CalledByNative
+    static void setDataRequested(long nativeDataFetcher, boolean requested) {
+        initializeInstance();
+        instance.mNativeDataFetcher = nativeDataFetcher;

[jdduke (slow), 2014/03/12 01:06:19]

Hmm, we should not be caching the |nativeDataFetcher|.   |getGamepadData| should
take as an argument the native pointer to the |blink::WebGamepads* pads|,
calling back into a static function to populate the |pads| object directly.  In
short, we shouldn't need to store *any* native pointers in this class.

[kbalazs, 2014/03/12 23:33:50]

Done.

+        instance.mDataRequested = requested;
+    }
+
+    // Called on polling thread.
+    @CalledByNative
+    static void getGamepadData() {
+        assert instance != null;
+        instance.collectGamepadData();
+    }
+
+    private void collectGamepadData() {
+        assert mNativeDataFetcher != 0;
+        mDataRequested = true;

[jdduke (slow), 2014/03/12 01:06:19]

This variable is accessed on the UI thread, it should be protected.  Are you
setting it to true here to signal the start of collection, potentially missing
the initial set of data on the first call? That's not a huge deal, I just want
to be clear about the motivation.

[kbalazs, 2014/03/12 23:33:50]

There are in fact a race with the UI thread about this variable but I cannot
think about a way that it could cause any problems We just delay the data on
more frame in worst case. Now that I added clearInput() to avoid the potentional
anomalies you pointed out it got trickier but I think it's still ok without
locking. I added a long comment about that.

The motivation of setDataRequested is just to add an implementation for
PlatformDataFetcher::PauseHint. It is supposed to be an optimization. It is
probably not that useful. We can early return instead of processing the events
but the processing is fast anyway. However I think there is another reason it
might be necessary: it's probably not ok to consume the events and stop further
dispatching when the web page doesn't observe gamepad data.

+        synchronized (mDeviceHandlersLock) {
+            for (int i = 0; i < NUM_WEB_GAMEPADS; i++) {
+                if (mDeviceHandlers[i] == null) {

[jdduke (slow), 2014/03/12 01:06:19]

Just so I understand this correctly, if |collectGamepadData| is called multiples
times in succession, without additional input, the same set of data should be
returned?  In that case, |reportGamepadData| might be a little more clear to
indicate that that the "collecting" is non-destructive and read-only.

[kbalazs, 2014/03/12 23:33:50]

Done.

+                    nativeRefreshDevice(mNativeDataFetcher, i, false, null, null, 0, null, null);
+                } else {
+                    InputDeviceHandler handler = mDeviceHandlers[i];
+                    WebGamepadData data = handler.produceWebData();
+                    nativeRefreshDevice(mNativeDataFetcher, i, true, data.id, data.mapping,
+                            handler.getTimestamp(), data.axes, data.buttons);
+                }
+            }
+        }
+    }
+
+    private int nextAvailableIndex() {
+        for (int i = 0; i < mDeviceHandlers.length; i++) {
+            if (mDeviceHandlers[i] == null)
+                return i;
+        }
+        return -1;
+    }
+
+    private int indexForDeviceId(int deviceId) {
+        for (int i = 0; i < mDeviceHandlers.length; i++) {
+            if (mDeviceHandlers[i] != null &&
+                mDeviceHandlers[i].getInputDevice().getId() == deviceId)
+                return i;
+        }
+        return -1;
+    }
+
+    private InputDeviceHandler handlerForDeviceId(int deviceId) {
+        int index = indexForDeviceId(deviceId);
+        return index == -1 ? null : mDeviceHandlers[index];
+    }
+
+    private static boolean isGameDevice(InputDevice device) {
+        return (device.getSources() & InputDevice.SOURCE_JOYSTICK) != 0;
+    }
+
+    private static boolean isGameEvent(MotionEvent event) {
+        return (event.getSource() & InputDevice.SOURCE_JOYSTICK) != 0
+                    && event.getAction() == MotionEvent.ACTION_MOVE;
+    }
+
+    private static boolean isGameKey(int keyCode) {
+        switch (keyCode) {
+            case KeyEvent.KEYCODE_DPAD_UP:
+            case KeyEvent.KEYCODE_DPAD_DOWN:
+            case KeyEvent.KEYCODE_DPAD_LEFT:
+            case KeyEvent.KEYCODE_DPAD_RIGHT:
+            case KeyEvent.KEYCODE_DPAD_CENTER:
+                return true;
+            default:
+                return KeyEvent.isGamepadButton(keyCode);
+        }
+    }
+
+    private static class InputDeviceHandler {
+        private final InputDevice mDevice;
+        private long mTimestamp;
+        private final int[] mAxes;
+
+        // Apparently all axis id's and keycodes are less then 256. Given this the most effective
+        // representation of an associative array is simply an array.
+        private final float[] mAxisValues = new float[256];
+        private final boolean[] mButtonsPressedStates = new boolean[256];
+
+        private final GamepadDataMapper mMapper;
+        private final Object mLock = new Object();
+
+        InputDevice getInputDevice() { return mDevice; }
+        long getTimestamp() { return mTimestamp; }
+
+        InputDeviceHandler(InputDevice device) {
+            assert isGameDevice(device);
+            mDevice = device;
+            mMapper = GamepadDataMapper.createDataMapper(device.getName());
+
+            List<MotionRange> ranges = device.getMotionRanges();
+            mAxes = new int[ranges.size()];
+            int i = 0;
+            for (MotionRange range : ranges) {
+                if ((range.getSource() & InputDevice.SOURCE_CLASS_JOYSTICK) != 0) {
+                    int axis = range.getAxis();
+                    assert axis < 256;
+                    mAxes[i++] = axis;
+                }
+            }
+        }
+
+        // Called on UI thread.
+        void handleMotionEvent(MotionEvent event) {
+            synchronized (mLock) {
+                mTimestamp = event.getEventTime();
+                for (int i = 0; i < mAxes.length; i++) {
+                    int axis = mAxes[i];
+                    mAxisValues[axis] = event.getAxisValue(axis);
+                }
+            }
+        }
+
+        // Called on UI thread.
+        void handleKeyEvent(int keyCode, boolean isDown, long timestamp) {
+            synchronized (mLock) {
+                mTimestamp = timestamp;
+                assert keyCode < 256;
+                mButtonsPressedStates[keyCode] = isDown;
+            }
+        }
+
+        // Called on polling thread.
+        WebGamepadData produceWebData() {
+            synchronized (mLock) {
+                return mMapper.map(mAxisValues, mButtonsPressedStates);
+            }
+        }
+    }
+
+    private native void nativeRefreshDevice(long nativeGamepadPlatformDataFetcherAndroid,
+            int index, boolean connected, String id, String mapping, long timestamp,
+            float[] axes, float[] buttons);
+}