exo: Implement wayland gamepad support

components/exo/gamepad.h

+// Copyright 2016 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.
+
+#ifndef COMPONENTS_EXO_GAMEPAD_H_
+#define COMPONENTS_EXO_GAMEPAD_H_
+
+#include <memory>
+
+#include "base/macros.h"
+#include "base/sequenced_task_runner.h"
+#include "base/synchronization/lock.h"
+#include "base/threading/thread.h"
+#include "base/threading/thread_task_runner_handle.h"
+#include "device/gamepad/gamepad_data_fetcher.h"
+#include "ui/aura/client/focus_change_observer.h"
+
+namespace exo {
+class GamepadDelegate;
+
+// This class represents one or more gamepads, it implements a background thread
+// for polling gamepad devices and notifies the GamepadDelegate of any
+// changes.
+class Gamepad : public aura::client::FocusChangeObserver {
+ public:
+  // This class will post tasks to invoke the delegate on the thread runner
+  // which is associated with the thread that is creating this instance.
+  explicit Gamepad(GamepadDelegate* delegate);
+  // Allows test cases to specify a GamepadDataFetcher to provide mock gamepad
+  // data.
+  Gamepad(GamepadDelegate* delegate,
+          std::unique_ptr<device::GamepadDataFetcher> fetcher);
+  virtual ~Gamepad();
+
+  // Overridden aura::client::FocusChangeObserver:
+  void OnWindowFocused(aura::Window* gained_focus,
+                       aura::Window* lost_focus) override;
+
+ private:
+  // Schedules a poll on the polling thread. Can be called from any thread.
+  void ScheduleOnPoll();
+
+  // Polls devices for new data and posts delegate updates.
+  // Can only be called on the polling thread.
+  void OnPoll();
+
+  // Posts updates of gamepad data to delegate.
+  // Can only be called on the polling thread.
+  void PostGamepadChanges(const blink::WebGamepads new_state);
+
+  // Initializes the underlying gamepad data fetcher.
+  // Can only be called on the polling thread.
+  void InitializePollingThread();
+
+  // The delegate instance that all events are dispatched to.
+  GamepadDelegate* const delegate_;
+
+  // Implements the logic to fetch gamepad information from connected devices.
+  // Only used by polling thread.
+  std::unique_ptr<device::GamepadDataFetcher> fetcher_;
+
+  // The current state of gamepad. Only used by polling thread.
+  blink::WebGamepads state_;
+
+  // The thread on which the polling is executed.
+  std::unique_ptr<base::Thread> polling_thread_;
+
+  // True if an exosphere window is currently focused.
+  bool exo_focused_;

[reveman, 2016/06/30 01:19:05]

I don't think this is enough. How do we know that the surface actually belongs
to the client that owns this gamepad instance? I think this needs to be
"Surface* focus_ = nullptr;" and the same logic as keyboard impl.

[denniskempin, 2016/06/30 03:23:43]

I can do the CanAcceptKeyboardEventsForSurface equivalent here, but we can still
just store a boolean for focus or not focus after checking if the delegate
accepts events on that surface. 

[denniskempin, 2016/06/30 17:08:29]

Done.

+
+  // Locks internal state
+  base::Lock lock_;
+
+  // Reference to the task runner of the thread that created this instance.
+  scoped_refptr<base::SingleThreadTaskRunner> origin_task_runner_;
+
+  base::ThreadChecker thread_checker_;

[reveman, 2016/06/30 01:19:05]

I think a thread checker is a good idea but I'm not seeing it used. Did you
forget to update the cc file?

[denniskempin, 2016/06/30 17:08:29]

I used to. With the latest update I changed it to have one thread checker for
the origin and another for the polling thread.

+
+  DISALLOW_COPY_AND_ASSIGN(Gamepad);
+};
+
+}  // namespace exo
+
+#endif  // COMPONENTS_EXO_GAMEPAD_H_