exo: Implement wayland gamepad support

components/exo/gamepad.cc

+// 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.
+
+#include "components/exo/gamepad.h"
+
+#include <cmath>
+
+#include "ash/shell.h"
+#include "base/bind.h"
+#include "base/location.h"
+#include "base/single_thread_task_runner.h"
+#include "base/threading/thread.h"
+#include "base/threading/thread_task_runner_handle.h"
+#include "components/exo/gamepad_delegate.h"
+#include "components/exo/shell_surface.h"
+#include "components/exo/surface.h"
+#include "device/gamepad/gamepad_data_fetcher.h"
+#include "device/gamepad/gamepad_platform_data_fetcher.h"
+#include "ui/aura/client/focus_client.h"
+#include "ui/aura/window.h"
+
+namespace exo {
+namespace {
+
+constexpr double kGamepadButtonValueEpsilon = 0.001;
+bool GamepadButtonValuesAreEqual(double a, double b) {
+  return fabs(a - b) < kGamepadButtonValueEpsilon;
+}
+
+// Time between gamepad polls in milliseconds.
+constexpr unsigned kPollingTimeIntervalMs = 16;
+
+}  // namespace
+
+////////////////////////////////////////////////////////////////////////////////
+// Gamepad::PollingThreadResources
+
+// Implements all methods and resources running on the polling thread.
+// This class is reference counted to allow it to shut down safely on the
+// polling thread even if the Gamepad has been destroyed on the origin thread.
+class Gamepad::PollingThreadResources

[reveman, 2016/07/11 10:50:44]

nit: this class contains more than some resources. it has all the logic for
fetching gamepad changes afaict. can we rename this to
Gamepad::ThreadSafeGamepadChangeFetcher to make this more clear?

[denniskempin, 2016/07/11 17:43:28]

Done.

+    : public base::RefCounted<Gamepad::PollingThreadResources> {

[reveman, 2016/07/11 10:50:44]

Does this need to be base::ThreadSafeRefCounted?

[denniskempin, 2016/07/11 17:43:28]

Done.

+ public:
+  typedef base::Callback<void(const blink::WebGamepad)>
+      PostGamepadChangesCallback;

[reveman, 2016/07/11 10:50:44]

nit: using HandleGamepadChangesCallback = ..

[denniskempin, 2016/07/11 17:43:28]

Done.

+
+  PollingThreadResources(
+      const PostGamepadChangesCallback& post_gamepad_changes,
+      const GamepadDataFetcherFactory& fetcher_factory,
+      const scoped_refptr<base::SingleThreadTaskRunner>& task_runner)

[reveman, 2016/07/11 10:50:44]

nit: different parts of chrome does this differently but I prefer to avoid
ref-counting chrun using "base::SingleThreadTaskRunner* task_runner" instead of
"const scoped_refptr<X>&"

[denniskempin, 2016/07/11 17:43:28]

Done.

+      : post_gamepad_changes_(post_gamepad_changes),
+        fetcher_factory_(fetcher_factory),
+        polling_task_runner_(task_runner),
+        origin_task_runner_(base::ThreadTaskRunnerHandle::Get()) {
+    thread_checker_.DetachFromThread();
+  }
+
+  // Enable or disable gamepad polling. Can be called from any thread.
+  void EnablePolling(bool enabled) {
+    polling_task_runner_->PostTask(
+        FROM_HERE,
+        base::Bind(&PollingThreadResources::EnablePollingOnPollingThread,
+                   make_scoped_refptr(this), enabled));
+  }
+
+ private:
+  friend class base::RefCounted<PollingThreadResources>;
+  virtual ~PollingThreadResources() {}

[reveman, 2016/07/11 10:50:44]

nit: blank line before this

[denniskempin, 2016/07/11 17:43:28]

Done.

+
+  // Enables or disables polling.
+  void EnablePollingOnPollingThread(bool enabled) {
+    DCHECK(thread_checker_.CalledOnValidThread());
+
+    if (enabled == is_enabled_)

[reveman, 2016/07/11 10:50:44]

nit: is this check needed?

[denniskempin, 2016/07/11 17:43:28]

Done.

+      return;
+    is_enabled_ = enabled;
+
+    if (is_enabled_)
+      SchedulePollOnPollingThread();
+  }
+
+  // Schedules the next poll on the polling thread.
+  void SchedulePollOnPollingThread() {
+    DCHECK(thread_checker_.CalledOnValidThread());
+    if (!is_enabled_) {

[reveman, 2016/07/11 10:50:44]

is this needed? if it is, then shouldn't the conditional on l.79 be removed? or
maybe better, do fetcher_.reset() from there? and in that case also create the
fetcher from there.

[denniskempin, 2016/07/11 17:43:28]

Done. I've moved the creation/destruction of the fetcher to the
EnablePollingOnPollingThread method. 

+      fetcher_.reset();
+      return;
+    }
+
+    if (has_poll_scheduled_)
+      return;
+
+    if (!fetcher_) {
+      fetcher_ = fetcher_factory_.Run();
+      DCHECK(fetcher_);
+    }
+
+    has_poll_scheduled_ = true;
+    polling_task_runner_->PostDelayedTask(
+        FROM_HERE, base::Bind(&PollingThreadResources::PollOnPollingThread,
+                              make_scoped_refptr(this)),
+        base::TimeDelta::FromMilliseconds(kPollingTimeIntervalMs));
+  }
+
+  // Polls devices for new data and posts gamepad changes back to origin thread.
+  void PollOnPollingThread() {
+    DCHECK(thread_checker_.CalledOnValidThread());
+    DCHECK(fetcher_);
+    blink::WebGamepads new_state = state_;
+

[reveman, 2016/07/11 10:50:44]

nit: move this blank line above l.110 instead

[denniskempin, 2016/07/11 17:43:28]

Done.

+    fetcher_->GetGamepadData(&new_state, false);
+
+    if (std::max(new_state.length, state_.length) > 0) {
+      if (new_state.items[0].connected != state_.items[0].connected ||
+          new_state.items[0].timestamp > state_.items[0].timestamp) {
+        origin_task_runner_->PostTask(
+            FROM_HERE, base::Bind(post_gamepad_changes_, new_state.items[0]));
+      }
+    }
+
+    state_ = new_state;
+    has_poll_scheduled_ = false;
+    SchedulePollOnPollingThread();
+  }
+
+  // Callback to PostGamepadChanges using weak reference to Gamepad.
+  PostGamepadChangesCallback post_gamepad_changes_;
+
+  // Factory method to create a gamepad data fetcher. Defaults to creating
+  // a PlatformGamepadDataFetcher instance, but can be overwritten for
+  // testing purposes.
+  GamepadDataFetcherFactory fetcher_factory_;

[reveman, 2016/07/11 10:50:44]

nit: create_fetcher_callback_

[denniskempin, 2016/07/11 17:43:28]

Done.

+
+  // Reference to task runner on polling thread.
+  scoped_refptr<base::SingleThreadTaskRunner> polling_task_runner_;
+
+  // Reference to task runner on polling thread.
+  scoped_refptr<base::SingleThreadTaskRunner> origin_task_runner_;
+
+  // Gamepad data fetcher used for querying gamepad devices.
+  std::unique_ptr<device::GamepadDataFetcher> fetcher_;
+
+  // The current state of all gamepads.
+  blink::WebGamepads state_;
+
+  // True if a poll has been scheduled.
+  bool has_poll_scheduled_{false};

[reveman, 2016/07/11 10:50:44]

nit: "has_poll_scheduled_ = false" is preferred in exo and chromium code

[denniskempin, 2016/07/11 17:43:28]

Done.

+
+  // True if the polling thread is paused.
+  bool is_enabled_{true};

[reveman, 2016/07/11 10:50:44]

nit: is_enabled_ = true

[denniskempin, 2016/07/11 17:43:28]

Done.

+
+  // ThreadChecker for the polling thread.
+  base::ThreadChecker thread_checker_;
+
+  DISALLOW_COPY_AND_ASSIGN(PollingThreadResources);
+};
+
+////////////////////////////////////////////////////////////////////////////////
+// Gamepad, public:
+
+Gamepad::Gamepad(
+    GamepadDelegate* delegate,
+    scoped_refptr<base::SingleThreadTaskRunner> polling_task_runner)
+    : Gamepad(delegate,
+              polling_task_runner,
+              base::Bind(Gamepad::GamepadPlatformDataFetcherFactory)) {}
+
+Gamepad::Gamepad(
+    GamepadDelegate* delegate,
+    scoped_refptr<base::SingleThreadTaskRunner> polling_task_runner,
+    GamepadDataFetcherFactory fetcher_factory)
+    : delegate_(delegate), weak_factory_(this) {
+  polling_thread_resources_ = new PollingThreadResources(
+      base::Bind(&Gamepad::PostGamepadChanges, weak_factory_.GetWeakPtr()),
+      fetcher_factory, polling_task_runner);
+
+  aura::client::FocusClient* focus_client =
+      aura::client::GetFocusClient(ash::Shell::GetPrimaryRootWindow());
+  focus_client->AddObserver(this);
+  OnWindowFocused(focus_client->GetFocusedWindow(), nullptr);
+}
+
+Gamepad::~Gamepad() {
+  // Disable polling. Since PollingThreadResources are reference counted, we
+  // can safely have it shut down after Gamepad has been destroyed.
+  polling_thread_resources_->EnablePolling(false);
+
+  delegate_->OnGamepadDestroying(this);
+  aura::client::GetFocusClient(ash::Shell::GetPrimaryRootWindow())
+      ->RemoveObserver(this);
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// aura::client::FocusChangeObserver overrides:
+
+void Gamepad::OnWindowFocused(aura::Window* gained_focus,
+                              aura::Window* lost_focus) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  Surface* target = nullptr;
+  if (gained_focus) {
+    target = Surface::AsSurface(gained_focus);
+    if (!target) {
+      aura::Window* top_level_window = gained_focus->GetToplevelWindow();
+      if (top_level_window)
+        target = ShellSurface::GetMainSurface(top_level_window);
+    }
+  }
+
+  bool focused = target && delegate_->CanAcceptGamepadEventsForSurface(target);
+  if (focused) {

[reveman, 2016/07/11 10:50:44]

nit: polling_thread_resources_->EnablePolling(focused) instead of this if
statement. maybe even remove the temporary |focused| variable.

[denniskempin, 2016/07/11 17:43:28]

Done. Yes.. well this was just dumb ;) 

+    polling_thread_resources_->EnablePolling(true);
+  } else {
+    polling_thread_resources_->EnablePolling(false);
+  }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Gamepad, private:
+
+void Gamepad::PostGamepadChanges(const blink::WebGamepad new_pad) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  bool send_frame = false;
+
+  // Update connection state.
+  if (new_pad.connected != pad_state_.connected) {
+    delegate_->OnStateChange(new_pad.connected);
+  }
+
+  if (!new_pad.connected || new_pad.timestamp <= pad_state_.timestamp) {
+    pad_state_ = new_pad;
+    return;
+  }
+
+  // Notify delegate of updated axes.
+  for (size_t axis = 0;
+       axis < std::max(pad_state_.axesLength, new_pad.axesLength); ++axis) {
+    if (!GamepadButtonValuesAreEqual(new_pad.axes[axis],
+                                     pad_state_.axes[axis])) {
+      send_frame = true;
+      delegate_->OnAxis(axis, new_pad.axes[axis]);
+    }
+  }
+
+  // Notify delegate of updated buttons.
+  for (size_t button_id = 0;
+       button_id < std::max(pad_state_.buttonsLength, new_pad.buttonsLength);
+       ++button_id) {
+    auto button = pad_state_.buttons[button_id];
+    auto new_button = new_pad.buttons[button_id];
+    if (button.pressed != new_button.pressed ||
+        !GamepadButtonValuesAreEqual(button.value, new_button.value)) {
+      send_frame = true;
+      delegate_->OnButton(button_id, new_button.pressed, new_button.value);
+    }
+  }
+  if (send_frame)
+    delegate_->OnFrame();
+
+  pad_state_ = new_pad;
+}
+
+std::unique_ptr<device::GamepadDataFetcher>
+Gamepad::GamepadPlatformDataFetcherFactory() {
+  return std::unique_ptr<device::GamepadDataFetcher>(
+      new device::GamepadPlatformDataFetcher());
+}
+
+}  // namespace exo