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 "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 "device/gamepad/gamepad_data_fetcher.h"
+#include "device/gamepad/gamepad_platform_data_fetcher.h"
+
+namespace exo {
+
+namespace {

[reveman, 2016/06/29 21:55:44]

nit: blank line after this. blank line before is not needed

[denniskempin, 2016/06/30 00:29:21]

Done.

+constexpr double kEpsilon = 0.001;

[reveman, 2016/06/29 21:55:44]

nit: kGamepadButtonValueEpsilon and blank line after this line

[denniskempin, 2016/06/30 00:29:21]

Done.

+bool almostEquals(double a, double b) {

[reveman, 2016/06/29 21:55:44]

GamepadButtonValuesAreEqual()?

[denniskempin, 2016/06/30 00:29:21]

Done.

+  return fabs(a - b) < kEpsilon;
+}
+
+}  // anonymous namespace

[reveman, 2016/06/29 21:55:44]

nit: "}  // namespace" to be consistent with rest of exo/

[denniskempin, 2016/06/30 00:29:21]

Done.

+
+////////////////////////////////////////////////////////////////////////////////
+// Gamepad, public:
+
+Gamepad::Gamepad(size_t id, GamepadDelegate* delegate)
+    : Gamepad(id, delegate, nullptr) {}
+
+Gamepad::Gamepad(size_t id,
+                 GamepadDelegate* delegate,
+                 std::unique_ptr<device::GamepadDataFetcher> fetcher)
+    : id_(id),
+      delegate_(delegate),
+      fetcher_(std::move(fetcher)),
+      polling_thread_(new base::Thread("Exo gamepad polling thread")),
+      origin_task_runner_(base::ThreadTaskRunnerHandle::Get()) {
+  polling_thread_->StartWithOptions(
+      base::Thread::Options(base::MessageLoop::TYPE_IO, 0));
+  polling_thread_->task_runner()->PostTask(
+      FROM_HERE,
+      base::Bind(&Gamepad::InitializePollingThread, base::Unretained(this)));
+}
+
+Gamepad::~Gamepad() {
+  delegate_->OnGamepadDestroying(this);
+  polling_thread_->Stop();
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Gamepad, private:
+
+void Gamepad::ScheduleOnPoll() {
+  polling_thread_->task_runner()->PostDelayedTask(
+      FROM_HERE, base::Bind(&Gamepad::OnPoll, base::Unretained(this)),
+      base::TimeDelta::FromMilliseconds(16));

[reveman, 2016/06/29 21:55:44]

16? Please add a constant and a comment for this magic value

[denniskempin, 2016/06/30 00:29:21]

Done.

+}
+
+void Gamepad::InitializePollingThread() {
+  DCHECK(base::MessageLoop::current() == polling_thread_->message_loop());
+  // The platform data fetcher has to be initialized on the polling thread.
+  if (!fetcher_)
+    fetcher_.reset(new device::GamepadPlatformDataFetcher());
+  ScheduleOnPoll();
+}
+
+void Gamepad::OnPoll() {
+  DCHECK(base::MessageLoop::current() == polling_thread_->message_loop());
+  DCHECK(fetcher_);
+
+  // Update state with data from gamepad data fetcher

[reveman, 2016/06/29 21:55:44]

s/fetcher/fetcher./

[denniskempin, 2016/06/30 00:29:21]

Done.

+  blink::WebGamepads new_state = state_;
+  fetcher_->GetGamepadData(&new_state, false);
+  PostGamepadChanges(new_state);
+
+  state_ = new_state;
+  ScheduleOnPoll();
+}
+
+void Gamepad::PostGamepadChanges(const blink::WebGamepads new_state) {
+  DCHECK(base::MessageLoop::current() == polling_thread_->message_loop());

[reveman, 2016/06/29 21:55:44]

Can you use the thread checker here instead?

[denniskempin, 2016/06/30 00:29:21]

It's a different thread. This runs in the polling thread. The thread checker
checks for the origin thread. 

+
+  if (id_ >= std::max(new_state.length, state_.length))
+    return;
+
+  bool send_frame = false;
+  const blink::WebGamepad& new_pad = new_state.items[id_];
+  blink::WebGamepad& pad = state_.items[id_];
+
+  // Update connection state

[reveman, 2016/06/29 21:55:44]

nit: s/state/state./

[denniskempin, 2016/06/30 00:29:21]

Done.

+  if (new_pad.connected != pad.connected) {
+    origin_task_runner_->PostTask(
+        FROM_HERE, base::Bind(&GamepadDelegate::OnStateChange,
+                              base::Unretained(delegate_), new_pad.connected));

[reveman, 2016/06/29 21:55:44]

Is base::Unretained safe here and below? what if the gamepad is destroyed before
this is processed?

+  }
+
+  if (!new_pad.connected || new_pad.timestamp <= pad.timestamp)
+    return;
+
+  // Notify delegate of updated axes

[reveman, 2016/06/29 21:55:44]

nit: s/axes/axes./

[denniskempin, 2016/06/30 00:29:21]

Done.

+  for (size_t axis = 0; axis < std::max(pad.axesLength, new_pad.axesLength);
+       ++axis) {
+    if (!almostEquals(new_pad.axes[axis], pad.axes[axis])) {
+      send_frame = true;
+      origin_task_runner_->PostTask(
+          FROM_HERE,
+          base::Bind(&GamepadDelegate::OnAxis, base::Unretained(delegate_),
+                     axis, new_pad.axes[axis]));
+    }
+  }
+
+  // Notify delegate of updated buttons

[reveman, 2016/06/29 21:55:44]

nit: s/buttons/buttons./

[denniskempin, 2016/06/30 00:29:21]

Done.

+  for (size_t button = 0;
+       button < std::max(pad.buttonsLength, new_pad.buttonsLength); ++button) {
+    if (!almostEquals(new_pad.buttons[button].value,
+                      pad.buttons[button].value) ||
+        pad.buttons[button].pressed != new_pad.buttons[button].pressed) {

[reveman, 2016/06/29 21:55:44]

check "pressed" first as it's cheaper

[denniskempin, 2016/06/30 00:29:21]

Done.

+      send_frame = true;
+      origin_task_runner_->PostTask(
+          FROM_HERE,
+          base::Bind(&GamepadDelegate::OnButton, base::Unretained(delegate_),
+                     button, new_pad.buttons[button].pressed,
+                     new_pad.buttons[button].value));
+    }
+  }
+  if (send_frame) {
+    origin_task_runner_->PostTask(
+        FROM_HERE,
+        base::Bind(&GamepadDelegate::OnFrame, base::Unretained(delegate_)));
+  }
+}
+
+}  // namespace exo