Refactoring gamepad polling to support dynamically added sources

content/browser/gamepad/gamepad_provider.cc

Index: content/browser/gamepad/gamepad_provider.cc
diff --git a/content/browser/gamepad/gamepad_provider.cc b/content/browser/gamepad/gamepad_provider.cc
index 682afc51d353a73cc0759ec433c5f9e7ecae1772..430af56de642becf1a063d751ab8917f0e352a59 100644
--- a/content/browser/gamepad/gamepad_provider.cc
+++ b/content/browser/gamepad/gamepad_provider.cc
@@ -7,7 +7,6 @@
 #include <stddef.h>
 #include <string.h>
 #include <cmath>
-#include <set>
 #include <utility>
 #include <vector>
 
@@ -31,6 +30,12 @@
 using blink::WebGamepad;
 using blink::WebGamepads;
 
+namespace {
+
+const float kMinAxisResetValue = 0.1f;
+
+} // namespace
+
 namespace content {
 
 GamepadProvider::ClosureAndThread::ClosureAndThread(
@@ -46,7 +51,8 @@ GamepadProvider::GamepadProvider()
     : is_paused_(true),
       have_scheduled_do_poll_(false),
       devices_changed_(true),
-      ever_had_user_gesture_(false) {
+      ever_had_user_gesture_(false),
+      sanitize_(true) {
   Initialize(scoped_ptr<GamepadDataFetcher>());
 }
 
@@ -66,7 +72,6 @@ GamepadProvider::~GamepadProvider() {
   // Use Stop() to join the polling thread, as there may be pending callbacks
   // which dereference |polling_thread_|.
   polling_thread_->Stop();
-  data_fetcher_.reset();
 }
 
 base::SharedMemoryHandle GamepadProvider::GetSharedMemoryHandleForProcess(
@@ -132,6 +137,9 @@ void GamepadProvider::Initialize(scoped_ptr<GamepadDataFetcher> fetcher) {
   memset(hwbuf, 0, sizeof(GamepadHardwareBuffer));
   pad_states_.reset(new PadState[WebGamepads::itemsLengthCap]);
 
+  for (unsigned i = 0; i < WebGamepads::itemsLengthCap; ++i)
+    ClearPadState(pad_states_.get()[i]);
+
   polling_thread_.reset(new base::Thread("Gamepad polling thread"));
 #if defined(OS_LINUX)
   // On Linux, the data fetcher needs to watch file descriptors, so the message
@@ -149,59 +157,34 @@ void GamepadProvider::Initialize(scoped_ptr<GamepadDataFetcher> fetcher) {
 #endif
   polling_thread_->StartWithOptions(base::Thread::Options(kMessageLoopType, 0));
 
+  if (fetcher) {
+    AddGamepadDataFetcher(std::move(fetcher));
+  } else {
+    AddGamepadPlatformDataFetchers(this);
+  }
+}
+
+void GamepadProvider::AddGamepadDataFetcher(
+    scoped_ptr<GamepadDataFetcher> fetcher) {
   polling_thread_->task_runner()->PostTask(
-      FROM_HERE, base::Bind(&GamepadProvider::DoInitializePollingThread,
+      FROM_HERE, base::Bind(&GamepadProvider::DoAddGamepadDataFetcher,
                             base::Unretained(this), base::Passed(&fetcher)));
 }
 
-void GamepadProvider::DoInitializePollingThread(
+void GamepadProvider::DoAddGamepadDataFetcher(
     scoped_ptr<GamepadDataFetcher> fetcher) {
   DCHECK(base::MessageLoop::current() == polling_thread_->message_loop());
-  DCHECK(!data_fetcher_.get());  // Should only initialize once.
 
-  if (!fetcher)
-    fetcher.reset(new GamepadPlatformDataFetcher);
-  data_fetcher_ = std::move(fetcher);
+  fetcher->InitializeProvider(this);
+
+  data_fetchers_.push_back(std::move(fetcher));
 }
 
 void GamepadProvider::SendPauseHint(bool paused) {
   DCHECK(base::MessageLoop::current() == polling_thread_->message_loop());
-  if (data_fetcher_)
-    data_fetcher_->PauseHint(paused);
-}
-
-bool GamepadProvider::PadState::Match(const WebGamepad& pad) const {
-  return connected_ == pad.connected &&
-         axes_length_ == pad.axesLength &&
-         buttons_length_ == pad.buttonsLength &&
-         memcmp(id_, pad.id, sizeof(id_)) == 0 &&
-         memcmp(mapping_, pad.mapping, sizeof(mapping_)) == 0;
-}
-
-void GamepadProvider::PadState::SetPad(const WebGamepad& pad) {
-  connected_ = pad.connected;
-  axes_length_ = pad.axesLength;
-  buttons_length_ = pad.buttonsLength;
-  memcpy(id_, pad.id, sizeof(id_));
-  memcpy(mapping_, pad.mapping, sizeof(mapping_));
-}
-
-void GamepadProvider::PadState::SetDisconnected() {
-  connected_ = false;
-  axes_length_ = 0;
-  buttons_length_ = 0;
-  memset(id_, 0, sizeof(id_));
-  memset(mapping_, 0, sizeof(mapping_));
-}
-
-void GamepadProvider::PadState::AsWebGamepad(WebGamepad* pad) {
-  pad->connected = connected_;
-  pad->axesLength = axes_length_;
-  pad->buttonsLength = buttons_length_;
-  memcpy(pad->id, id_, sizeof(id_));
-  memcpy(pad->mapping, mapping_, sizeof(mapping_));
-  memset(pad->axes, 0, sizeof(pad->axes));
-  memset(pad->buttons, 0, sizeof(pad->buttons));
+  for (const auto& it : data_fetchers_) {
+    it->PauseHint(paused);
+  }
 }
 
 void GamepadProvider::DoPoll() {
@@ -223,29 +206,52 @@ void GamepadProvider::DoPoll() {
     devices_changed_ = false;
   }
 
+  // Loop through each registered data fetcher and poll its gamepad data.
+  // It's expected that GetGamepadData will mark each gamepad as active (via
+  // GetPadState). If a gamepad is not marked as active during the calls to
+  // GetGamepadData then it's assumed to be disconnected.
+  for (const auto& it : data_fetchers_) {
+    it->GetGamepadData(changed);
+  }
+
+  // Send out disconnect events using the last polled data before we wipe it out
+  // in the mapping step.
+  if (ever_had_user_gesture_) {
+    for (unsigned i = 0; i < WebGamepads::itemsLengthCap; ++i) {
+      PadState& state = pad_states_.get()[i];
+
+      if (!state.active_state && state.source != GAMEPAD_SOURCE_NONE) {
+        OnGamepadConnectionChange(false, i, hwbuf->buffer.items[i]);
+        ClearPadState(state);
+      }
+    }
+  }
+
   {
     base::AutoLock lock(shared_memory_lock_);
 
     // Acquire the SeqLock. There is only ever one writer to this data.
     // See gamepad_hardware_buffer.h.
     hwbuf->sequence.WriteBegin();
-    data_fetcher_->GetGamepadData(&hwbuf->buffer, changed);
+    hwbuf->buffer.length = 0;
+    for (unsigned i = 0; i < WebGamepads::itemsLengthCap; ++i) {
+      PadState& state = pad_states_.get()[i];
+      // Must run through the map+sanitize here or CheckForUserGesture may fail.
+      MapAndSanitizeGamepadData(&state, &hwbuf->buffer.items[i]);
+      if (state.active_state)
+        hwbuf->buffer.length++;
+    }
     hwbuf->sequence.WriteEnd();
   }
 
   if (ever_had_user_gesture_) {
     for (unsigned i = 0; i < WebGamepads::itemsLengthCap; ++i) {
-      WebGamepad& pad = hwbuf->buffer.items[i];
       PadState& state = pad_states_.get()[i];
-      if (pad.connected && !state.connected()) {
-        OnGamepadConnectionChange(true, i, pad);
-      } else if (!pad.connected && state.connected()) {
-        OnGamepadConnectionChange(false, i, pad);
-      } else if (pad.connected && state.connected() && !state.Match(pad)) {
-        WebGamepad old_pad;
-        state.AsWebGamepad(&old_pad);
-        OnGamepadConnectionChange(false, i, old_pad);
-        OnGamepadConnectionChange(true, i, pad);
+
+      if (state.active_state) {
+        if (state.active_state == GAMEPAD_NEWLY_ACTIVE)
+          OnGamepadConnectionChange(true, i, hwbuf->buffer.items[i]);
+        state.active_state = GAMEPAD_INACTIVE;
       }
     }
   }
@@ -275,12 +281,6 @@ void GamepadProvider::ScheduleDoPoll() {
 
 void GamepadProvider::OnGamepadConnectionChange(
     bool connected, int index, const WebGamepad& pad) {
-  PadState& state = pad_states_.get()[index];
-  if (connected)
-    state.SetPad(pad);
-  else
-    state.SetDisconnected();
-
   BrowserThread::PostTask(
       BrowserThread::IO,
       FROM_HERE,
@@ -310,7 +310,6 @@ void GamepadProvider::CheckForUserGesture() {
   if (user_gesture_observers_.empty() && ever_had_user_gesture_)
     return;
 
-  bool had_gesture_before = ever_had_user_gesture_;
   const WebGamepads& pads = SharedMemoryAsHardwareBuffer()->buffer;
   if (GamepadsHaveUserGesture(pads)) {
     ever_had_user_gesture_ = true;
@@ -320,10 +319,92 @@ void GamepadProvider::CheckForUserGesture() {
     }
     user_gesture_observers_.clear();
   }
-  if (!had_gesture_before && ever_had_user_gesture_) {
-    // Initialize pad_states_ for the first time.
-    for (size_t i = 0; i < WebGamepads::itemsLengthCap; ++i) {
-      pad_states_.get()[i].SetPad(pads.items[i]);
+}
+
+void GamepadProvider::ClearPadState(PadState& state) {
+  memset(&state, 0, sizeof(PadState));
+}
+
+PadState* GamepadProvider::GetPadState(GamepadSource source, int source_id) {
+  // Check to see if the device already has a reserved slot
+  PadState* empty_slot = nullptr;
+  for (size_t i = 0; i < WebGamepads::itemsLengthCap; ++i) {
+    PadState& state = pad_states_.get()[i];
+    if (state.source == source &&
+        state.source_id == source_id) {
+      // Retrieving the pad state marks this gamepad as active.
+      state.active_state = GAMEPAD_ACTIVE;
+      return &state;
+    }
+    if (!empty_slot && state.source == GAMEPAD_SOURCE_NONE)
+      empty_slot = &state;
+  }
+  if (empty_slot) {
+    empty_slot->source = source;
+    empty_slot->source_id = source_id;
+    empty_slot->active_state = GAMEPAD_NEWLY_ACTIVE;
+  }
+  return empty_slot;
+}
+
+void GamepadProvider::MapAndSanitizeGamepadData(
+    PadState* pad_state, WebGamepad* pad) {
+  DCHECK(pad_state);
+  DCHECK(pad);
+
+  if (!pad_state->active_state) {
+    memset(pad, 0, sizeof(WebGamepad));
+    return;
+  }
+
+  // Copy the current state to the output buffer, using the mapping
+  // function, if there is one available.
+  if (pad_state->mapper)
+    pad_state->mapper(pad_state->data, pad);
+  else
+    *pad = pad_state->data;
+
+  pad->connected = true;
+
+  if (!sanitize_)
+    return;
+
+  // About sanitization: Gamepads may report input event if the user is not
+  // interacting with it, due to hardware problems or environmental ones (pad
+  // has something heavy leaning against an axis.) This may cause user gestures
+  // to be detected erroniously, exposing gamepad information when the user had
+  // no intention of doing so. To avoid this we require that each button or axis
+  // report being at rest (zero) at least once before exposing its value to the
+  // Gamepad API. This state is tracked by the axis_mask and button_mask
+  // bitfields. If the bit for an axis or button is 0 it means the axis has
+  // never reported being at rest, and the value will be forced to zero.
+
+  // We can skip axis sanitation if all available axes have been masked.
+  uint32_t full_axis_mask = (1 << pad->axesLength) - 1;
+  if (pad_state->axis_mask != full_axis_mask) {
+    for (size_t axis = 0; axis < pad->axesLength; ++axis) {
+      if (!(pad_state->axis_mask & 1 << axis)) {
+        if (fabs(pad->axes[axis]) < kMinAxisResetValue) {
+          pad_state->axis_mask |= 1 << axis;
+        } else {
+          pad->axes[axis] = 0.0f;
+        }
+      }
+    }
+  }
+
+  // We can skip button sanitation if all available buttons have been masked.
+  uint32_t full_button_mask = (1 << pad->buttonsLength) - 1;
+  if (pad_state->button_mask != full_button_mask) {
+    for (size_t button = 0; button < pad->buttonsLength; ++button) {
+      if (!(pad_state->button_mask & 1 << button)) {
+        if (!pad->buttons[button].pressed) {
+          pad_state->button_mask |= 1 << button;
+        } else {
+          pad->buttons[button].pressed = false;
+          pad->buttons[button].value = 0.0f;
+        }
+      }
     }
   }
 }