Expose Gamepad API instance for Cardboard button

device/vr/android/gvr/cardboard_gamepad_data_provider.h

+// Copyright 2017 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 DEVICE_VR_ANDROID_CARDBOARD_GAMEPAD_DATA_PROVIDER_H
+#define DEVICE_VR_ANDROID_CARDBOARD_GAMEPAD_DATA_PROVIDER_H
+
+#include "device/vr/vr_types.h"
+
+namespace device {
+
+class CardboardGamepadDataFetcher;
+
+// Filled in by vr_shell and consumed by CardboardGamepadDataFetcher.
+struct CardboardGamepadData {
+  int64_t timestamp;
+  bool is_screen_touching;
+};
+
+// This class exposes Cardboard controller (screen touch) data to the gamepad
+// API. Data is reported by VrShell, which implements the
+// CardboardGamepadDataProvider interface.
+//
+// More specifically, here's the lifecycle, assuming VrShell
+// implements GvrGamepadDataProvider:
+//
+// - VrShell creates CardboardGamepadDataFetcherFactory during initialization if
+//  a cardboard is in use, or when WebVR presentation starts.
+//
+// - CardboardGamepadDataFetcherFactory creates CardboardGamepadDataFetcher.
+//
+// - CardboardGamepadDataFetcher registers itself with VrShell via
+//   VrShell::RegisterCardboardGamepadDataFetcher.
+//
+// - While presenting, VrShell::OnTouch calls
+//   CardboardGamepadDataFetcher->SetGamepadData to push button state,
+//   CardboardGamepadDataFetcher::GetGamepadData returns this when polled.
+//
+// - VrShell starts executing its destructor or WebVR presentation ends.
+//
+// - VrShell destructor unregisters CardboardGamepadDataFetcherFactory.
+//
+// - CardboardGamepadDataFetcherFactory destructor destroys
+// CardboardGamepadDataFetcher.
+//
+class CardboardGamepadDataProvider {
+ public:
+  // Called by the gamepad data fetcher constructor to register itself
+  // for receiving data via SetGamepadData. The fetcher must remain
+  // alive while the provider is calling SetGamepadData on it.
+  virtual void RegisterCardboardGamepadDataFetcher(
+      CardboardGamepadDataFetcher*) = 0;
+};
+
+}  // namespace device
+#endif  // DEVICE_VR_ANDROID_CARDBOARD_GAMEPAD_DATA_PROVIDER_H