Gamepad API support for chrome on android

content/browser/android/gamepad_reader_impl.cc

+// Copyright 2014 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 "content/browser/android/gamepad_reader_impl.h"
+
+#include "base/android/jni_android.h"
+#include "base/android/jni_string.h"
+#include "base/strings/string_number_conversions.h"
+#include "base/strings/string_util.h"
+#include "base/strings/utf_string_conversions.h"
+
+#include "jni/GamepadList_jni.h"
+
+using base::android::AttachCurrentThread;
+using base::android::CheckException;
+using base::android::ClearException;
+using base::android::ConvertJavaStringToUTF8;
+using base::android::ScopedJavaLocalRef;
+using blink::WebGamepad;
+using blink::WebGamepads;
+
+namespace content {
+
+bool GamepadsReader::RegisterGamepadsReader(JNIEnv* env) {
+  return RegisterNativesImpl(env);
+}
+
+GamepadsReader::GamepadsReader() {
+  JNIEnv* env = AttachCurrentThread();
+  CreateJavaObject(env);
+}
+
+GamepadsReader::~GamepadsReader() { CHECK(java_gamepadList_object_.is_null()); }
+
+GamepadsReader* GamepadsReader::GetInstance() {
+  return Singleton<GamepadsReader>::get();
+}
+
+void GamepadsReader::GetGamepadData(blink::WebGamepads* pads) {
+  JNIEnv* env = AttachCurrentThread();
+  if (!env)
+    return;
+
+  gamepads_data_ = pads;
+  Java_GamepadList_getGamepadData(env, java_gamepadList_object_.obj());
+}
+
+void GamepadsReader::UpdateDeviceCount(JNIEnv* env,
+                                       jobject obj,
+                                       int devicecount) {
+  gamepads_data_->length = devicecount;

[kbalazs, 2014/02/20 00:48:24]

I don't think we need this, other platforms just initialize it to 4 and set the
connected flags appropriately.

+}
+
+void GamepadsReader::SetGamepadData(JNIEnv* env,
+                                    jobject obj,
+                                    int index,
+                                    bool connected,
+                                    jstring devicename,
+                                    int64 timestamp,
+                                    jfloatArray jaxes,
+                                    jfloatArray jbuttons) {
+
+  blink::WebGamepad& pad = gamepads_data_->items[index];
+  pad.connected = connected;
+
+  pad.timestamp = timestamp;
+
+  // Do not set gamepad parameters for all the gamepad devices that are not
+  // attached.
+  if (!connected)
+    return;
+
+  // Map the Gamepad DeviceName String to the WebGamepad Id and then convert
+  // the utf-8 id string to WebUChar. Ideally it should be mapped to vendor and
+  // product information but it is only available at kernel level and it can
+  // not be queried using class android.hardware.input.InputManager.
+
+  std::string device_name =
+      base::android::ConvertJavaStringToUTF8(env, devicename);
+  base::TruncateUTF8ToByteSize(
+      device_name, blink::WebGamepad::idLengthCap - 1, &device_name);
+  base::string16 tmp16 = base::UTF8ToUTF16(device_name);

[kbalazs, 2014/02/20 00:48:24]

Can we get rid of converting back and forth (utf16->utf8->utf16)? Both WebUChar
and jchar is 2 byte so I think it's better to just memcpy the java string to to
pad.id.

+  memset(pad.id, 0, sizeof(pad.id));
+  tmp16.copy(pad.id, arraysize(pad.id) - 1);
+
+  pad.timestamp = timestamp;
+
+  // Set WebGamepad axeslength to total number of axes on the gamepad device.
+  // Only return the first axesLengthCap if axeslength captured by GamepadList
+  // is larger than axesLengthCap.
+
+  std::vector<float> axes;
+  base::android::JavaFloatArrayToFloatVector(env, jaxes, &axes);
+  pad.axesLength = (axes.size() > WebGamepad::axesLengthCap)
+                       ? WebGamepad::axesLengthCap
+                       : axes.size();
+
+  // Copy axes state to the WebGamepad axes[].
+  for (unsigned int j = 0; j < pad.axesLength; j++)

[kbalazs, 2014/02/20 00:48:24]

This can also be done with only one copy instead of two. I would use the jni
api's directly to grab the data and memcpy it. Of course one can argue that this
is more error prone, but in my opinion it's worth it.

+    pad.axes[j] = axes[j];
+
+  // Set WebGamepad buttonslength to total number of axes on the gamepad
+  // device. Only return the first buttonsLengthCap if axeslength captured by
+  // GamepadList is larger than buttonsLengthCap.
+
+  std::vector<float> buttons;
+  base::android::JavaFloatArrayToFloatVector(env, jbuttons, &buttons);

[kbalazs, 2014/02/20 00:48:24]

Ditto.

+  pad.buttonsLength = (buttons.size() > WebGamepad::buttonsLengthCap)
+                          ? WebGamepad::buttonsLengthCap
+                          : buttons.size();
+
+  // Copy buttons state to the WebGamepad buttons[].
+  for (unsigned int j = 0; j < pad.buttonsLength; j++)
+    pad.buttons[j] = buttons[j];
+}
+
+void GamepadsReader::NotifyForGamepadsAccess(bool isaccesspaused) {

[kbalazs, 2014/02/20 00:48:24]

is_access_paused? Or just access_paused?

+  JNIEnv* env = AttachCurrentThread();
+  if (!env)
+    return;
+
+  CHECK(!java_gamepadList_object_.is_null());
+  Java_GamepadList_notifyForGamepadsAccess(
+      env, java_gamepadList_object_.obj(), isaccesspaused);
+}
+
+void GamepadsReader::CreateJavaObject(JNIEnv* env) {
+  // Create the Java GamepadsReader object and attach it with GamepadList
+  // object.
+  java_gamepadList_object_.Reset(
+      Java_GamepadList_getInstance(env, reinterpret_cast<intptr_t>(this)));
+  CHECK(!java_gamepadList_object_.is_null());
+}
+
+}  // namespace content