Emulate Android joystick scroll with synthetic mouse wheel event

content/browser/android/joystick_scroll_provider.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 "content/browser/android/joystick_scroll_provider.h"
+
+#include "base/supports_user_data.h"
+#include "content/browser/renderer_host/input/web_input_event_builders_android.h"
+#include "content/browser/renderer_host/render_widget_host_view_android.h"
+#include "content/browser/web_contents/web_contents_impl.h"
+#include "jni/JoystickScrollProvider_jni.h"
+
+using base::android::AttachCurrentThread;
+using base::android::JavaRef;
+using base::android::ScopedJavaLocalRef;
+
+namespace content {
+
+const void* const kJoystickScrollUserDataKey = &kJoystickScrollUserDataKey;
+
+// A helper class to attach JoystickScrollProvider to the WebContents.
+class JoystickScrollProvider::UserData : public base::SupportsUserData::Data {
+ public:
+  explicit UserData(JoystickScrollProvider* rep) : rep_(rep) {}
+
+ private:
+  std::unique_ptr<JoystickScrollProvider> rep_;
+
+  DISALLOW_IMPLICIT_CONSTRUCTORS(UserData);
+};
+
+jlong Init(JNIEnv* env,
+           const base::android::JavaParamRef<jobject>& obj,
+           const base::android::JavaParamRef<jobject>& jweb_contents) {
+  WebContentsImpl* web_contents = static_cast<WebContentsImpl*>(
+      WebContents::FromJavaWebContents(jweb_contents));
+  CHECK(web_contents)
+      << "A JoystickScrollProvider should be created with a valid WebContents.";
+
+  DCHECK(!web_contents->GetUserData(kJoystickScrollUserDataKey))
+      << "WebContents already has JoystickScrollProvider attached";
+
+  JoystickScrollProvider* native_object =
+      new JoystickScrollProvider(env, obj, web_contents);
+  return reinterpret_cast<intptr_t>(native_object);
+}
+
+JoystickScrollProvider::JoystickScrollProvider(JNIEnv* env,
+                                               const JavaRef<jobject>& obj,
+                                               WebContentsImpl* web_contents)
+    : java_ref_(env, obj), web_contents_(web_contents) {
+  web_contents_->SetUserData(kJoystickScrollUserDataKey, new UserData(this));
+}
+
+JoystickScrollProvider::~JoystickScrollProvider() {
+  JNIEnv* env = AttachCurrentThread();
+  ScopedJavaLocalRef<jobject> j_obj = java_ref_.get(env);
+  java_ref_.reset();
+  if (!j_obj.is_null()) {
+    Java_JoystickScrollProvider_onNativeObjectDestroyed(
+        env, j_obj, reinterpret_cast<intptr_t>(this));
+  }
+}
+
+void JoystickScrollProvider::ScrollBy(
+    JNIEnv* env,
+    const base::android::JavaParamRef<jobject>& obj,
+    jlong time_ms,
+    jfloat dx_dip,
+    jfloat dy_dip) {
+  if (!web_contents_)
+    return;
+
+  RenderWidgetHostViewAndroid* rwhv = static_cast<RenderWidgetHostViewAndroid*>(
+      web_contents_->GetRenderWidgetHostView());
+  if (!rwhv)
+    return;
+
+  if (!dx_dip && !dy_dip)
+    return;
+
+  blink::WebMouseWheelEvent event = WebMouseWheelEventBuilder::Build(
+      dx_dip, dy_dip, 1.0, time_ms / 1000.0, 0, 0);

[boliu, 2016/12/08 06:03:09]

too much implicit casting here, long/float/double, I don't even know what the
compiler is doing

maybe declare 1000.0 as a double constant, or do a static cast

[Tima Vaisburd, 2016/12/08 20:32:19]

Declared MILLISECONDS_IN_SECOND for 1000.0

+
+  rwhv->SendMouseWheelEvent(event);
+}
+
+bool RegisterJoystickScrollProvider(JNIEnv* env) {
+  return RegisterNativesImpl(env);
+}
+
+}  // namespace content