mus: Implement ScreenMus::GetCursorScreenPoint().

components/mus/ws/user_display_manager.cc

Index: components/mus/ws/user_display_manager.cc
diff --git a/components/mus/ws/user_display_manager.cc b/components/mus/ws/user_display_manager.cc
index e54e9b7fc444c6813b186f2c49f3824770563253..979a5d420501229a35d72a4d5ae7c6119a5be899 100644
--- a/components/mus/ws/user_display_manager.cc
+++ b/components/mus/ws/user_display_manager.cc
@@ -13,7 +13,10 @@ namespace ws {
 
 UserDisplayManager::UserDisplayManager(ws::DisplayManager* display_manager,
                                        const UserId& user_id)
-    : display_manager_(display_manager), user_id_(user_id) {
+    : display_manager_(display_manager),
+      user_id_(user_id),
+      current_cursor_location_(0),
+      cursor_location_memory_(nullptr) {
   for (const WindowManagerState* wms : GetWindowManagerStatesForUser()) {
     if (wms->got_frame_decoration_values()) {
       got_valid_frame_decorations_ = true;
@@ -62,6 +65,54 @@ void UserDisplayManager::OnWillDestroyDisplay(Display* display) {
     test_observer_->OnDisplayRemoved(display->id());
 }
 
+void UserDisplayManager::OnMouseCursorLocationChanged(const gfx::Point& point) {
+  current_cursor_location_ =
+      static_cast<base::subtle::Atomic32>(
+          (point.x() & 0xFFFF) << 16 | (point.y() & 0xFFFF));

[sky, 2016/04/27 23:55:57]

Seems like this loses the sign bit, but again, I could be wrong. How about a
test with a negative x/y?

[Elliot Glaysher, 2016/04/28 00:14:01]

Added unit test to user_display_manager_unittest.cc, which exercises this code.
(I'm not sure how to test the WindowTreeClientImpl code.)

+  if (cursor_location_memory_) {
+    base::subtle::NoBarrier_Store(cursor_location_memory_,
+                                  current_cursor_location_);
+  }
+}
+
+mojo::ScopedSharedBufferHandle UserDisplayManager::GetCursorLocationMemory() {
+  if (!cursor_location_memory_) {
+    // Create our shared memory segment to share the cursor state with our
+    // window clients.
+    MojoResult result = mojo::CreateSharedBuffer(nullptr,
+                                                 sizeof(base::subtle::Atomic32),
+                                                 &cursor_location_handle_);
+    if (result != MOJO_RESULT_OK)
+      return mojo::ScopedSharedBufferHandle();
+    DCHECK(cursor_location_handle_.is_valid());
+
+    result = mojo::MapBuffer(cursor_location_handle_.get(), 0,
+                             sizeof(base::subtle::Atomic32),
+                             reinterpret_cast<void**>(&cursor_location_memory_),
+                             MOJO_MAP_BUFFER_FLAG_NONE);
+    if (result != MOJO_RESULT_OK)
+      return mojo::ScopedSharedBufferHandle();
+    DCHECK(cursor_location_memory_);
+
+    base::subtle::NoBarrier_Store(cursor_location_memory_,
+                                  current_cursor_location_);
+  }
+
+  mojo::ScopedSharedBufferHandle duped;
+  MojoDuplicateBufferHandleOptions options = {
+    sizeof(MojoDuplicateBufferHandleOptions),
+    MOJO_DUPLICATE_BUFFER_HANDLE_OPTIONS_FLAG_READ_ONLY
+  };
+  MojoResult result = mojo::DuplicateBuffer(cursor_location_handle_.get(),
+                                            &options, &duped);
+  if (result != MOJO_RESULT_OK)
+    return mojo::ScopedSharedBufferHandle();
+  DCHECK(duped.is_valid());
+
+  return duped;
+}
+
+
 std::set<const WindowManagerState*>
 UserDisplayManager::GetWindowManagerStatesForUser() const {
   std::set<const WindowManagerState*> result;