mus: Implement interwindow drag and drop

services/ui/ws/drag_controller.cc

Index: services/ui/ws/drag_controller.cc
diff --git a/services/ui/ws/drag_controller.cc b/services/ui/ws/drag_controller.cc
new file mode 100644
index 0000000000000000000000000000000000000000..97f3053521ea8198209c563b79651e189f19c553
--- /dev/null
+++ b/services/ui/ws/drag_controller.cc
@@ -0,0 +1,287 @@
+// 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 "services/ui/ws/drag_controller.h"
+
+#include "base/logging.h"
+#include "services/ui/ws/drag_source.h"
+#include "services/ui/ws/drag_target_connection.h"
+#include "services/ui/ws/event_dispatcher.h"
+#include "services/ui/ws/server_window.h"
+
+namespace ui {
+namespace ws {
+
+struct DragController::Operation {
+  OperationType type;
+  uint32_t event_flags;
+  gfx::Point screen_position;
+};
+
+struct DragController::WindowState {

[sky, 2016/09/15 18:10:47]

Much easier to understand, and better documented. Thanks!

+  // Set to true once we've observed

[sky, 2016/09/15 18:10:47]

Did you forget to finish the sentence?

+  bool observed;
+
+  // If we're waiting for a response, this is the type of message. TYPE_NONE
+  // means there's no outstanding
+  OperationType waiting_on_reply;
+
+  // The operation that we'll send off if |waiting_on_reply| isn't TYPE_NONE.
+  Operation queued_operation;
+};
+
+DragController::DragController(
+    DragSource* source,
+    ServerWindow* source_window,
+    DragTargetConnection* source_connection,
+    int32_t drag_pointer,
+    mojo::Map<mojo::String, mojo::Array<uint8_t>> mime_data,
+    uint32_t drag_operations)
+    : source_(source),
+      drag_operations_(drag_operations),
+      drag_pointer_id_(drag_pointer),
+      source_window_(source_window),
+      source_connection_(source_connection),
+      mime_data_(std::move(mime_data)),
+      weak_factory_(this) {
+  EnsureWindowObserved(source_window_);
+}
+
+DragController::~DragController() {
+  for (auto& pair : window_state_) {
+    if (pair.second.observed)
+      pair.first->RemoveObserver(this);
+  }
+}
+
+void DragController::Cancel() {
+  MessageDragCompleted(false);
+  // |this| may be deleted now.
+}
+
+bool DragController::DispatchPointerEvent(const ui::PointerEvent& event,
+                                          ServerWindow* current_target) {
+  uint32_t event_flags =
+      event.flags() &
+      (ui::EF_SHIFT_DOWN | ui::EF_CONTROL_DOWN | ui::EF_ALT_DOWN);
+  gfx::Point screen_position = event.location();
+
+  if (waiting_for_final_drop_response_) {
+    // If we're waiting on a target window to respond to the final drag drop
+    // call, don't process any more pointer events.
+    return false;
+  }
+
+  if (event.pointer_id() != drag_pointer_id_)
+    return false;
+
+  // If |current_target| doesn't accept drags, walk its hierarchy up until we
+  // find one that does (or set to nullptr at the top of the tree).
+  while (current_target && !current_target->can_accept_drops())
+    current_target = current_target->parent();
+
+  if (current_target) {
+    // If we're non-null, we're about to use |current_target| in some
+    // way. Ensure that we receive notifications that this window has gone
+    // away.
+    EnsureWindowObserved(current_target);
+  }
+
+  if (current_target && current_target == current_target_window_ &&
+      event.type() != ET_POINTER_UP) {
+    QueueOperation(current_target, OperationType::OVER, event_flags,
+                   screen_position);
+  } else if (current_target != current_target_window_) {
+    if (current_target_window_) {
+      QueueOperation(current_target_window_, OperationType::LEAVE, event_flags,
+                     screen_position);
+    }
+
+    if (current_target) {
+      // TODO(erg): If we have a queued LEAVE operation, does this turn into a
+      // noop?
+      QueueOperation(current_target, OperationType::ENTER, event_flags,
+                     screen_position);
+    }
+
+    SetCurrentTargetWindow(current_target);
+  }
+
+  if (event.type() == ET_POINTER_UP) {
+    if (current_target) {
+      QueueOperation(current_target, OperationType::DROP, event_flags,
+                     screen_position);
+      waiting_for_final_drop_response_ = true;
+    } else {
+      // The pointer was released over no window or a window that doesn't
+      // accept drags.
+      MessageDragCompleted(false);
+    }
+  }
+
+  return true;
+}
+
+void DragController::OnWillDestroyDragTargetConnection(
+    DragTargetConnection* connection) {
+  called_on_drag_mime_types_.erase(connection);
+}
+
+void DragController::MessageDragCompleted(bool success) {
+  for (DragTargetConnection* connection : called_on_drag_mime_types_)
+    connection->PerformOnDragDropDone();
+  called_on_drag_mime_types_.clear();
+
+  source_->OnDragCompleted(success);
+  // |this| may be deleted now.
+}
+
+size_t DragController::GetSizeOfQueueForWindow(ServerWindow* window) {

[sky, 2016/09/15 18:10:47]

It doesn't seem as though you are using this anymore?

[Elliot Glaysher, 2016/09/15 19:14:33]

It's used in the unit tests via the private testing api.

+  auto it = window_state_.find(window);
+  if (it == window_state_.end())
+    return 0u;
+  if (it->second.waiting_on_reply == OperationType::NONE)
+    return 0u;
+  if (it->second.queued_operation.type == OperationType::NONE)
+    return 1u;
+  return 2u;
+}
+
+void DragController::SetCurrentTargetWindow(ServerWindow* current_target) {
+  current_target_window_ = current_target;
+}
+
+void DragController::EnsureWindowObserved(ServerWindow* window) {
+  if (!window)
+    return;
+
+  WindowState& state = window_state_[window];
+  if (!state.observed) {
+    state.observed = true;
+    window->AddObserver(this);
+  }
+}
+
+void DragController::QueueOperation(ServerWindow* window,
+                                    OperationType type,
+                                    uint32_t event_flags,
+                                    gfx::Point screen_position) {
+  // If this window doesn't have the mime data, send it.
+  DragTargetConnection* connection = source_->GetDragTargetForWindow(window);
+  if (connection != source_connection_ &&
+      !base::ContainsKey(called_on_drag_mime_types_, connection)) {
+    connection->PerformOnDragDropStart(mime_data_.Clone());
+    called_on_drag_mime_types_.insert(connection);
+  }
+
+  WindowState& state = window_state_[window];
+  // Set the queued operation to the incoming.
+  state.queued_operation = {type, event_flags, screen_position};
+
+  if (state.waiting_on_reply == OperationType::NONE) {
+    // Send the operation immediately.
+    DispatchOperation(window, &state);
+  }
+}
+
+void DragController::DispatchOperation(ServerWindow* target,
+                                       WindowState* state) {
+  DragTargetConnection* connection = source_->GetDragTargetForWindow(target);
+
+  DCHECK_EQ(OperationType::NONE, state->waiting_on_reply);
+  Operation& op = state->queued_operation;
+  switch (op.type) {
+    case OperationType::NONE: {

[sky, 2016/09/15 18:10:47]

It is possible to get here with an operation of NONE? Assuming it is, please
document why as it isn't readily obvious how you end up here with a type of
NONE.

[Elliot Glaysher, 2016/09/15 19:14:33]

Added a NOTREACHED() to emphasize that this is to silence the compiler.

+      break;
+    }
+    case OperationType::ENTER: {
+      connection->PerformOnDragEnter(
+          target, op.event_flags, op.screen_position, drag_operations_,
+          base::Bind(&DragController::OnDragStatusCompleted,
+                     weak_factory_.GetWeakPtr(), target->id()));
+      state->waiting_on_reply = OperationType::ENTER;
+      break;
+    }
+    case OperationType::OVER: {
+      connection->PerformOnDragOver(
+          target, op.event_flags, op.screen_position, drag_operations_,
+          base::Bind(&DragController::OnDragStatusCompleted,
+                     weak_factory_.GetWeakPtr(), target->id()));
+      state->waiting_on_reply = OperationType::OVER;
+      break;
+    }
+    case OperationType::LEAVE: {
+      connection->PerformOnDragLeave(target);
+      state->waiting_on_reply = OperationType::NONE;
+      break;
+    }
+    case OperationType::DROP: {
+      connection->PerformOnCompleteDrop(
+          target, op.event_flags, op.screen_position, drag_operations_,
+          base::Bind(&DragController::OnDragDropCompleted,
+                     weak_factory_.GetWeakPtr(), target->id()));
+      state->waiting_on_reply = OperationType::DROP;
+      break;
+    }
+  }
+
+  state->queued_operation = {OperationType::NONE, 0, gfx::Point()};
+}
+
+void DragController::OnRespondToOperation(ServerWindow* window) {
+  WindowState& state = window_state_[window];
+  DCHECK_NE(OperationType::NONE, state.waiting_on_reply);
+  state.waiting_on_reply = OperationType::NONE;
+  if (state.queued_operation.type != OperationType::NONE)
+    DispatchOperation(window, &state);
+}
+
+void DragController::OnDragStatusCompleted(const WindowId& id,
+                                           uint32_t bitmask) {
+  ServerWindow* window = source_->GetWindowById(id);
+  if (!window) {
+    // The window has been deleted and its queue is empty.
+    return;
+  }
+
+  // We must remove the completed item.
+  OnRespondToOperation(window);
+
+  // TODO(erg): |bitmask| is the allowed drag actions at the mouse location. We
+  // should use this data to change the cursor.
+}
+
+void DragController::OnDragDropCompleted(const WindowId& id, uint32_t bitmask) {
+  ServerWindow* window = source_->GetWindowById(id);
+  if (!window) {
+    // The window has been deleted after we sent the drop message. It's really
+    // hard to recover from this so just signal to the source that our drag
+    // failed.
+    MessageDragCompleted(false);
+    return;
+  }
+
+  OnRespondToOperation(window);
+  MessageDragCompleted(bitmask != 0u);
+}
+
+void DragController::OnWindowDestroying(ServerWindow* window) {
+  auto it = window_state_.find(window);
+  if (it != window_state_.end()) {
+    window->RemoveObserver(this);
+    window_state_.erase(it);
+  }
+
+  if (current_target_window_ == window)
+    current_target_window_ = nullptr;
+
+  if (source_window_ == window) {
+    source_window_ = nullptr;
+    // Our source window is being deleted, fail the drag.
+    MessageDragCompleted(false);
+  }
+}
+
+}  // namespace ws
+}  // namespace ui