Implement workspace scrubbing

ash/wm/workspace/workspace_cycler.cc

+// Copyright (c) 2012 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 "ash/wm/workspace/workspace_cycler.h"
+
+#include "ash/shell.h"
+#include "ash/wm/workspace/workspace_manager.h"
+#include "ui/aura/window.h"
+#include "ui/base/events/event.h"
+
+namespace ash {
+namespace internal {
+
+namespace {
+
+// The required vertical distance to scrub to the next workspace.
+const int kWorkspaceStepSize = 50;
+
+// The maximum horizontal movement in between switching between two workspaces
+// before the workspace scrubbing session is cancelled.
+const int kMaxHorizontalMovementPerWorkspaceStep = 50;
+
+// Returns true is scrubbing is enabled.
+bool IsScrubbingEnabled() {
+  // Scrubbing is disabled if the screen is locked or a modal dialog is open.
+  return !Shell::GetInstance()->IsScreenLocked() &&
+         !Shell::GetInstance()->IsSystemModalWindowOpen();
+}
+
+}  // namespace
+
+WorkspaceCycler::WorkspaceCycler(WorkspaceManager* workspace_manager)
+    : workspace_manager_(workspace_manager),
+      scrub_state_(NOT_SCRUBBING),
+      initial_workspace_window_(NULL) {
+  ash::Shell::GetInstance()->AddPreTargetHandler(this);
+}
+
+WorkspaceCycler::~WorkspaceCycler() {
+  if (scrub_state_ != NOT_SCRUBBING)
+    StopScrubbing();
+  ash::Shell::GetInstance()->RemovePreTargetHandler(this);
+}
+
+void WorkspaceCycler::StartScrubbing() {
+  scrub_state_ = SCRUBBING;
+  initial_workspace_window_ = workspace_manager_->GetActiveWorkspaceWindow();
+  DCHECK(initial_workspace_window_->IsVisible());
+  initial_workspace_window_->AddObserver(this);
+}
+
+void WorkspaceCycler::StopScrubbing() {
+  if (initial_workspace_window_)
+    initial_workspace_window_->RemoveObserver(this);
+  initial_workspace_window_ = NULL;
+
+  scrub_state_ = NOT_SCRUBBING;
+}
+
+void WorkspaceCycler::OnWindowDestroyed(aura::Window* window) {
+  DCHECK_EQ(window, initial_workspace_window_);
+  window->RemoveObserver(this);
+
+  // |initial_workspace_window_| may be destroyed while scrubbing is active
+  // if the user closes or unmaximizes windows via the keyboard in the
+  // workspace corresponding to |initial_workspace_window_|.
+  initial_workspace_window_ = NULL;
+  scrub_state_ = CANCELLED_SCRUBBING;
+}
+
+ui::EventResult WorkspaceCycler::OnMouseEvent(ui::MouseEvent* event) {
+  if (!IsScrubbingEnabled())
+    return ui::ER_UNHANDLED;
+
+  if (!(event->type() == ui::ET_MOUSE_PRESSED ||
+      event->type() == ui::ET_MOUSE_DRAGGED ||
+      event->type() == ui::ET_MOUSE_RELEASED)) {

[sky, 2012/11/28 15:15:34]

nit: indent to match previous line.
Also, this could is more readable if you carry through the !, eg event->type()
!= DRAGGED && type != PRESSED..
And what about capture changed, shouldn't that cancel scrubbing?
This code seems like it would be easier to follow if you based it off the
current scrub_state_ first, but maybe I'm wrong.

[pkotwicz, 2012/11/29 01:01:46]

Fixed nit. Added comment to explain behavior.
We don't want to cancel scrubbing if we get a different mouse event because we
don't want to cancel scrubbing upon getting ui::ET_MOUSE_ENTERED

+    return ui::ER_UNHANDLED;
+  }
+
+  if (event->type() == ui::ET_MOUSE_RELEASED ||
+      !(event->flags() & ui::EF_CONTROL_DOWN) ||
+      !(event->flags() & ui::EF_LEFT_MOUSE_BUTTON)) {
+    StopScrubbing();
+    return ui::ER_UNHANDLED;
+  }
+
+  if (scrub_state_ == CANCELLED_SCRUBBING)
+    return ui::ER_UNHANDLED;
+
+  if (scrub_state_ == NOT_SCRUBBING) {
+    StartScrubbing();
+    last_transition_position_ = event->root_location();
+    return ui::ER_HANDLED;
+  }
+
+  gfx::Point event_location = event->root_location();
+  int delta_x = event_location.x() - last_transition_position_.x();
+  int delta_y = event_location.y() - last_transition_position_.y();
+  if (std::abs(delta_x) > kMaxHorizontalMovementPerWorkspaceStep) {
+    scrub_state_ = CANCELLED_SCRUBBING;

[sky, 2012/11/28 15:15:34]

What is the rationale for cancelling when you move far enough in the
x-coordinate? Especially since last_transition_position_ is reset on 117.

[pkotwicz, 2012/11/29 01:01:46]

The intent of this old code was to allow horizontal scrub events to go to the
tab scrubber (not be consumed by the workspace cycler)

In the CL I just posted:
- I removed CANCELLED_SCRUBBING state.
- reset last_transition_position_in_root_ such that we don't switch workspaces
when a user scrubs through a whole bunch of tabs and over the course of
scrubbing through (eg 10) tabs moves the required amount to scrub through one
workspace
- Don't consume the mouse event unless the event causes a switch in the active
workspace. This is not ideal for mouse events because the control dragging may
trigger other mouse handlers listening for drags. However this state is
temporary because we want to move to triggering scrubbing on three finger swipes
in the near term

+    return ui::ER_UNHANDLED;
+  }
+
+  if (std::abs(delta_y) > kWorkspaceStepSize) {
+    if (delta_y > 0) {
+      workspace_manager_->CycleToWorkspace(WorkspaceManager::WORKSPACE_BELOW);

[sky, 2012/11/28 15:15:34]

Wow, we really don't let you cycle to the previous?

[pkotwicz, 2012/11/29 01:01:46]

I believe that there are two cases where this code prevents cycling to a
previous workspace:
- when the initial workspace is the desktop. (This is the correct behavior in my
opinion)
- cycling is disabled to workspaces created while cycling through workspaces.
(This is a bug in my opinion and I plan on fixing it once I look into the proper
animations for cycling between workspaces)

+    } else {
+      // If the initial workspace is visible, then cycling to workspaces above
+      // should be disabled as not to scrub to workspaces above the initial
+      // workspace.
+      if (!initial_workspace_window_->IsVisible())
+        workspace_manager_->CycleToWorkspace(WorkspaceManager::WORKSPACE_ABOVE);
+    }
+
+    last_transition_position_ = event_location;
+  }
+
+  return ui::ER_HANDLED;
+}
+
+}  // namespace internal
+}  // namespace ash