CrOS Tablet Window management - Split Screen part I

ash/wm/splitview/split_view_controller.cc

+// Copyright 2017 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/splitview/split_view_controller.h"
+
+#include "ash/ash_switches.h"
+#include "ash/public/cpp/shell_window_ids.h"
+#include "ash/screen_util.h"
+#include "ash/shell.h"
+#include "ash/wm/maximize_mode/maximize_mode_controller.h"
+#include "ash/wm/mru_window_tracker.h"
+#include "ash/wm/window_state.h"
+#include "ash/wm/window_util.h"
+#include "ash/wm/wm_event.h"
+#include "base/command_line.h"
+#include "ui/aura/window.h"
+#include "ui/wm/core/coordinate_conversion.h"
+#include "ui/wm/public/activation_client.h"
+
+namespace ash {
+
+namespace {
+
+// Returns true if |window| can be activated and snapped.
+bool CanSnap(aura::Window* window) {
+  if (!wm::CanActivateWindow(window))
+    return false;
+  return wm::GetWindowState(window)->CanSnap();

[oshima, 2017/06/28 17:36:36]

nit: return CanActivate ? CanSnap : false;

[xdai1, 2017/06/28 18:48:16]

Done.

+}
+
+}  // namespace
+
+SplitViewController::SplitViewController() {
+  Shell::Get()->AddShellObserver(this);
+  Shell::Get()->activation_client()->AddObserver(this);
+}
+
+SplitViewController::~SplitViewController() {
+  Shell::Get()->RemoveShellObserver(this);
+  Shell::Get()->activation_client()->RemoveObserver(this);
+  EndSplitView();
+}
+
+// static
+bool SplitViewController::ShouldAllowSplitView() {
+  if (!base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kAshEnableTabletSplitView)) {
+    return false;
+  }
+  if (!Shell::Get()
+           ->maximize_mode_controller()
+           ->IsMaximizeModeWindowManagerEnabled()) {
+    return false;
+  }
+  return true;
+}
+
+bool SplitViewController::IsSplitViewModeActive() const {
+  return state_ != NOSNAP;
+}
+
+void SplitViewController::SetLeftWindow(aura::Window* left_window) {

[oshima, 2017/06/28 17:36:36]

This method looks pretty much same as SetRightWindow except that left/right is
swapped. 
Maybe it's ok, but may want to try somethign like

pass "the other window" and state, and reset the "other window" if the
left_window matches the other window's reference, and so forth.

[xdai1, 2017/06/28 18:48:16]

I tried to merge these two functions into one function, but it doesn't seem it
can reuse codes and simplify the function. Instead I needed to introduce more
if-clause which increased the function complexity. As such I prefer to keep the
two functions the way it looks in the old patch.

[oshima, 2017/06/28 19:47:47]

Thanks for trying. If it didn't help, then this is fine as it's cleaner.

+  if (!left_window)
+    return;

[oshima, 2017/06/28 17:36:36]

can this happen? If it shouldn't happen, then DCHECK is better option

[xdai1, 2017/06/28 18:48:16]

Done.

+
+  if (state_ == NOSNAP)
+    Shell::Get()->NotifySplitViewModeStarting();
+
+  if (right_window_ == left_window) {
+    StopObserving(right_window_);
+    right_window_ = nullptr;
+  }
+  if (left_window_ != left_window) {
+    StopObserving(left_window_);
+    left_window_ = nullptr;

[oshima, 2017/06/28 17:36:36]

not necessary?

[xdai1, 2017/06/28 18:48:16]

Done.

+    left_window_ = left_window;
+    left_window_->AddObserver(this);
+    wm::GetWindowState(left_window_)->AddObserver(this);
+  }
+
+  State previous_state = state_;
+  switch (state_) {
+    case NOSNAP:
+      default_snap_position_ = LEFT;
+      state_ = LEFT_SNAPPED;
+      break;
+    case LEFT_SNAPPED:
+      state_ = LEFT_SNAPPED;
+      break;
+    case RIGHT_SNAPPED:
+    case BOTH_SNAPPED:
+      state_ = BOTH_SNAPPED;
+      break;
+  }
+
+  const wm::WMEvent event(wm::WM_EVENT_SNAP_LEFT);
+  wm::GetWindowState(left_window_)->OnWMEvent(&event);
+  wm::ActivateWindow(left_window_);
+
+  NotifySplitViewStateChanged(previous_state, state_);
+}
+
+void SplitViewController::SetRightWindow(aura::Window* right_window) {
+  if (!right_window)
+    return;
+
+  if (state_ == NOSNAP)
+    Shell::Get()->NotifySplitViewModeStarting();
+
+  if (left_window_ == right_window) {
+    StopObserving(left_window_);
+    left_window_ = nullptr;
+  }
+  if (right_window_ != right_window) {
+    StopObserving(right_window_);
+    right_window_ = nullptr;

[oshima, 2017/06/28 17:36:36]

ditto

[xdai1, 2017/06/28 18:48:16]

Done.

+    right_window_ = right_window;
+    right_window_->AddObserver(this);
+    wm::GetWindowState(right_window_)->AddObserver(this);
+  }
+
+  State previous_state = state_;
+  switch (state_) {
+    case NOSNAP:
+      default_snap_position_ = RIGHT;
+      state_ = RIGHT_SNAPPED;
+      break;
+    case RIGHT_SNAPPED:
+      state_ = RIGHT_SNAPPED;
+      break;
+    case LEFT_SNAPPED:
+    case BOTH_SNAPPED:
+      state_ = BOTH_SNAPPED;
+      break;
+  }
+
+  const wm::WMEvent event(wm::WM_EVENT_SNAP_RIGHT);
+  wm::GetWindowState(right_window_)->OnWMEvent(&event);
+  wm::ActivateWindow(right_window_);
+
+  NotifySplitViewStateChanged(previous_state, state_);
+}
+
+aura::Window* SplitViewController::GetDefaultSnappedWindow() {
+  if (default_snap_position_ == LEFT)
+    return left_window_;
+  if (default_snap_position_ == RIGHT)
+    return right_window_;
+  return nullptr;
+}
+
+gfx::Rect SplitViewController::GetSnappedWindowBoundsInParent(
+    aura::Window* window,
+    State snap_state) {
+  if (snap_state == LEFT_SNAPPED)
+    return GetLeftWindowBoundsInParent(window);
+  else if (snap_state == RIGHT_SNAPPED)
+    return GetRightWindowBoundsInParent(window);
+
+  NOTREACHED();
+  return gfx::Rect();
+}
+
+gfx::Rect SplitViewController::GetSnappedWindowBoundsInScreen(
+    aura::Window* window,
+    State snap_state) {
+  if (snap_state == LEFT_SNAPPED)
+    return GetLeftWindowBoundsInScreen(window);
+  else if (snap_state == RIGHT_SNAPPED)
+    return GetRightWindowBoundsInScreen(window);
+
+  NOTREACHED();
+  return gfx::Rect();
+}
+
+gfx::Rect SplitViewController::GetDisplayWorkAreaBoundsInParent(
+    aura::Window* window) {
+  aura::Window* root_window = window->GetRootWindow();
+  gfx::Rect bounds_in_parent = ScreenUtil::GetDisplayWorkAreaBoundsInParent(
+      root_window->GetChildById(kShellWindowId_DefaultContainer));

[oshima, 2017/06/28 17:36:36]

just return?

[xdai1, 2017/06/28 18:48:16]

Done.

+  return bounds_in_parent;
+}
+
+gfx::Rect SplitViewController::GetDisplayWorkAreaBoundsInScreen(
+    aura::Window* window) {
+  gfx::Rect bounds = GetDisplayWorkAreaBoundsInParent(window);
+  ::wm::ConvertRectToScreen(window->GetRootWindow(), &bounds);
+  return bounds;
+}
+
+void SplitViewController::AddObserver(Observer* observer) {
+  observers_.AddObserver(observer);
+}
+
+void SplitViewController::RemoveObserver(Observer* observer) {
+  observers_.RemoveObserver(observer);
+}
+
+void SplitViewController::OnWindowDestroying(aura::Window* window) {
+  // If one of the snapped window gets closed, end the split view mode. The
+  // behavior might change in the future.
+  DCHECK(window == left_window_ || window == right_window_);
+  EndSplitView();
+}
+
+void SplitViewController::OnPostWindowStateTypeChange(
+    ash::wm::WindowState* window_state,
+    ash::wm::WindowStateType old_type) {
+  if (window_state->IsFullscreen() || window_state->IsMinimized() ||
+      window_state->IsMaximized()) {
+    // TODO(xdai): Decide what to do if one of the snapped windows gets
+    // minimized /maximized / full-screened. For now we end the split view mode
+    // for simplicity.
+    EndSplitView();
+  }
+}
+
+void SplitViewController::OnWindowActivated(ActivationReason reason,
+                                            aura::Window* gained_active,
+                                            aura::Window* lost_active) {
+  if (!IsSplitViewModeActive())
+    return;
+
+  // If |gained_active| was activated as a side effect of a window disposition
+  // change, do nothing. For example, when a snapped window is closed, another
+  // window will be activated before OnWindowDestroying() is called. We should
+  // not try to snap another window in this case.
+  if (reason == ActivationReason::WINDOW_DISPOSITION_CHANGED)
+    return;
+
+  // Only snap window that can be snapped but hasn't been snapped.
+  if (!gained_active || gained_active == left_window_ ||
+      gained_active == right_window_ || !CanSnap(gained_active)) {
+    return;
+  }
+
+  // Only window in MRU list can be snapped.
+  aura::Window::Windows windows =
+      Shell::Get()->mru_window_tracker()->BuildMruWindowList();
+  if (std::find(windows.begin(), windows.end(), gained_active) == windows.end())
+    return;
+
+  // Snap the window on the non-default side of the screen if split view mode
+  // is active.
+  if (default_snap_position_ == LEFT)
+    SetRightWindow(gained_active);
+  else
+    SetLeftWindow(gained_active);
+}
+
+void SplitViewController::OnOverviewModeStarting() {
+  // If split view mode is active, reset |state_| to make it be able to select
+  // another window from overview window grid.
+  if (IsSplitViewModeActive()) {
+    DCHECK(state_ == BOTH_SNAPPED);

[oshima, 2017/06/28 17:36:36]

DCHECK_EQ

but is this true? What if I enter the overview mode when only one window is
snapped?

[xdai1, 2017/06/28 18:48:16]

Yes, theoretically the state must be BOTH_SNAPPED. If there is only one window
snapped, which means MRU windows list only contains one window, and we won't
enter the overview mode in this case. However, your question reminds me that we
can have windows/ARC apps that could not be snapped thus it's possible that we
only have 1 snapped window while MRU windows list contains more than 1 window.
Removed the DCHECK here.

[oshima, 2017/06/28 19:47:47]

Ack.

+    if (default_snap_position_ == LEFT) {
+      StopObserving(right_window_);
+      state_ = LEFT_SNAPPED;
+    } else {
+      StopObserving(left_window_);
+      state_ = RIGHT_SNAPPED;
+    }
+    NotifySplitViewStateChanged(BOTH_SNAPPED, state_);
+  }
+}
+
+void SplitViewController::OnOverviewModeEnded() {
+  // If split view mode is active but only has one snapped window, use the MRU
+  // window list to auto select another window to snap.
+  if (IsSplitViewModeActive() && state_ != BOTH_SNAPPED) {
+    aura::Window::Windows windows =
+        Shell::Get()->mru_window_tracker()->BuildMruWindowList();
+    auto end = std::remove_if(windows.begin(), windows.end(),
+                              std::not1(std::ptr_fun(&CanSnap)));
+    windows.resize(end - windows.begin());
+    for (auto* window : windows) {

[oshima, 2017/06/28 17:36:36]

It's probably faster to simply skip !CanSnap in the loop.

[xdai1, 2017/06/28 18:48:16]

Done.

+      if (window != GetDefaultSnappedWindow()) {
+        if (default_snap_position_ == LEFT)
+          SetRightWindow(window);
+        else
+          SetLeftWindow(window);
+        break;
+      }
+    }
+  }
+}
+
+void SplitViewController::EndSplitView() {
+  StopObserving(left_window_);
+  StopObserving(right_window_);
+  left_window_ = nullptr;
+  right_window_ = nullptr;
+  default_snap_position_ = LEFT;
+  divider_position_ = -1;
+
+  State previous_state = state_;
+  state_ = NOSNAP;
+  NotifySplitViewStateChanged(previous_state, state_);
+
+  Shell::Get()->NotifySplitViewModeEnded();
+}
+
+void SplitViewController::StopObserving(aura::Window* window) {
+  if (window) {
+    window->RemoveObserver(this);
+    if (wm::GetWindowState(window))
+      wm::GetWindowState(window)->RemoveObserver(this);
+  }
+}
+
+void SplitViewController::NotifySplitViewStateChanged(State previous_state,
+                                                      State state) {
+  if (previous_state == state)
+    return;
+  for (Observer& observer : observers_)
+    observer.OnSplitViewStateChanged(previous_state, state);
+}
+
+gfx::Rect SplitViewController::GetLeftWindowBoundsInParent(
+    aura::Window* window) {
+  gfx::Rect bounds = GetLeftWindowBoundsInScreen(window);
+  ::wm::ConvertRectFromScreen(window->GetRootWindow(), &bounds);
+  return bounds;
+}
+
+gfx::Rect SplitViewController::GetRightWindowBoundsInParent(
+    aura::Window* window) {
+  gfx::Rect bounds = GetRightWindowBoundsInScreen(window);
+  ::wm::ConvertRectFromScreen(window->GetRootWindow(), &bounds);
+  return bounds;
+}
+
+gfx::Rect SplitViewController::GetLeftWindowBoundsInScreen(
+    aura::Window* window) {
+  const gfx::Rect display_bounds_in_screen =
+      GetDisplayWorkAreaBoundsInScreen(window);
+  if (divider_position_ < 0) {
+    divider_position_ =
+        display_bounds_in_screen.x() + display_bounds_in_screen.width() * 0.5f;
+  }
+  return gfx::Rect(display_bounds_in_screen.x(), display_bounds_in_screen.y(),
+                   divider_position_ - display_bounds_in_screen.x(),
+                   display_bounds_in_screen.height());
+}
+
+gfx::Rect SplitViewController::GetRightWindowBoundsInScreen(
+    aura::Window* window) {
+  const gfx::Rect display_bounds_in_screen =
+      GetDisplayWorkAreaBoundsInScreen(window);
+  if (divider_position_ < 0) {
+    divider_position_ =
+        display_bounds_in_screen.x() + display_bounds_in_screen.width() * 0.5f;
+  }
+  return gfx::Rect(divider_position_, display_bounds_in_screen.y(),
+                   display_bounds_in_screen.x() +
+                       display_bounds_in_screen.width() - divider_position_,
+                   display_bounds_in_screen.height());
+}
+
+}  // namespace ash