[ash-md] Improves smoothness with many windows in overview

ash/common/wm/overview/window_grid.cc

 // Copyright 2014 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/common/wm/overview/window_grid.h"
 
 #include <algorithm>
 #include <functional>
 #include <set>
 #include <utility>
@@ skipping 12 matching lines @@
 #include "ash/common/wm/overview/window_selector_delegate.h"
 #include "ash/common/wm/overview/window_selector_item.h"
 #include "ash/common/wm/window_state.h"
 #include "ash/common/wm/wm_screen_util.h"
 #include "ash/common/wm_lookup.h"
 #include "ash/common/wm_root_window_controller.h"
 #include "ash/common/wm_window.h"
 #include "base/command_line.h"
 #include "base/i18n/string_search.h"
 #include "base/memory/scoped_vector.h"
+#include "base/strings/string_number_conversions.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "third_party/skia/include/pathops/SkPathOps.h"
 #include "ui/compositor/layer_animation_observer.h"
 #include "ui/compositor/scoped_layer_animation_settings.h"
 #include "ui/gfx/animation/tween.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/geometry/safe_integer_conversions.h"
 #include "ui/gfx/geometry/vector2d.h"
 #include "ui/gfx/scoped_canvas.h"
 #include "ui/views/background.h"
@@ skipping 22 matching lines @@
 
 // Conceptually the window overview is a table or grid of cells having this
 // fixed aspect ratio. The number of columns is determined by maximizing the
 // area of them based on the number of window_list.
 const float kCardAspectRatio = 4.0f / 3.0f;
 
 // The minimum number of cards along the major axis (i.e. horizontally on a
 // landscape orientation).
 const int kMinCardsMajor = 3;
 
+// Hiding window headers can be resource intensive. Only hide the headers when
+// the number of windows in this grid is less or equal than this number.
+const int kMaxWindowsCountToHideHeader = 10;
+
 const int kOverviewSelectorTransitionMilliseconds = 250;
 
 // The color and opacity of the screen shield in overview.
 const SkColor kShieldColor = SkColorSetARGB(255, 0, 0, 0);
 const float kShieldOpacity = 0.7f;
 
 // The color and opacity of the overview selector.
 const SkColor kWindowSelectionColor = SkColorSetARGB(128, 0, 0, 0);
 const SkColor kWindowSelectionColorMD = SkColorSetARGB(51, 255, 255, 255);
 const SkColor kWindowSelectionBorderColor = SkColorSetARGB(38, 255, 255, 255);
@@ skipping 359 matching lines @@
 void WindowGrid::PrepareForOverview() {
   if (ash::MaterialDesignController::IsOverviewMaterial())
     InitShieldWidget();
   for (auto iter = window_list_.begin(); iter != window_list_.end(); ++iter)
     (*iter)->PrepareForOverview();
 }
 
 void WindowGrid::PositionWindowsMD(bool animate) {
   if (window_list_.empty())
     return;
+
+  const int kUnlimited = -1;
+  const size_t windows_count = window_list_.size();
+  const base::CommandLine* command_line =
+      base::CommandLine::ForCurrentProcess();
+  int windows_to_use_masks = kMaxWindowsCountToHideHeader;
+  if (command_line->HasSwitch(switches::kAshMaxWindowsToUseMaskInOverview) &&
+      (!base::StringToInt(command_line->GetSwitchValueASCII(
+                              switches::kAshMaxWindowsToUseMaskInOverview),
+                          &windows_to_use_masks) ||
+       windows_to_use_masks <= kUnlimited)) {
+    windows_to_use_masks = kMaxWindowsCountToHideHeader;
+  }
+  int windows_to_use_shapes = kUnlimited;
+  if (command_line->HasSwitch(switches::kAshMaxWindowsToUseShapeInOverview) &&
+      (!base::StringToInt(command_line->GetSwitchValueASCII(
+                              switches::kAshMaxWindowsToUseShapeInOverview),
+                          &windows_to_use_shapes) ||
+       windows_to_use_shapes <= kUnlimited)) {
+    windows_to_use_shapes = kUnlimited;
+  }
+  WindowSelectorItem::set_use_mask(windows_to_use_masks <= kUnlimited ||
+                                   static_cast<int>(windows_count) <=
+                                       windows_to_use_masks);
+  WindowSelectorItem::set_use_shape(windows_to_use_shapes <= kUnlimited ||
+                                    static_cast<int>(windows_count) <=
+                                        windows_to_use_shapes);
+
   gfx::Rect total_bounds =
       root_window_->ConvertRectToScreen(wm::GetDisplayWorkAreaBoundsInParent(
           root_window_->GetChildByShellWindowId(
               kShellWindowId_DefaultContainer)));
   // Windows occupy vertically centered area with additional vertical insets.
   int horizontal_inset =
       gfx::ToFlooredInt(std::min(kOverviewInsetRatio * total_bounds.width(),
                                  kOverviewInsetRatio * total_bounds.height()));
   int vertical_inset =
       horizontal_inset +
@@ skipping 88 matching lines @@
   // |right_bound| was reverted. Perform one last pass to position the |rects|.
   if (make_last_adjustment) {
     gfx::Rect overview_bounds(total_bounds);
     overview_bounds.set_width(right_bound - total_bounds.x());
     FitWindowRectsInBounds(overview_bounds,
                            std::min(kMaxHeight + 2 * kWindowMarginMD, height),
                            &rects, &max_bottom, &min_right, &max_right);
   }
   // Position the windows centering the left-aligned rows vertically.
   gfx::Vector2d offset(0, (total_bounds.bottom() - max_bottom) / 2);
-  for (size_t i = 0; i < window_list_.size(); ++i) {
+  for (size_t i = 0; i < windows_count; ++i) {
     window_list_[i]->SetBounds(
         rects[i] + offset,
         animate
             ? OverviewAnimationType::OVERVIEW_ANIMATION_LAY_OUT_SELECTOR_ITEMS
             : OverviewAnimationType::OVERVIEW_ANIMATION_NONE);
   }
 
   // If the selection widget is active, reposition it without any animation.
   if (selection_widget_)
     MoveSelectionWidgetToTarget(animate);
@@ skipping 409 matching lines @@
         *min_right = left;
       if (*max_right < left)
         *max_right = left;
     }
     *max_bottom = top + height;
   }
   return windows_fit;
 }
 
 }  // namespace ash