Snap widgets to pixel boundary on ash

ash/root_window_controller.cc

Index: ash/root_window_controller.cc
diff --git a/ash/root_window_controller.cc b/ash/root_window_controller.cc
index 60018d5be523d3ee766cbe4da0e3264325008969..1a9a50c75e90465daaf8238b4261867c87f9d3f3 100644
--- a/ash/root_window_controller.cc
+++ b/ash/root_window_controller.cc
@@ -856,6 +856,10 @@ void RootWindowController::InitLayoutManagers() {
       new DockedWindowLayoutManager(docked_container, workspace_controller());
   docked_container->SetLayoutManager(docked_layout_manager_);
 
+  // Installs SnapLayoutManager to containers who set the
+  // |kSnapsChildrenToPhysicalPixelBoundary| property.
+  wm::InstallSnapLayoutManagerToContainers(root_window);
+

[Jun Mukai, 2014/07/16 22:59:08]

Not sure why this is necessary.  Instead of setting the property below, why not
just setting the SnapToPixelLayoutManager there?

[oshima, 2014/07/17 22:07:56]

Because some containers may install its own layout managers, and I wanted to
keep it more declarative. (I will change CreateContainer to
take bitmap flags that specifies, this , screen coordinates, animation and so
forth, but in separate CL)

I can be convinced the other way though.

[Jun Mukai, 2014/07/17 22:26:31]

Hmm, I don't get the point.

If a container with the snap-to-pixel property installs its own layout manager,
the layout manager implementation should respect the property, or inherit
SnapToPixelLayoutManager. Otherwise, the property is just ignored. Right?

Then, the declaration doesn't help the situation so much. The implementers need
to care about SnapToPixelLayoutManager anyways.

How about this:
- keep this class and InstallSnapLayoutManagerToContainers().
  This class is solely responsible for the SnapToPixel property setups.
- in ctor of SnapToPixelLayoutManager, don't set property. Instead, add a DCHECK
to verify if the declarations (i.e. this class) is correct.

[Jun Mukai, 2014/07/17 22:27:16]

ah, your new patchset is in this way. Thanks for quick work.

[oshima, 2014/07/17 22:28:40]

Sorry, I should have mentioned that.

   // Create Panel layout manager
   aura::Window* panel_container = GetContainer(kShellWindowId_PanelContainer);
   panel_layout_manager_ = new PanelLayoutManager(panel_container);
@@ -984,12 +988,14 @@ void RootWindowController::CreateContainersInRootWindow(
       kShellWindowId_PanelContainer,
       "PanelContainer",
       non_lock_screen_containers);
+  wm::SetSnapsChildrenToPhysicalPixelBoundary(panel_container);
   SetUsesScreenCoordinates(panel_container);
 
   aura::Window* shelf_bubble_container =
       CreateContainer(kShellWindowId_ShelfBubbleContainer,
                       "ShelfBubbleContainer",
                       non_lock_screen_containers);
+  wm::SetSnapsChildrenToPhysicalPixelBoundary(shelf_bubble_container);
   SetUsesScreenCoordinates(shelf_bubble_container);
   DescendantShouldStayInSameRootWindow(shelf_bubble_container);
 
@@ -997,6 +1003,7 @@ void RootWindowController::CreateContainersInRootWindow(
       CreateContainer(kShellWindowId_AppListContainer,
                       "AppListContainer",
                       non_lock_screen_containers);
+  wm::SetSnapsChildrenToPhysicalPixelBoundary(app_list_container);
   SetUsesScreenCoordinates(app_list_container);
 
   aura::Window* modal_container = CreateContainer(
@@ -1047,6 +1054,7 @@ void RootWindowController::CreateContainersInRootWindow(
       "SettingBubbleContainer",
       lock_screen_related_containers);
   ::wm::SetChildWindowVisibilityChangesAnimated(settings_bubble_container);
+  wm::SetSnapsChildrenToPhysicalPixelBoundary(settings_bubble_container);
   SetUsesScreenCoordinates(settings_bubble_container);
   DescendantShouldStayInSameRootWindow(settings_bubble_container);
 
@@ -1055,6 +1063,7 @@ void RootWindowController::CreateContainersInRootWindow(
       "MenuContainer",
       lock_screen_related_containers);
   ::wm::SetChildWindowVisibilityChangesAnimated(menu_container);
+  wm::SetSnapsChildrenToPhysicalPixelBoundary(menu_container);
   SetUsesScreenCoordinates(menu_container);
 
   aura::Window* drag_drop_container = CreateContainer(
@@ -1062,18 +1071,22 @@ void RootWindowController::CreateContainersInRootWindow(
       "DragImageAndTooltipContainer",
       lock_screen_related_containers);
   ::wm::SetChildWindowVisibilityChangesAnimated(drag_drop_container);
+  wm::SetSnapsChildrenToPhysicalPixelBoundary(drag_drop_container);
   SetUsesScreenCoordinates(drag_drop_container);
 
   aura::Window* overlay_container = CreateContainer(
       kShellWindowId_OverlayContainer,
       "OverlayContainer",
       lock_screen_related_containers);
+  wm::SetSnapsChildrenToPhysicalPixelBoundary(overlay_container);
   SetUsesScreenCoordinates(overlay_container);
 
   aura::Window* virtual_keyboard_parent_container = CreateContainer(
       kShellWindowId_VirtualKeyboardParentContainer,
       "VirtualKeyboardParentContainer",
       root_window);
+  wm::SetSnapsChildrenToPhysicalPixelBoundary(
+      virtual_keyboard_parent_container);
   SetUsesScreenCoordinates(virtual_keyboard_parent_container);
 
 #if defined(OS_CHROMEOS)