Experimental app list: Change transition animations of top-level pages.

ui/app_list/views/contents_view.cc

Index: ui/app_list/views/contents_view.cc
diff --git a/ui/app_list/views/contents_view.cc b/ui/app_list/views/contents_view.cc
index 19c9dd93836895343e2c8637f186e69053dbf31e..6d73740efb679dad0b20dd707dacc70a8d9786ef 100644
--- a/ui/app_list/views/contents_view.cc
+++ b/ui/app_list/views/contents_view.cc
@@ -19,6 +19,7 @@
 #include "ui/app_list/views/search_result_list_view.h"
 #include "ui/app_list/views/start_page_view.h"
 #include "ui/events/event.h"
+#include "ui/gfx/animation/tween.h"
 #include "ui/resources/grit/ui_resources.h"
 #include "ui/views/view_model.h"
 #include "ui/views/view_model_utils.h"
@@ -73,6 +74,7 @@ void ContentsView::InitNamedPages(AppListModel* model,
   int initial_page_index = app_list::switches::IsExperimentalAppListEnabled()
                                ? GetPageIndexForNamedPage(NAMED_PAGE_START)
                                : GetPageIndexForNamedPage(NAMED_PAGE_APPS);
+  DCHECK_GE(initial_page_index, 0);
 
   page_before_search_ = initial_page_index;
   pagination_model_.SelectPage(initial_page_index, false);
@@ -118,20 +120,18 @@ int ContentsView::GetActivePageIndex() const {
 }
 
 bool ContentsView::IsNamedPageActive(NamedPage named_page) const {
-  std::map<NamedPage, int>::const_iterator it =
-      named_page_to_view_.find(named_page);
-  if (it == named_page_to_view_.end())
-    return false;
-  return it->second == GetActivePageIndex();
+  int active_page_index = GetActivePageIndex();
+  return active_page_index >= 0 &&
+         GetPageIndexForNamedPage(named_page) == active_page_index;
 }
 
 int ContentsView::GetPageIndexForNamedPage(NamedPage named_page) const {
   // Find the index of the view corresponding to the given named_page.
   std::map<NamedPage, int>::const_iterator it =
       named_page_to_view_.find(named_page);
-  // GetPageIndexForNamedPage should never be called on a named_page that does
-  // not have a corresponding view.
-  DCHECK(it != named_page_to_view_.end());
+  if (it == named_page_to_view_.end())
+    return -1;
+
   return it->second;
 }
 
@@ -173,6 +173,7 @@ void ContentsView::ShowSearchResults(bool show) {
       app_list::switches::IsExperimentalAppListEnabled()
           ? NAMED_PAGE_START
           : NAMED_PAGE_SEARCH_RESULTS);
+  DCHECK_GE(search_page, 0);
 
   SetActivePageInternal(show ? search_page : page_before_search_, show);
 }
@@ -184,11 +185,19 @@ bool ContentsView::IsShowingSearchResults() const {
              : IsNamedPageActive(NAMED_PAGE_SEARCH_RESULTS);
 }
 
-void ContentsView::UpdatePageBounds() {
-  gfx::Rect rect(GetContentsBounds());
-  if (rect.IsEmpty())
-    return;
+gfx::Rect ContentsView::GetOffscreenPageBounds(int page_index) const {
+  gfx::Rect bounds(GetContentsBounds());
+  // The start page and search page origins are above; all other pages' origins
+  // are below.
+  int page_height = bounds.height();
+  bool origin_above =
+      GetPageIndexForNamedPage(NAMED_PAGE_START) == page_index ||
+      GetPageIndexForNamedPage(NAMED_PAGE_SEARCH_RESULTS) == page_index;
+  bounds.set_y(origin_above ? -page_height : page_height);
+  return bounds;
+}
 
+void ContentsView::UpdatePageBounds() {
   // The bounds calculations will potentially be mid-transition (depending on
   // the state of the PaginationModel).
   int current_page = std::max(0, pagination_model_.selected_page());
@@ -203,20 +212,18 @@ void ContentsView::UpdatePageBounds() {
     }
   }
 
-  gfx::Rect incoming_target(rect);
-  gfx::Rect outgoing_target(rect);
-  int dir = target_page > current_page ? -1 : 1;
-
-  // Pages transition vertically.
-  int page_height = rect.height();
-  int transition_offset = progress * page_height * dir;
-
-  outgoing_target.set_y(transition_offset);
-  incoming_target.set_y(dir < 0 ? transition_offset + page_height
-                                : transition_offset - page_height);
-
-  view_model_->view_at(current_page)->SetBoundsRect(outgoing_target);
-  view_model_->view_at(target_page)->SetBoundsRect(incoming_target);
+  // Move |current_page| from 0 to its origin. Move |target_page| from its
+  // origin to 0.
+  gfx::Rect on_screen(GetContentsBounds());
+  gfx::Rect current_page_origin(GetOffscreenPageBounds(current_page));
+  gfx::Rect target_page_origin(GetOffscreenPageBounds(target_page));
+  gfx::Rect current_page_rect(
+      gfx::Tween::RectValueBetween(progress, on_screen, current_page_origin));
+  gfx::Rect target_page_rect(
+      gfx::Tween::RectValueBetween(progress, target_page_origin, on_screen));
+
+  view_model_->view_at(current_page)->SetBoundsRect(current_page_rect);
+  view_model_->view_at(target_page)->SetBoundsRect(target_page_rect);
 }
 
 PaginationModel* ContentsView::GetAppsPaginationModel() {