Autoscroll new background tabs on iPad

ios/chrome/browser/ui/tabs/tab_strip_controller.mm

 // Copyright 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.
 
 #import "ios/chrome/browser/ui/tabs/tab_strip_controller.h"
 #import "ios/chrome/browser/ui/tabs/tab_strip_controller_private.h"
 
 #include <cmath>
 #include <vector>
 
@@ skipping 297 matching lines @@
 - (NSUInteger)maxNumCollapsedTabs;
 
 // Returns the tab overlap width depending on the current layout mode.
 - (CGFloat)tabOverlap;
 
 // Returns the minimum tab view width depending on the current layout mode.
 - (CGFloat)minTabWidth;
 
 // Updates the content offset of the tab strip view in order to keep the
 // selected tab view visible.
-// Content offset adjustement is only needed/performed in compact mode.
+// Content offset adjustement is only needed/performed in compact mode or
+// regular mode for newly opened tabs.
 // This method must be called with a valid |tabIndex|.
-- (void)updateContentOffsetForTabIndex:(NSUInteger)tabIndex;
+- (void)updateContentOffsetForTabIndex:(NSUInteger)tabIndex
+                              isNewTab:(BOOL)isNewTab;
 
 // Update the frame of the tab strip view (scrollview) frame, content inset and
 // toggle buttons states depending on the current layout mode.
 - (void)updateScrollViewFrameForToggleButton;
 
 @end
 
 @implementation TabStripController
 
 @synthesize buttonNewTab = _buttonNewTab;
@@ skipping 301 matching lines @@
   NSUInteger index = [self modelIndexForTabView:(TabView*)sender];
   DCHECK_NE(NSNotFound, static_cast<NSInteger>(index));
   if (index == NSNotFound)
     return;
   Tab* tappedTab = [_tabModel tabAtIndex:index];
   Tab* currentTab = [_tabModel currentTab];
   if (IsIPadIdiom() && (currentTab != tappedTab)) {
     [currentTab updateSnapshotWithOverlay:YES visibleFrameOnly:YES];
   }
   [_tabModel setCurrentTab:tappedTab];
-  [self updateContentOffsetForTabIndex:index];
+  [self updateContentOffsetForTabIndex:index isNewTab:NO];
 }
 
 - (void)closeTab:(id)sender {
   // Ignore taps while in reordering mode.
   // TODO(rohitrao): We should just hide the close buttons instead.
   if ([self isReorderingTabs])
     return;
 
   base::RecordAction(UserMetricsAction("MobileTabStripCloseTab"));
   DCHECK([sender isKindOfClass:[UIButton class]]);
@@ skipping 283 matching lines @@
 - (void)tabModel:(TabModel*)model
     didInsertTab:(Tab*)tab
          atIndex:(NSUInteger)modelIndex
     inForeground:(BOOL)fg {
   TabView* view = [self tabViewForTab:tab isSelected:fg];
   [_tabArray insertObject:view atIndex:[self indexForModelIndex:modelIndex]];
   [[self tabStripView] addSubview:view];
 
   [self updateContentSizeAndRepositionViews];
   [self setNeedsLayoutWithAnimation];
-  [self updateContentOffsetForTabIndex:modelIndex];
+  [self updateContentOffsetForTabIndex:modelIndex isNewTab:YES];
 }
 
 // Observer method.
 - (void)tabModel:(TabModel*)model
     didRemoveTab:(Tab*)tab
          atIndex:(NSUInteger)modelIndex {
   // Keep the actual view around while it is animating out.  Once the animation
   // is done, remove the view.
   NSUInteger index = [self indexForModelIndex:modelIndex];
   TabView* view = [_tabArray objectAtIndex:index];
@@ skipping 286 matching lines @@
 }
 
 - (CGFloat)tabOverlap {
   return IsCompactTablet() ? kTabOverlapForCompactLayout : kTabOverlap;
 }
 
 - (CGFloat)minTabWidth {
   return IsCompactTablet() ? kMinTabWidthForCompactLayout : kMinTabWidth;
 }
 
-- (void)updateContentOffsetForTabIndex:(NSUInteger)tabIndex {
+- (void)updateContentOffsetForTabIndex:(NSUInteger)tabIndex
+                              isNewTab:(BOOL)isNewTab {
   DCHECK_NE(NSNotFound, static_cast<NSInteger>(tabIndex));
 
+  if (experimental_flags::IsTabStripAutoScrollNewTabsEnabled() && isNewTab) {
+    // The following code calculates the amount of scroll needed to make
+    // |tabIndex| visible in the "virtual" coordinate system, where root is x=0
+    // and it contains all the tabs laid out as if the tabstrip was infinitely
+    // long. The amount of scroll is calculated as a desired length that it is
+    // just large enough to contain all the tabs to the left of |tabIndex|, with
+    // the standard overlap.
+    NSUInteger numNonClosingTabsToLeft = 0;
+    NSUInteger i = 0;
+    for (TabView* tab in _tabArray.get()) {
+      if ([_closingTabs containsObject:tab])
+        ++i;
+
+      if (i == tabIndex)
+        break;
+
+      ++numNonClosingTabsToLeft;
+      ++i;
+    }
+
+    const CGFloat tabHeight = CGRectGetHeight([_tabStripView bounds]);
+    CGRect scrollRect =
+        CGRectMake(_currentTabWidth * numNonClosingTabsToLeft -
+                       ([self tabOverlap] * (numNonClosingTabsToLeft - 1)),
+                   0, _currentTabWidth, tabHeight);
+    [_tabStripView scrollRectToVisible:scrollRect animated:YES];
+    return;
+  }
+
   if (IsCompactTablet()) {
     if (tabIndex == [_tabArray count] - 1) {
       const CGFloat tabStripAvailableSpace =
           _tabStripView.frame.size.width - _tabStripView.contentInset.right;
       if (_tabStripView.contentSize.width > tabStripAvailableSpace) {
         CGFloat scrollToPoint =
             _tabStripView.contentSize.width - tabStripAvailableSpace;
         [_tabStripView setContentOffset:CGPointMake(scrollToPoint, 0)
                                animated:YES];
       }
@@ skipping 330 matching lines @@
                      }
                      completion:nil];
   }
 }
 
 - (void)traitCollectionDidChange:(UITraitCollection*)previousTraitCollection {
   [self updateScrollViewFrameForToggleButton];
   [self updateContentSizeAndRepositionViews];
   NSUInteger selectedModelIndex = [_tabModel indexOfTab:[_tabModel currentTab]];
   if (selectedModelIndex != NSNotFound) {
-    [self updateContentOffsetForTabIndex:selectedModelIndex];
+    [self updateContentOffsetForTabIndex:selectedModelIndex isNewTab:NO];
   }
 }
 
 - (void)setNeedsLayoutWithAnimation {
   _animateLayout = YES;
   [_tabStripView setNeedsLayout];
 }
 
 @end
 
@@ skipping 40 matching lines @@
 
 @implementation TabStripController (Testing)
 
 - (TabView*)existingTabViewForTab:(Tab*)tab {
   NSUInteger tabIndex = [_tabModel indexOfTab:tab];
   NSUInteger tabViewIndex = [self indexForModelIndex:tabIndex];
   return [_tabArray objectAtIndex:tabViewIndex];
 }
 
 @end