Refine snap scrolling on the Cards New Tab Page.

chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPageView.java

Index: chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPageView.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPageView.java b/chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPageView.java
index f6c875ccb5e14d0c7ea69f303fc5e8cb35a3f3c8..a958694418ddee9efc3fe48a0fb6900133fa03b6 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPageView.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPageView.java
@@ -45,7 +45,6 @@ import org.chromium.chrome.browser.ntp.LogoBridge.LogoObserver;
 import org.chromium.chrome.browser.ntp.MostVisitedItem.MostVisitedItemManager;
 import org.chromium.chrome.browser.ntp.NewTabPage.OnSearchBoxScrollListener;
 import org.chromium.chrome.browser.ntp.cards.CardItemDecoration;
-import org.chromium.chrome.browser.ntp.cards.CardsLayoutOperations;
 import org.chromium.chrome.browser.ntp.cards.NewTabPageAdapter;
 import org.chromium.chrome.browser.ntp.cards.NewTabPageListItem;
 import org.chromium.chrome.browser.ntp.cards.NewTabPageRecyclerView;
@@ -417,8 +416,14 @@ public class NewTabPageView extends FrameLayout
             // be 100%.
             percentage = 1f;
         } else {
-            percentage = MathUtils.clamp(getVerticalScroll() / (float) mSearchBoxView.getTop(),
-                    0f, 1f);
+            final int scrollY = getVerticalScroll();
+            final int top = mSearchBoxView.getTop();  // Relative to mNewTabPageLayout.
+            final int transitionLength = getResources()
+                    .getDimensionPixelSize(R.dimen.ntp_search_box_transition_length);
+
+            // |scrollY - top| gives the distance the search bar is from the top of the screen.
+            percentage = MathUtils.clamp(
+                    (scrollY - top + transitionLength) / (float) transitionLength, 0f, 1f);
         }
 
         updateVisualsForToolbarTransition(percentage);
@@ -448,23 +453,51 @@ public class NewTabPageView extends FrameLayout
         return viewCount;
     }
 
+    private void snapScroll() {
+        // Snap scroll to prevent resting in the middle of the omnibox transition.
+        final int searchBoxTransitionLength = getResources()
+                .getDimensionPixelSize(R.dimen.ntp_search_box_transition_length);
+        if (mRecyclerView.scrollOutOfRegion(mSearchBoxView.getTop() - searchBoxTransitionLength,
+                                            mSearchBoxView.getTop())) {
+            // The snap scrolling regions should never overlap.
+            return;
+        }
+
+        // Snap scroll to prevent resting in the middle of the peeking card transition
+        // and to allow the peeking card to peek a bit before snapping back.
+        if (mRecyclerView.isPeekingCardVisible() && mRecyclerView.isFirstItemVisible()) {
+            final int peekingHeight = getResources().getDimensionPixelSize(
+                    R.dimen.snippets_padding_and_peeking_card_height);
+
+            // |A + B| gives the offset of the peeking card relative to the Recycler View,
+            // so scrolling to this point would put the peeking card at the top of the
+            // screen.
+            // |A + B - C| will scroll us so that the peeking card is just off the bottom
+            // of the screen.
+            // Finally, we get |A + B - C + D| because the transition starts from the
+            // peeking card's resting point, which is |D| from the bottom of the screen.
+            int start =  mRecyclerView.getPeekingCardTop()  // A.
+                    + getVerticalScroll()  // B.
+                    - getHeight()  // C.
+                    + peekingHeight;  // D.
+            mRecyclerView.scrollOutOfRegion(start,
+                                            start + mRecyclerView.getPeekingCardHeight() / 2,
+                                            start + mRecyclerView.getPeekingCardHeight() / 2);
+        }
+    }
+
     /**
      * Sets up scrolling when snippets are enabled. It adds scroll listeners and touch listeners to
      * the RecyclerView.
      */
     private void initializeSearchBoxRecyclerViewScrollHandling() {
-        final NewTabPageUma.SnapStateObserver snapStateObserver =
-                new NewTabPageUma.SnapStateObserver();
-
         final Runnable mSnapScrollRunnable = new Runnable() {
             @Override
             public void run() {
                 assert mPendingSnapScroll;
                 mPendingSnapScroll = false;
-                NewTabPageUma.SnapState currentSnapState = CardsLayoutOperations.snapScroll(
-                        mRecyclerView, mNewTabPageLayout, mMostVisitedLayout, getVerticalScroll(),
-                        false);
-                snapStateObserver.updateSnapState(NewTabPageView.this, currentSnapState);
+
+                snapScroll();
             }
         };
 
@@ -689,7 +722,6 @@ public class NewTabPageView extends FrameLayout
         // Ensure there are no rounding issues when the animation percent is 0.
         if (transitionPercentage == 0f) searchUiAlpha = 1f;
 
-        mSearchProviderLogoView.setAlpha(searchUiAlpha);

[Bernhard Bauer, 2016/06/28 14:44:00]

Can we also guard this with the cardsUI check?

[PEConn, 2016/06/28 15:39:04]

Done.

         mSearchBoxView.setAlpha(searchUiAlpha);
     }
 
@@ -812,10 +844,8 @@ public class NewTabPageView extends FrameLayout
         if (mUseCardsUi) {
             mRecyclerView.updatePeekingCard();
             // The positioning of elements may have been changed (since the elements expand to fill
-            // the available vertical space), so adjust the scroll. We force snapping to Most Likely
-            // so the user's snap point doesn't change on rotation.
-            CardsLayoutOperations.snapScroll(mRecyclerView, mNewTabPageLayout, mMostVisitedLayout,
-                    getVerticalScroll(), true);
+            // the available vertical space), so adjust the scroll.
+            snapScroll();
         }
     }