NTP, modify the snippet header display to above the peeking card

chrome/android/java/src/org/chromium/chrome/browser/ntp/snippets/SnippetHeaderViewHolder.java

Index: chrome/android/java/src/org/chromium/chrome/browser/ntp/snippets/SnippetHeaderViewHolder.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ntp/snippets/SnippetHeaderViewHolder.java b/chrome/android/java/src/org/chromium/chrome/browser/ntp/snippets/SnippetHeaderViewHolder.java
index 919a1d243b767a962b0c94c84f5dcf9ff5385120..28ec164bb7f56cc8b4abbc45f595964659421568 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/ntp/snippets/SnippetHeaderViewHolder.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ntp/snippets/SnippetHeaderViewHolder.java
@@ -4,9 +4,6 @@
 
 package org.chromium.chrome.browser.ntp.snippets;
 
-import android.animation.Animator;
-import android.animation.AnimatorListenerAdapter;
-import android.animation.ObjectAnimator;
 import android.support.v7.widget.RecyclerView;
 import android.view.LayoutInflater;
 import android.view.View;
@@ -14,90 +11,64 @@ import android.view.ViewGroup;
 
 import org.chromium.chrome.R;
 import org.chromium.chrome.browser.ntp.cards.NewTabPageListItem;
+import org.chromium.chrome.browser.ntp.cards.NewTabPageRecyclerView;
 import org.chromium.chrome.browser.ntp.cards.NewTabPageViewHolder;
+import org.chromium.chrome.browser.util.MathUtils;
 
 /**
  * A class that represents the view for a single card snippet.
  */
 public class SnippetHeaderViewHolder extends NewTabPageViewHolder {
-    private static final int ANIMATION_DURATION_MS = 300;
+    private static final double SCROLL_HEADER_HEIGHT_PERCENTAGE = 0.7;
 
     private final int mMaxSnippetHeaderHeight;
+    private final int mMaxPeekPadding;
+    private final NewTabPageRecyclerView mRecyclerView;
+
     private SnippetHeaderListItem mHeader;
-    private Animator mAnimator;
 
     public static View createView(ViewGroup parent) {
         return LayoutInflater.from(parent.getContext())
                 .inflate(R.layout.new_tab_page_snippets_card, parent, false);
     }
 
-    public SnippetHeaderViewHolder(final View cardView) {
+    public SnippetHeaderViewHolder(final View cardView, final NewTabPageRecyclerView recyclerView) {
         super(cardView);
         mMaxSnippetHeaderHeight = cardView.getResources().getDimensionPixelSize(
                 R.dimen.snippets_article_header_height);
+
+        mMaxPeekPadding = cardView.getResources().getDimensionPixelSize(
+                R.dimen.snippets_padding_and_peeking_card_height);
+
+        mRecyclerView = recyclerView;
     }
 
     @Override
     public void onBindViewHolder(NewTabPageListItem header) {
         mHeader = (SnippetHeaderListItem) header;
-        animateFade();
+        updateDisplay();
     }
 
     /**
-     * Update the view for the scroll-triggered fade in/out animation.
-     * @param omniBoxHeight The height of the omnibox displayed over the NTP, we use this to offset
-     *          the start point of the transition.
+     * Update the view for the fade in/out and heading height.
      */
-    public void onScrolled(int omniBoxHeight) {
+    public void updateDisplay() {
         RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) itemView.getLayoutParams();
         int headerHeight = 0;
-
-        // Measurement used to multiply the max snippet height to get a range on when to start
-        // modifying the display of article header.
-        final int numberHeaderHeight = 2;
-        // Used to indicate when to start modifying the snippet header.
-        int heightToStartChangingHeader = mMaxSnippetHeaderHeight * numberHeaderHeight;
         int snippetHeaderTop = itemView.getTop();
-
-        // Check if snippet header top is within range to start showing the snippet header.
-        if (snippetHeaderTop < omniBoxHeight + heightToStartChangingHeader) {
-            // The amount of space the article header has scrolled into the
-            // |heightToStartChangingHeader|.
-            int amountScrolledIntoHeaderSpace =
-                    heightToStartChangingHeader - (snippetHeaderTop - omniBoxHeight);
-
-            // Remove the |numberHeaderHeight| to get the actual header height we want to
-            // display. Never let the height be more than the |maxSnippetHeaderHeight|.
-            headerHeight = Math.min(
-                    amountScrolledIntoHeaderSpace / numberHeaderHeight, mMaxSnippetHeaderHeight);
-
+        int recyclerViewHeight = mRecyclerView.getHeight();
+
+        // Check if snippet header top is within range to start showing. Set the header height, this
+        // is a percentage of how much is scrolled. The balance of the scroll will
+        // be used to display the peeking card.
+        int amountScrolled = (recyclerViewHeight - mMaxPeekPadding) - snippetHeaderTop;
+        if (mHeader.isVisible()) {
+            headerHeight = MathUtils.clamp((int) (amountScrolled * SCROLL_HEADER_HEIGHT_PERCENTAGE),
+                    0, mMaxSnippetHeaderHeight);
         }
 
-        if (mHeader.isVisible()) itemView.setAlpha((float) headerHeight / mMaxSnippetHeaderHeight);
+        itemView.setAlpha((float) headerHeight / mMaxSnippetHeaderHeight);
         params.height = headerHeight;
-        itemView.setLayoutParams(params);
-    }
-
-    /**
-     * Make the header fade in or out depending on the model's state.
-     * @see SnippetHeaderListItem#isVisible()
-     */
-    private void animateFade() {
-        if (mAnimator != null) mAnimator.cancel();
-
-        float currentAlpha = itemView.getAlpha();
-        float targetAlpha = mHeader.isVisible() ? 1f : 0f;
-
-        if (currentAlpha == targetAlpha) return;
-
-        mAnimator = ObjectAnimator.ofFloat(itemView, View.ALPHA, currentAlpha, targetAlpha);
-        mAnimator.setDuration(ANIMATION_DURATION_MS);
-        mAnimator.addListener(new AnimatorListenerAdapter() {
-            @Override
-            public void onAnimationEnd(Animator animator) {
-                mAnimator = null;
-            }
-        });
-        mAnimator.start();
+        itemView.requestLayout();
     }
 }