From 1f8f88696b8e19dda37b4b3defdc91d557e424bc Mon Sep 17 00:00:00 2001
From: Brandon Dayauon <brdayauon@google.com>
Date: Thu, 2 May 2024 16:24:20 -0700
Subject: [PATCH] Create an alpha letter scroller

- The function used is a raised cosine function to determine the sections to animate.

Tested flag: adb shell device_config put launcher com.android.launcher3.letter_fast_scroller true
Based on recent figmaspec, size of selected letter is 28dp and regular is 20dp. That means scaling should be 28/20.
Colors are:
onSurface for letter
surfaceContainer for background.
Figma shows selected colors are materialColorOnSecondary

bug:358673724
Test manually: https://drive.google.com/file/d/1gvJd5KoK8X_Sv8jXg1cZ65R4AuqHuvcd/view?usp=sharing
Flag: com.android.launcher3.letter_fast_scroller

Change-Id: Ia86eb0e8c41bc043fda3c44aeaf59e204429f337
---
 aconfig/launcher.aconfig                      |   7 +
 res/drawable/bg_letter_list_text.xml          |  23 +++
 res/layout/all_apps_fast_scroller.xml         |  13 ++
 .../fast_scroller_letter_list_text_view.xml   |  24 ++++
 res/values/dimens.xml                         |   5 +
 .../launcher3/FastScrollRecyclerView.java     |  12 +-
 .../allapps/ActivityAllAppsContainerView.java |  19 ++-
 .../allapps/AllAppsRecyclerView.java          |  88 ++++++++++++
 .../allapps/AlphabeticalAppsList.java         |   6 +
 .../launcher3/allapps/LetterListTextView.java | 133 ++++++++++++++++++
 .../views/RecyclerViewFastScroller.java       |  99 +++++++++++--
 .../widget/picker/WidgetsFullSheet.java       |   7 +-
 12 files changed, 415 insertions(+), 21 deletions(-)
 create mode 100644 res/drawable/bg_letter_list_text.xml
 create mode 100644 res/layout/fast_scroller_letter_list_text_view.xml
 create mode 100644 src/com/android/launcher3/allapps/LetterListTextView.java

diff --git a/aconfig/launcher.aconfig b/aconfig/launcher.aconfig
index 0df6c368ba..be8ebbbdfc 100644
--- a/aconfig/launcher.aconfig
+++ b/aconfig/launcher.aconfig
@@ -332,3 +332,10 @@ flag {
       purpose: PURPOSE_BUGFIX
     }
 }
+
+flag {
+    name: "letter_fast_scroller"
+    namespace: "launcher"
+    description: "Change fast scroller to a lettered list"
+    bug: "358673724"
+}
diff --git a/res/drawable/bg_letter_list_text.xml b/res/drawable/bg_letter_list_text.xml
new file mode 100644
index 0000000000..427702b045
--- /dev/null
+++ b/res/drawable/bg_letter_list_text.xml
@@ -0,0 +1,23 @@
+<?xml version="1.0" encoding="utf-8"?><!--
+  ~ Copyright (C) 2024 The Android Open Source Project
+  ~
+  ~ Licensed under the Apache License, Version 2.0 (the "License");
+  ~ you may not use this file except in compliance with the License.
+  ~ You may obtain a copy of the License at
+  ~
+  ~      http://www.apache.org/licenses/LICENSE-2.0
+  ~
+  ~ Unless required by applicable law or agreed to in writing, software
+  ~ distributed under the License is distributed on an "AS IS" BASIS,
+  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  ~ See the License for the specific language governing permissions and
+  ~ limitations under the License.
+  -->
+<shape xmlns:android="http://schemas.android.com/apk/res/android"
+    android:shape="oval">
+    <solid android:color="?attr/materialColorSurfaceContainer" />
+    <corners android:radius="100dp"/>
+    <size
+        android:width="@dimen/bg_letter_list_text_size"
+        android:height="@dimen/bg_letter_list_text_size"/>
+</shape>
\ No newline at end of file
diff --git a/res/layout/all_apps_fast_scroller.xml b/res/layout/all_apps_fast_scroller.xml
index 0f1d9330a6..7e16ca5c0b 100644
--- a/res/layout/all_apps_fast_scroller.xml
+++ b/res/layout/all_apps_fast_scroller.xml
@@ -36,4 +36,17 @@
         android:layout_marginEnd="@dimen/fastscroll_end_margin"
         launcher:canThumbDetach="true" />
 
+    <androidx.constraintlayout.widget.ConstraintLayout
+        android:id="@+id/scroll_letter_layout"
+        android:layout_width="@dimen/fastscroll_width"
+        android:layout_height="wrap_content"
+        android:orientation="vertical"
+        android:layout_alignParentBottom="true"
+        android:layout_alignParentEnd="true"
+        android:layout_alignTop="@+id/all_apps_header"
+        android:layout_marginTop="@dimen/all_apps_header_bottom_padding"
+        android:layout_marginEnd="@dimen/fastscroll_list_letter_end_margin"
+        android:clipToPadding="false"
+        android:outlineProvider="none"
+        />
 </merge>
\ No newline at end of file
diff --git a/res/layout/fast_scroller_letter_list_text_view.xml b/res/layout/fast_scroller_letter_list_text_view.xml
new file mode 100644
index 0000000000..493b6fcb7e
--- /dev/null
+++ b/res/layout/fast_scroller_letter_list_text_view.xml
@@ -0,0 +1,24 @@
+<?xml version="1.0" encoding="utf-8"?><!--
+  ~ Copyright (C) 2024 The Android Open Source Project
+  ~
+  ~ Licensed under the Apache License, Version 2.0 (the "License");
+  ~ you may not use this file except in compliance with the License.
+  ~ You may obtain a copy of the License at
+  ~
+  ~      http://www.apache.org/licenses/LICENSE-2.0
+  ~
+  ~ Unless required by applicable law or agreed to in writing, software
+  ~ distributed under the License is distributed on an "AS IS" BASIS,
+  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  ~ See the License for the specific language governing permissions and
+  ~ limitations under the License.
+  -->
+
+<com.android.launcher3.allapps.LetterListTextView xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="@dimen/fastscroll_list_letter_size"
+    android:layout_height="@dimen/fastscroll_list_letter_size"
+    android:textSize="@dimen/fastscroll_list_letter_text_size"
+    android:importantForAccessibility="no"
+    android:gravity="center"
+    android:clickable="false">
+</com.android.launcher3.allapps.LetterListTextView>
\ No newline at end of file
diff --git a/res/values/dimens.xml b/res/values/dimens.xml
index 5e1d8a5ad3..39e726803d 100644
--- a/res/values/dimens.xml
+++ b/res/values/dimens.xml
@@ -81,6 +81,11 @@
     <dimen name="fastscroll_popup_text_size">32dp</dimen>
     <dimen name="fastscroll_popup_margin">19dp</dimen>
 
+    <dimen name="fastscroll_list_letter_size">5dp</dimen>
+    <dimen name="fastscroll_list_letter_text_size">14sp</dimen>
+    <dimen name="fastscroll_list_letter_end_margin">-10dp</dimen>
+    <dimen name="bg_letter_list_text_size">20sp</dimen>
+
     <!--
       Fast scroller draws the content horizontally centered. The end of the track should be
       aligned at the end of the container.
diff --git a/src/com/android/launcher3/FastScrollRecyclerView.java b/src/com/android/launcher3/FastScrollRecyclerView.java
index de1748b911..6622e1157f 100644
--- a/src/com/android/launcher3/FastScrollRecyclerView.java
+++ b/src/com/android/launcher3/FastScrollRecyclerView.java
@@ -25,6 +25,7 @@ import android.view.View;
 import android.view.accessibility.AccessibilityNodeInfo;
 
 import androidx.annotation.Nullable;
+import androidx.constraintlayout.widget.ConstraintLayout;
 import androidx.recyclerview.widget.RecyclerView;
 
 import com.android.launcher3.compat.AccessibilityManagerCompat;
@@ -54,9 +55,11 @@ public abstract class FastScrollRecyclerView extends RecyclerView  {
         super(context, attrs, defStyleAttr);
     }
 
-    public void bindFastScrollbar(RecyclerViewFastScroller scrollbar) {
+    public void bindFastScrollbar(RecyclerViewFastScroller scrollbar,
+            RecyclerViewFastScroller.FastScrollerLocation location) {
         mScrollbar = scrollbar;
         mScrollbar.setRecyclerView(this);
+        mScrollbar.setFastScrollerLocation(location);
         onUpdateScrollbar(0);
     }
 
@@ -162,6 +165,13 @@ public abstract class FastScrollRecyclerView extends RecyclerView  {
      */
     public abstract void onUpdateScrollbar(int dy);
 
+    /**
+     * Return the fast scroll letter list view in the A-Z list.
+     */
+    public ConstraintLayout getLetterList() {
+        return null;
+    }
+
     /**
      * <p>Override in each subclass of this base class.
      */
diff --git a/src/com/android/launcher3/allapps/ActivityAllAppsContainerView.java b/src/com/android/launcher3/allapps/ActivityAllAppsContainerView.java
index ad660d22ba..977e934d03 100644
--- a/src/com/android/launcher3/allapps/ActivityAllAppsContainerView.java
+++ b/src/com/android/launcher3/allapps/ActivityAllAppsContainerView.java
@@ -28,6 +28,7 @@ import static com.android.launcher3.logging.StatsLogManager.LauncherEvent.LAUNCH
 import static com.android.launcher3.logging.StatsLogManager.LauncherEvent.LAUNCHER_ALLAPPS_TAP_ON_WORK_TAB;
 import static com.android.launcher3.util.Executors.MAIN_EXECUTOR;
 import static com.android.launcher3.util.ScrollableLayoutManager.PREDICTIVE_BACK_MIN_SCALE;
+import static com.android.launcher3.views.RecyclerViewFastScroller.FastScrollerLocation.ALL_APPS_SCROLLER;
 
 import android.animation.Animator;
 import android.animation.AnimatorListenerAdapter;
@@ -64,6 +65,7 @@ import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.annotation.Px;
 import androidx.annotation.VisibleForTesting;
+import androidx.constraintlayout.widget.ConstraintLayout;
 import androidx.core.graphics.ColorUtils;
 import androidx.recyclerview.widget.RecyclerView;
 
@@ -167,6 +169,7 @@ public class ActivityAllAppsContainerView<T extends Context & ActivityContext>
     protected FloatingHeaderView mHeader;
     protected View mBottomSheetBackground;
     protected RecyclerViewFastScroller mFastScroller;
+    private ConstraintLayout mFastScrollLetterLayout;
 
     /**
      * View that defines the search box. Result is rendered inside {@link #mSearchRecyclerView}.
@@ -281,6 +284,13 @@ public class ActivityAllAppsContainerView<T extends Context & ActivityContext>
         mSearchRecyclerView = findViewById(R.id.search_results_list_view);
         mFastScroller = findViewById(R.id.fast_scroller);
         mFastScroller.setPopupView(findViewById(R.id.fast_scroller_popup));
+        mFastScrollLetterLayout = findViewById(R.id.scroll_letter_layout);
+        if (Flags.letterFastScroller()) {
+            // Set clip children to false otherwise the scroller letters will be clipped.
+            setClipChildren(false);
+        } else {
+            setClipChildren(true);
+        }
 
         mSearchContainer = inflateSearchBar();
         if (!isSearchBarFloating()) {
@@ -562,7 +572,8 @@ public class ActivityAllAppsContainerView<T extends Context & ActivityContext>
             mActivityContext.hideKeyboard();
         }
         if (mAH.get(currentActivePage).mRecyclerView != null) {
-            mAH.get(currentActivePage).mRecyclerView.bindFastScrollbar(mFastScroller);
+            mAH.get(currentActivePage).mRecyclerView.bindFastScrollbar(mFastScroller,
+                    ALL_APPS_SCROLLER);
         }
         // Header keeps track of active recycler view to properly render header protection.
         mHeader.setActiveRV(currentActivePage);
@@ -1495,6 +1506,10 @@ public class ActivityAllAppsContainerView<T extends Context & ActivityContext>
         }
     }
 
+    ConstraintLayout getFastScrollerLetterList() {
+        return mFastScrollLetterLayout;
+    }
+
     /**
      * redraws header protection
      */
@@ -1562,7 +1577,7 @@ public class ActivityAllAppsContainerView<T extends Context & ActivityContext>
         void setup(@NonNull View rv, @Nullable Predicate<ItemInfo> matcher) {
             mAppsList.updateItemFilter(matcher);
             mRecyclerView = (AllAppsRecyclerView) rv;
-            mRecyclerView.bindFastScrollbar(mFastScroller);
+            mRecyclerView.bindFastScrollbar(mFastScroller, ALL_APPS_SCROLLER);
             mRecyclerView.setEdgeEffectFactory(createEdgeEffectFactory());
             mRecyclerView.setApps(mAppsList);
             mRecyclerView.setLayoutManager(mLayoutManager);
diff --git a/src/com/android/launcher3/allapps/AllAppsRecyclerView.java b/src/com/android/launcher3/allapps/AllAppsRecyclerView.java
index 2a472227b9..ae45a35328 100644
--- a/src/com/android/launcher3/allapps/AllAppsRecyclerView.java
+++ b/src/com/android/launcher3/allapps/AllAppsRecyclerView.java
@@ -15,6 +15,9 @@
  */
 package com.android.launcher3.allapps;
 
+import static androidx.constraintlayout.widget.ConstraintSet.MATCH_CONSTRAINT;
+import static androidx.constraintlayout.widget.ConstraintSet.WRAP_CONTENT;
+
 import static com.android.launcher3.config.FeatureFlags.ALL_APPS_GONE_VISIBILITY;
 import static com.android.launcher3.config.FeatureFlags.ENABLE_ALL_APPS_RV_PREINFLATION;
 import static com.android.launcher3.logger.LauncherAtom.ContainerInfo;
@@ -36,22 +39,29 @@ import android.content.Context;
 import android.graphics.Canvas;
 import android.util.AttributeSet;
 import android.util.Log;
+import android.view.LayoutInflater;
 import android.view.View;
+import android.widget.TextView;
 
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
+import androidx.constraintlayout.widget.ConstraintLayout;
+import androidx.constraintlayout.widget.ConstraintSet;
 import androidx.core.util.Consumer;
 import androidx.recyclerview.widget.RecyclerView;
 
 import com.android.launcher3.DeviceProfile;
 import com.android.launcher3.ExtendedEditText;
 import com.android.launcher3.FastScrollRecyclerView;
+import com.android.launcher3.Flags;
 import com.android.launcher3.LauncherAppState;
 import com.android.launcher3.R;
 import com.android.launcher3.Utilities;
 import com.android.launcher3.logging.StatsLogManager;
 import com.android.launcher3.views.ActivityContext;
 
+import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 
 /**
@@ -66,6 +76,7 @@ public class AllAppsRecyclerView extends FastScrollRecyclerView {
     protected final int mNumAppsPerRow;
     private final AllAppsFastScrollHelper mFastScrollHelper;
     private int mCumulativeVerticalScroll;
+    private ConstraintLayout mLetterList;
 
     protected AlphabeticalAppsList<?> mApps;
 
@@ -238,6 +249,9 @@ public class AllAppsRecyclerView extends FastScrollRecyclerView {
             return;
         }
 
+        if (Flags.letterFastScroller() && !mScrollbar.isDraggingThumb()) {
+            setLettersToScrollLayout(mApps.getFastScrollerSections());
+        }
         // Only show the scrollbar if there is height to be scrolled
         int availableScrollBarHeight = getAvailableScrollBarHeight();
         int availableScrollHeight = getAvailableScrollHeight();
@@ -319,6 +333,80 @@ public class AllAppsRecyclerView extends FastScrollRecyclerView {
         return false;
     }
 
+    public void setLettersToScrollLayout(
+            List<AlphabeticalAppsList.FastScrollSectionInfo> fastScrollSections) {
+        if (mLetterList != null) {
+            mLetterList.removeAllViews();
+        }
+        Context context = getContext();
+        ActivityAllAppsContainerView<?> allAppsContainerView =
+                ActivityContext.lookupContext(context).getAppsView();
+        mLetterList = allAppsContainerView.getFastScrollerLetterList();
+        mLetterList.setPadding(0, getScrollBarTop(), 0, getScrollBarMarginBottom());
+        List<LetterListTextView> textViews = new ArrayList<>();
+        for (int i = 0; i < fastScrollSections.size(); i++) {
+            AlphabeticalAppsList.FastScrollSectionInfo sectionInfo = fastScrollSections.get(i);
+            LetterListTextView textView =
+                    (LetterListTextView) LayoutInflater.from(context).inflate(
+                            R.layout.fast_scroller_letter_list_text_view, mLetterList, false);
+            int viewId = View.generateViewId();
+            textView.setId(viewId);
+            sectionInfo.setId(viewId);
+            textView.setText(sectionInfo.sectionName);
+            if (i == fastScrollSections.size() - 1) {
+                // The last section info is just a duplicate so that user can scroll to the bottom.
+                textView.setVisibility(INVISIBLE);
+            }
+            ConstraintLayout.LayoutParams lp = new ConstraintLayout.LayoutParams(
+                    MATCH_CONSTRAINT, WRAP_CONTENT);
+            lp.dimensionRatio = "v,1:1";
+            textView.setLayoutParams(lp);
+            textViews.add(textView);
+            mLetterList.addView(textView);
+        }
+        // Need to add an extra textview to be aligned.
+        LetterListTextView lastLetterListTextView = new LetterListTextView(context);
+        int currentId = View.generateViewId();
+        lastLetterListTextView.setId(currentId);
+        lastLetterListTextView.setVisibility(INVISIBLE);
+        textViews.add(lastLetterListTextView);
+        mLetterList.addView(lastLetterListTextView);
+        constraintTextViewsVertically(mLetterList, textViews);
+        mLetterList.setVisibility(VISIBLE);
+    }
+
+    private void constraintTextViewsVertically(ConstraintLayout constraintLayout,
+            List<LetterListTextView> textViews) {
+        ConstraintSet chain = new ConstraintSet();
+        chain.clone(constraintLayout);
+        for (int i = 0; i < textViews.size(); i++) {
+            LetterListTextView currentView = textViews.get(i);
+            if (i == 0) {
+                chain.connect(currentView.getId(), ConstraintSet.TOP, ConstraintSet.PARENT_ID,
+                        ConstraintSet.TOP);
+            } else {
+                chain.connect(currentView.getId(), ConstraintSet.TOP, textViews.get(i-1).getId(),
+                        ConstraintSet.BOTTOM);
+            }
+            chain.connect(currentView.getId(), ConstraintSet.START, constraintLayout.getId(),
+                    ConstraintSet.START);
+            chain.connect(currentView.getId(), ConstraintSet.END, constraintLayout.getId(),
+                    ConstraintSet.END);
+        }
+        int[] viewIds = textViews.stream().mapToInt(TextView::getId).toArray();
+        float[] weights = new float[textViews.size()];
+        Arrays.fill(weights,1); // fill with 1 for equal weights
+        chain.createVerticalChain(constraintLayout.getId(), ConstraintSet.TOP,
+                constraintLayout.getId(), ConstraintSet.BOTTOM, viewIds, weights,
+                ConstraintSet.CHAIN_SPREAD);
+        chain.applyTo(constraintLayout);
+    }
+
+    @Override
+    public ConstraintLayout getLetterList() {
+        return mLetterList;
+    }
+
     private void logCumulativeVerticalScroll() {
         ActivityContext context = ActivityContext.lookupContext(getContext());
         StatsLogManager mgr = context.getStatsLogManager();
diff --git a/src/com/android/launcher3/allapps/AlphabeticalAppsList.java b/src/com/android/launcher3/allapps/AlphabeticalAppsList.java
index a3cabc283f..50b18ce788 100644
--- a/src/com/android/launcher3/allapps/AlphabeticalAppsList.java
+++ b/src/com/android/launcher3/allapps/AlphabeticalAppsList.java
@@ -72,11 +72,17 @@ public class AlphabeticalAppsList<T extends Context & ActivityContext> implement
         public final CharSequence sectionName;
         // The item position
         public final int position;
+        // The view id associated with this section
+        public int id = -1;
 
         public FastScrollSectionInfo(CharSequence sectionName, int position) {
             this.sectionName = sectionName;
             this.position = position;
         }
+
+        public void setId(int id) {
+            this.id = id;
+        }
     }
 
 
diff --git a/src/com/android/launcher3/allapps/LetterListTextView.java b/src/com/android/launcher3/allapps/LetterListTextView.java
new file mode 100644
index 0000000000..9326d79f18
--- /dev/null
+++ b/src/com/android/launcher3/allapps/LetterListTextView.java
@@ -0,0 +1,133 @@
+/*
+ * Copyright (C) 2024 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.launcher3.allapps;
+
+import android.content.Context;
+import android.graphics.PorterDuff;
+import android.graphics.PorterDuffColorFilter;
+import android.graphics.drawable.Drawable;
+import android.util.AttributeSet;
+import android.widget.TextView;
+
+import androidx.core.graphics.ColorUtils;
+
+import com.android.launcher3.R;
+import com.android.launcher3.Utilities;
+import com.android.launcher3.util.Themes;
+
+/**
+ * A TextView that is used to display the letter list in the fast scroller.
+ */
+public class LetterListTextView extends TextView {
+    private static final float ABSOLUTE_TRANSLATION_X = 30f;
+    private static final float ABSOLUTE_SCALE = 1.4f;
+    private final Drawable mLetterBackground;
+    private final int mLetterListTextWidthAndHeight;
+    private final int mTextColor;
+    private final int mBackgroundColor;
+    private final int mSelectedColor;
+
+    public LetterListTextView(Context context) {
+        this(context, null, 0);
+    }
+
+    public LetterListTextView(Context context, AttributeSet attrs) {
+        this(context, attrs, 0);
+    }
+
+    public LetterListTextView(Context context, AttributeSet attrs, int defStyle) {
+        super(context, attrs, defStyle);
+        mLetterBackground = context.getDrawable(R.drawable.bg_letter_list_text);
+        mLetterListTextWidthAndHeight = context.getResources().getDimensionPixelSize(
+                R.dimen.fastscroll_list_letter_size);
+        mTextColor = Themes.getAttrColor(context, R.attr.materialColorOnSurface);
+        mBackgroundColor = Themes.getAttrColor(context, R.attr.materialColorSurfaceContainer);
+        mSelectedColor = Themes.getAttrColor(context, R.attr.materialColorOnSecondary);
+    }
+
+    @Override
+    public void onFinishInflate() {
+        super.onFinishInflate();
+        setBackground(mLetterBackground);
+        setTextColor(mTextColor);
+        setClickable(false);
+        setWidth(mLetterListTextWidthAndHeight);
+        setTextSize(mLetterListTextWidthAndHeight);
+        setVisibility(VISIBLE);
+    }
+
+    /**
+     * Animates the letter list text view based on the current finger position.
+     *
+     * @param currentFingerY The Y position of where the finger is placed on the fastScroller in
+     *                       pixels.
+     */
+    public void animateBasedOnYPosition(int currentFingerY) {
+        if (getBackground() == null) {
+            return;
+        }
+        float cutOffMin = currentFingerY - (getHeight() * 2);
+        float cutOffMax = currentFingerY + (getHeight() * 2);
+        float cutOffDistance = cutOffMax - cutOffMin;
+        // Update the background blend color
+        boolean isWithinAnimationBounds = getY() < cutOffMax && getY() > cutOffMin;
+        if (isWithinAnimationBounds) {
+            getBackground().setColorFilter(new PorterDuffColorFilter(
+                    getBlendColorBasedOnYPosition(currentFingerY, cutOffDistance),
+                    PorterDuff.Mode.MULTIPLY));
+        } else {
+            getBackground().setColorFilter(new PorterDuffColorFilter(
+                    mBackgroundColor, PorterDuff.Mode.MULTIPLY));
+        }
+        translateBasedOnYPosition(currentFingerY, cutOffDistance, isWithinAnimationBounds);
+        scaleBasedOnYPosition(currentFingerY, cutOffDistance, isWithinAnimationBounds);
+    }
+
+    private int getBlendColorBasedOnYPosition(int y, float cutOffDistance) {
+        float raisedCosineBlend = (float) Math.cos(((y - getY()) / (cutOffDistance)) * Math.PI);
+        float blendRatio = Utilities.boundToRange(raisedCosineBlend, 0f, 1f);
+        return ColorUtils.blendARGB(mBackgroundColor, mSelectedColor, blendRatio);
+    }
+
+    private void scaleBasedOnYPosition(int y, float cutOffDistance,
+            boolean isWithinAnimationBounds) {
+        float raisedCosineScale = (float) Math.cos(((y - getY()) / (cutOffDistance)) * Math.PI)
+                * ABSOLUTE_SCALE;
+        if (isWithinAnimationBounds) {
+            raisedCosineScale = Utilities.boundToRange(raisedCosineScale, 1f, ABSOLUTE_SCALE);
+            setScaleX(raisedCosineScale);
+            setScaleY(raisedCosineScale);
+        } else {
+            setScaleX(1);
+            setScaleY(1);
+        }
+    }
+
+    private void translateBasedOnYPosition(int y, float cutOffDistance,
+            boolean isWithinAnimationBounds) {
+        float raisedCosineTranslation =
+                (float) Math.cos(((y - getY()) / (cutOffDistance)) * Math.PI)
+                        * ABSOLUTE_TRANSLATION_X;
+        if (isWithinAnimationBounds) {
+            raisedCosineTranslation = -1 * Utilities.boundToRange(raisedCosineTranslation,
+                    0, ABSOLUTE_TRANSLATION_X);
+            setTranslationX(raisedCosineTranslation);
+        } else {
+            setTranslationX(0);
+        }
+    }
+}
diff --git a/src/com/android/launcher3/views/RecyclerViewFastScroller.java b/src/com/android/launcher3/views/RecyclerViewFastScroller.java
index fa17b7bcfe..63648dd348 100644
--- a/src/com/android/launcher3/views/RecyclerViewFastScroller.java
+++ b/src/com/android/launcher3/views/RecyclerViewFastScroller.java
@@ -20,6 +20,9 @@ import static android.view.HapticFeedbackConstants.CLOCK_TICK;
 
 import static androidx.recyclerview.widget.RecyclerView.SCROLL_STATE_IDLE;
 
+import static com.android.launcher3.views.RecyclerViewFastScroller.FastScrollerLocation.ALL_APPS_SCROLLER;
+import static com.android.launcher3.views.RecyclerViewFastScroller.FastScrollerLocation.WIDGET_SCROLLER;
+
 import android.animation.ObjectAnimator;
 import android.content.Context;
 import android.content.res.Resources;
@@ -40,11 +43,15 @@ import android.view.ViewConfiguration;
 import android.view.WindowInsets;
 import android.widget.TextView;
 
+import androidx.annotation.NonNull;
+import androidx.constraintlayout.widget.ConstraintLayout;
 import androidx.recyclerview.widget.RecyclerView;
 
 import com.android.launcher3.FastScrollRecyclerView;
+import com.android.launcher3.Flags;
 import com.android.launcher3.R;
 import com.android.launcher3.Utilities;
+import com.android.launcher3.allapps.LetterListTextView;
 import com.android.launcher3.graphics.FastScrollThumbDrawable;
 import com.android.launcher3.util.Themes;
 
@@ -55,6 +62,19 @@ import java.util.List;
  * The track and scrollbar that shows when you scroll the list.
  */
 public class RecyclerViewFastScroller extends View {
+
+    /** FastScrollerLocation describes what RecyclerView the fast scroller is dedicated to. */
+    public enum FastScrollerLocation {
+        UNKNOWN_SCROLLER(0),
+        ALL_APPS_SCROLLER(1),
+        WIDGET_SCROLLER(2);
+
+        public final int location;
+
+        FastScrollerLocation(int location) {
+            this.location = location;
+        }
+    }
     private static final String TAG = "RecyclerViewFastScroller";
     private static final boolean DEBUG = false;
     private static final int FASTSCROLL_THRESHOLD_MILLIS = 40;
@@ -106,6 +126,8 @@ public class RecyclerViewFastScroller extends View {
     private final Point mThumbDrawOffset = new Point();
 
     private final Paint mTrackPaint;
+    private final int mThumbColor;
+    private final int mThumbLetterScrollerColor;
 
     private float mLastTouchY;
     private boolean mIsDragging;
@@ -139,6 +161,7 @@ public class RecyclerViewFastScroller extends View {
     private int mDownX;
     private int mDownY;
     private int mLastY;
+    private FastScrollerLocation mFastScrollerLocation;
 
     public RecyclerViewFastScroller(Context context) {
         this(context, null);
@@ -151,13 +174,16 @@ public class RecyclerViewFastScroller extends View {
     public RecyclerViewFastScroller(Context context, AttributeSet attrs, int defStyleAttr) {
         super(context, attrs, defStyleAttr);
 
+        mFastScrollerLocation = FastScrollerLocation.UNKNOWN_SCROLLER;
         mTrackPaint = new Paint();
         mTrackPaint.setColor(Themes.getAttrColor(context, android.R.attr.textColorPrimary));
         mTrackPaint.setAlpha(MAX_TRACK_ALPHA);
 
+        mThumbColor = Themes.getColorAccent(context);
+        mThumbLetterScrollerColor = Themes.getAttrColor(context, R.attr.materialColorSurfaceBright);
         mThumbPaint = new Paint();
         mThumbPaint.setAntiAlias(true);
-        mThumbPaint.setColor(Themes.getColorAccent(context));
+        mThumbPaint.setColor(mThumbColor);
         mThumbPaint.setStyle(Paint.Style.FILL);
 
         Resources res = getResources();
@@ -334,6 +360,18 @@ public class RecyclerViewFastScroller extends View {
         animatePopupVisibility(!TextUtils.isEmpty(sectionName));
         mLastTouchY = boundedY;
         setThumbOffsetY((int) mLastTouchY);
+        updateFastScrollerLetterList(y);
+    }
+
+    private void updateFastScrollerLetterList(int y) {
+        if (!shouldUseLetterFastScroller()) {
+            return;
+        }
+        ConstraintLayout mLetterList = mRv.getLetterList();
+        for (int i = 0; i < mLetterList.getChildCount(); i++) {
+            LetterListTextView currentLetter = (LetterListTextView) mLetterList.getChildAt(i);
+            currentLetter.animateBasedOnYPosition(y + mTouchOffsetY);
+        }
     }
 
     /** End any active fast scrolling touch handling, if applicable. */
@@ -359,15 +397,35 @@ public class RecyclerViewFastScroller extends View {
         mThumbDrawOffset.set(getWidth() / 2, mRv.getScrollBarTop());
         // Draw the track
         float halfW = mWidth / 2;
-        canvas.drawRoundRect(-halfW, 0, halfW, mRv.getScrollbarTrackHeight(),
-                mWidth, mWidth, mTrackPaint);
-
-        canvas.translate(0, mThumbOffsetY);
+        boolean useLetterFastScroller = shouldUseLetterFastScroller();
+        if (useLetterFastScroller) {
+            float translateX;
+            if (mIsDragging) {
+                // halfW * 3 is half circle.
+                translateX = halfW * 3;
+            } else {
+                translateX = halfW * 5;
+            }
+            canvas.translate(translateX, mThumbOffsetY);
+        } else {
+            canvas.drawRoundRect(-halfW, 0, halfW, mRv.getScrollbarTrackHeight(),
+                    mWidth, mWidth, mTrackPaint);
+            canvas.translate(0, mThumbOffsetY);
+        }
         mThumbDrawOffset.y += mThumbOffsetY;
+
+        /* Draw half circle */
         halfW += mThumbPadding;
         float r = getScrollThumbRadius();
-        mThumbBounds.set(-halfW, 0, halfW, mThumbHeight);
-        canvas.drawRoundRect(mThumbBounds, r, r, mThumbPaint);
+        if (useLetterFastScroller) {
+            mThumbPaint.setColor(mThumbLetterScrollerColor);
+            mThumbBounds.set(0, 0, 0, mThumbHeight);
+            canvas.drawCircle(-halfW, halfW, r * 2, mThumbPaint);
+        } else {
+            mThumbPaint.setColor(mThumbColor);
+            mThumbBounds.set(-halfW, 0, halfW, mThumbHeight);
+            canvas.drawRoundRect(mThumbBounds, r, r, mThumbPaint);
+        }
         mThumbBounds.roundOut(SYSTEM_GESTURE_EXCLUSION_RECT.get(0));
         // swiping very close to the thumb area (not just within it's bound)
         // will also prevent back gesture
@@ -380,6 +438,11 @@ public class RecyclerViewFastScroller extends View {
         canvas.restoreToCount(saveCount);
     }
 
+    boolean shouldUseLetterFastScroller() {
+        return Flags.letterFastScroller()
+                && getScrollerLocation() == FastScrollerLocation.ALL_APPS_SCROLLER;
+    }
+
     @Override
     public WindowInsets onApplyWindowInsets(WindowInsets insets) {
         mSystemGestureInsets = insets.getSystemGestureInsets();
@@ -421,19 +484,25 @@ public class RecyclerViewFastScroller extends View {
         return isNearThumb(x, y);
     }
 
-    /**
-     * Returns whether the specified x position is near the scroll bar.
-     */
-    public boolean isNearScrollBar(int x) {
-        return x >= (getWidth() - mMaxWidth) / 2 - mScrollbarLeftOffsetTouchDelegate
-                && x <= (getWidth() + mMaxWidth) / 2;
+    public FastScrollerLocation getScrollerLocation() {
+        return mFastScrollerLocation;
+    }
+
+    public void setFastScrollerLocation(@NonNull FastScrollerLocation location) {
+        mFastScrollerLocation = location;
     }
 
     private void animatePopupVisibility(boolean visible) {
         if (mPopupVisible != visible) {
             mPopupVisible = visible;
-            mPopupView.animate().cancel();
-            mPopupView.animate().alpha(visible ? 1f : 0f).setDuration(visible ? 200 : 150).start();
+            if (shouldUseLetterFastScroller()) {
+                mRv.getLetterList().animate().alpha(visible ? 1f : 0f)
+                        .setDuration(visible ? 200 : 150).start();
+            } else {
+                mPopupView.animate().cancel();
+                mPopupView.animate().alpha(visible ? 1f : 0f)
+                        .setDuration(visible ? 200 : 150).start();
+            }
         }
     }
 
diff --git a/src/com/android/launcher3/widget/picker/WidgetsFullSheet.java b/src/com/android/launcher3/widget/picker/WidgetsFullSheet.java
index 2af8e6fd94..caca34fac6 100644
--- a/src/com/android/launcher3/widget/picker/WidgetsFullSheet.java
+++ b/src/com/android/launcher3/widget/picker/WidgetsFullSheet.java
@@ -20,6 +20,7 @@ import static com.android.launcher3.Flags.enableUnfoldedTwoPanePicker;
 import static com.android.launcher3.allapps.ActivityAllAppsContainerView.AdapterHolder.SEARCH;
 import static com.android.launcher3.logging.StatsLogManager.LauncherEvent.LAUNCHER_WIDGETSTRAY_SEARCHED;
 import static com.android.launcher3.testing.shared.TestProtocol.NORMAL_STATE_ORDINAL;
+import static com.android.launcher3.views.RecyclerViewFastScroller.FastScrollerLocation.WIDGET_SCROLLER;
 
 import android.animation.Animator;
 import android.content.Context;
@@ -119,7 +120,7 @@ public class WidgetsFullSheet extends BaseWidgetSheet
                     WidgetsRecyclerView searchRecyclerView =
                             mAdapters.get(AdapterHolder.SEARCH).mWidgetsRecyclerView;
                     if (mIsInSearchMode && searchRecyclerView != null) {
-                        searchRecyclerView.bindFastScrollbar(mFastScroller);
+                        searchRecyclerView.bindFastScrollbar(mFastScroller, WIDGET_SCROLLER);
                     }
                 }
 
@@ -276,7 +277,7 @@ public class WidgetsFullSheet extends BaseWidgetSheet
     }
 
     private void attachScrollbarToRecyclerView(WidgetsRecyclerView recyclerView) {
-        recyclerView.bindFastScrollbar(mFastScroller);
+        recyclerView.bindFastScrollbar(mFastScroller, WIDGET_SCROLLER);
         if (mCurrentWidgetsRecyclerView != recyclerView) {
             // Only reset the scroll position & expanded apps if the currently shown recycler view
             // has been updated.
@@ -1057,7 +1058,7 @@ public class WidgetsFullSheet extends BaseWidgetSheet
             mWidgetsRecyclerView.setClipToOutline(true);
             mWidgetsRecyclerView.setClipChildren(false);
             mWidgetsRecyclerView.setAdapter(mWidgetsListAdapter);
-            mWidgetsRecyclerView.bindFastScrollbar(mFastScroller);
+            mWidgetsRecyclerView.bindFastScrollbar(mFastScroller, WIDGET_SCROLLER);
             mWidgetsRecyclerView.setItemAnimator(isTwoPane() ? null : mWidgetsListItemAnimator);
             mWidgetsRecyclerView.setHeaderViewDimensionsProvider(WidgetsFullSheet.this);
             if (!isTwoPane()) {