From 2e564400ba6282a8fd12d20f4f8749c7c4e98853 Mon Sep 17 00:00:00 2001
From: Tony Mak <tonymak@google.com>
Date: Tue, 27 Feb 2018 17:19:34 +0000
Subject: [PATCH] Fix all apps tab fling detection

It is a regression when we changed from ViewPager to PagedView.
Unlike ViewPager, PagedView does not take "yDiff" into account
when determining should it intercept its child MotionEvent.

Override determineScrollingStart, just like what we did in Workspace

Change-Id: I25f7415c45c370629558d944f59bf95c741b9319
FIX: 73878167
---
 src/com/android/launcher3/PagedView.java      |  8 +++++
 .../launcher3/allapps/AllAppsPagedView.java   | 33 ++++++++++++++++++-
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/src/com/android/launcher3/PagedView.java b/src/com/android/launcher3/PagedView.java
index ccb0a955d3..4be32b2070 100644
--- a/src/com/android/launcher3/PagedView.java
+++ b/src/com/android/launcher3/PagedView.java
@@ -1892,6 +1892,14 @@ public abstract class PagedView<T extends View & PageIndicator> extends ViewGrou
                 getNextPage() + 1, getChildCount());
     }
 
+    protected float getDownMotionX() {
+        return mDownMotionX;
+    }
+
+    protected float getDownMotionY() {
+        return mDownMotionY;
+    }
+
     @Override
     public boolean onHoverEvent(android.view.MotionEvent event) {
         return true;
diff --git a/src/com/android/launcher3/allapps/AllAppsPagedView.java b/src/com/android/launcher3/allapps/AllAppsPagedView.java
index 86186fdb5a..3b4450bf8a 100644
--- a/src/com/android/launcher3/allapps/AllAppsPagedView.java
+++ b/src/com/android/launcher3/allapps/AllAppsPagedView.java
@@ -18,12 +18,17 @@ package com.android.launcher3.allapps;
 import android.content.Context;
 import android.util.AttributeSet;
 
+import android.view.MotionEvent;
 import com.android.launcher3.PagedView;
 import com.android.launcher3.R;
 
 public class AllAppsPagedView extends PagedView<PersonalWorkSlidingTabStrip> {
 
-    public AllAppsPagedView(Context context) {
+  final static float START_DAMPING_TOUCH_SLOP_ANGLE = (float) Math.PI / 6;
+  final static float MAX_SWIPE_ANGLE = (float) Math.PI / 3;
+  final static float TOUCH_SLOP_DAMPING_FACTOR = 4;
+
+  public AllAppsPagedView(Context context) {
         this(context, null);
     }
 
@@ -46,4 +51,30 @@ public class AllAppsPagedView extends PagedView<PersonalWorkSlidingTabStrip> {
         super.onScrollChanged(l, t, oldl, oldt);
         mPageIndicator.setScroll(l, mMaxScrollX);
     }
+
+    @Override
+    protected void determineScrollingStart(MotionEvent ev) {
+        float absDeltaX = Math.abs(ev.getX() - getDownMotionX());
+        float absDeltaY = Math.abs(ev.getY() - getDownMotionY());
+
+        if (Float.compare(absDeltaX, 0f) == 0) return;
+
+        float slope = absDeltaY / absDeltaX;
+        float theta = (float) Math.atan(slope);
+
+        if (absDeltaX > mTouchSlop || absDeltaY > mTouchSlop) {
+            cancelCurrentPageLongPress();
+        }
+
+        if (theta > MAX_SWIPE_ANGLE) {
+            return;
+        } else if (theta > START_DAMPING_TOUCH_SLOP_ANGLE) {
+            theta -= START_DAMPING_TOUCH_SLOP_ANGLE;
+            float extraRatio = (float)
+                    Math.sqrt((theta / (MAX_SWIPE_ANGLE - START_DAMPING_TOUCH_SLOP_ANGLE)));
+            super.determineScrollingStart(ev, 1 + TOUCH_SLOP_DAMPING_FACTOR * extraRatio);
+        } else {
+            super.determineScrollingStart(ev);
+        }
+    }
 }