From 43ee58e49dc5558f8b5bc251240cdb86e75a54b6 Mon Sep 17 00:00:00 2001
From: Dave Mankoff <mankoff@google.com>
Date: Wed, 1 May 2019 16:25:18 -0400
Subject: [PATCH] Limit touch sampling rate for falsing.

Our falsing manager has a hard time with high sample rates. It's tuned
for a predefined rate of 60hz. In this CL, we simply drop extra
samples since they can cause false positives in our falsing.

Bug: 130256776
Test: Manual

Change-Id: I5d4dc239e4185f984f108b92e352e5184c52821a
---
 .../systemui/classifier/ClassifierData.java    | 18 +++++++++++++++++-
 .../classifier/HumanInteractionClassifier.java |  4 +++-
 .../android/systemui/classifier/Stroke.java    |  8 ++++++++
 3 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/packages/SystemUI/src/com/android/systemui/classifier/ClassifierData.java b/packages/SystemUI/src/com/android/systemui/classifier/ClassifierData.java
index c83c74f69f908..95e497e6574cd 100644
--- a/packages/SystemUI/src/com/android/systemui/classifier/ClassifierData.java
+++ b/packages/SystemUI/src/com/android/systemui/classifier/ClassifierData.java
@@ -26,6 +26,9 @@ import java.util.ArrayList;
  * example, provide information on the current touch state.
  */
 public class ClassifierData {
+    private static final long MINIMUM_DT_NANOS = 16666666;  // 60Hz
+    private static final long MINIMUM_DT_SMEAR_NANOS = 2500000;  // 2.5ms
+
     private SparseArray<Stroke> mCurrentStrokes = new SparseArray<>();
     private ArrayList<Stroke> mEndingStrokes = new ArrayList<>();
     private final float mDpi;
@@ -34,7 +37,18 @@ public class ClassifierData {
         mDpi = dpi;
     }
 
-    public void update(MotionEvent event) {
+    /** Returns true if the event should be considered, false otherwise. */
+    public boolean update(MotionEvent event) {
+        // We limit to 60hz sampling. Drop anything happening faster than that.
+        // Legacy code was created with an assumed sampling rate. As devices increase their
+        // sampling rate, this creates potentialy false positives.
+        if (event.getActionMasked() == MotionEvent.ACTION_MOVE
+                && mCurrentStrokes.size() != 0
+                && event.getEventTimeNano() - mCurrentStrokes.get(0).getLastEventTimeNano()
+                        < MINIMUM_DT_NANOS - MINIMUM_DT_SMEAR_NANOS) {
+            return false;
+        }
+
         mEndingStrokes.clear();
         int action = event.getActionMasked();
         if (action == MotionEvent.ACTION_DOWN) {
@@ -54,6 +68,8 @@ public class ClassifierData {
                 mEndingStrokes.add(getStroke(id));
             }
         }
+
+        return true;
     }
 
     public void cleanUp(MotionEvent event) {
diff --git a/packages/SystemUI/src/com/android/systemui/classifier/HumanInteractionClassifier.java b/packages/SystemUI/src/com/android/systemui/classifier/HumanInteractionClassifier.java
index 0cc50cddbfc6c..86dccb2228753 100644
--- a/packages/SystemUI/src/com/android/systemui/classifier/HumanInteractionClassifier.java
+++ b/packages/SystemUI/src/com/android/systemui/classifier/HumanInteractionClassifier.java
@@ -151,7 +151,9 @@ public class HumanInteractionClassifier extends Classifier {
     }
 
     private void addTouchEvent(MotionEvent event) {
-        mClassifierData.update(event);
+        if (!mClassifierData.update(event)) {
+            return;
+        }
 
         for (StrokeClassifier c : mStrokeClassifiers) {
             c.onTouchEvent(event);
diff --git a/packages/SystemUI/src/com/android/systemui/classifier/Stroke.java b/packages/SystemUI/src/com/android/systemui/classifier/Stroke.java
index fb04d3e73a2d9..977a2d0b528a6 100644
--- a/packages/SystemUI/src/com/android/systemui/classifier/Stroke.java
+++ b/packages/SystemUI/src/com/android/systemui/classifier/Stroke.java
@@ -68,4 +68,12 @@ public class Stroke {
     public ArrayList<Point> getPoints() {
         return mPoints;
     }
+
+    public long getLastEventTimeNano() {
+        if (mPoints.isEmpty()) {
+            return mStartTimeNano;
+        }
+
+        return mPoints.get(mPoints.size() - 1).timeOffsetNano;
+    }
 }