commit 346ac6a5fa15cc2d36a7b4cb2985bfc68ec37655
author Siarhei Vishniakou <svv@google.com> Wed Apr 10 09:58:05 2019 -0700
committer Siarhei Vishniakou <svv@google.com> Mon Apr 15 14:00:26 2019 -0700
tree 67310dda2416d63d5453763bbf0b8721ef0a4227
parent 651c1ea988ba9a49b2715bd289f7cacda0f81d54

Prevent entries with identical times

Currently, VelocityTracker adds all MotionEvents with actions DOWN,
MOVE, and POINTER_DOWN. But sometimes these events can have identical
timestamps, for example MOVE and the following POINTER_DOWN.

This breaks algorithms that rely on computing differences between
times of the events. If the difference is zero, and division is
performed, then very large numbers can result from this.

Bug: 129797752
Test: atest libinput_tests
Change-Id: I843fd9efbdbf786ab7aa5ed62b4e1395ae7cf335

libs/input/VelocityTracker.cpp

diff --git a/libs/input/VelocityTracker.cpp b/libs/input/VelocityTracker.cpp
index 42d774e..c6cc4fc 100644
--- a/libs/input/VelocityTracker.cpp
+++ b/libs/input/VelocityTracker.cpp
@@ -382,7 +382,16 @@
 
 void LeastSquaresVelocityTrackerStrategy::addMovement(nsecs_t eventTime, BitSet32 idBits,
         const VelocityTracker::Position* positions) {
-    if (++mIndex == HISTORY_SIZE) {
+    if (mMovements[mIndex].eventTime != eventTime) {
+        // When ACTION_POINTER_DOWN happens, we will first receive ACTION_MOVE with the coordinates
+        // of the existing pointers, and then ACTION_POINTER_DOWN with the coordinates that include
+        // the new pointer. If the eventtimes for both events are identical, just update the data
+        // for this time.
+        // We only compare against the last value, as it is likely that addMovement is called
+        // in chronological order as events occur.
+        mIndex++;
+    }
+    if (mIndex == HISTORY_SIZE) {
         mIndex = 0;
     }
 
@@ -1017,7 +1026,16 @@
 
 void ImpulseVelocityTrackerStrategy::addMovement(nsecs_t eventTime, BitSet32 idBits,
         const VelocityTracker::Position* positions) {
-    if (++mIndex == HISTORY_SIZE) {
+    if (mMovements[mIndex].eventTime != eventTime) {
+        // When ACTION_POINTER_DOWN happens, we will first receive ACTION_MOVE with the coordinates
+        // of the existing pointers, and then ACTION_POINTER_DOWN with the coordinates that include
+        // the new pointer. If the eventtimes for both events are identical, just update the data
+        // for this time.
+        // We only compare against the last value, as it is likely that addMovement is called
+        // in chronological order as events occur.
+        mIndex++;
+    }
+    if (mIndex == HISTORY_SIZE) {
         mIndex = 0;
     }