From 53463397c3b84bb71d7fe155a8ada86fdcc0e96b Mon Sep 17 00:00:00 2001
From: Paul Ramirez <peramirez@google.com>
Date: Mon, 11 Nov 2024 21:49:51 +0000
Subject: Fix One Euro filter's units of computation

Changed the units that the One Euro filter uses to compute the filtered
coordinates. This was causing a crash because if two timestamps were
sufficiently close to each other, by the time of implicitly converting
from nanoseconds to seconds, they were considered equal. This led to a
zero division when calculating the sampling frequency. Now, everything
is handled in the scale of nanoseconds, and conversion are done if and
only if they're necessary.

Bug: 297226446
Flag: EXEMPT bugfix
Test: TEST=libinput_tests; m $TEST && $ANDROID_HOST_OUT/nativetest64/$TEST/$TEST
Change-Id: I7fced6db447074cccb3d938eb9dc7a9707433f53
---
 include/input/CoordinateFilter.h |  2 +-
 include/input/OneEuroFilter.h    | 10 +++++-----
 2 files changed, 6 insertions(+), 6 deletions(-)

(limited to 'include')

diff --git a/include/input/CoordinateFilter.h b/include/input/CoordinateFilter.h
index f36472dc8c..8f2e605e85 100644
--- a/include/input/CoordinateFilter.h
+++ b/include/input/CoordinateFilter.h
@@ -44,7 +44,7 @@ public:
      * the previous call.
      * @param coords Coordinates to be overwritten by the corresponding filtered coordinates.
      */
-    void filter(std::chrono::duration<float> timestamp, PointerCoords& coords);
+    void filter(std::chrono::nanoseconds timestamp, PointerCoords& coords);
 
 private:
     OneEuroFilter mXFilter;
diff --git a/include/input/OneEuroFilter.h b/include/input/OneEuroFilter.h
index a0168e4f91..bdd82b2ee8 100644
--- a/include/input/OneEuroFilter.h
+++ b/include/input/OneEuroFilter.h
@@ -56,7 +56,7 @@ public:
      * provided in the previous call.
      * @param rawPosition Position to be filtered.
      */
-    float filter(std::chrono::duration<float> timestamp, float rawPosition);
+    float filter(std::chrono::nanoseconds timestamp, float rawPosition);
 
 private:
     /**
@@ -67,7 +67,7 @@ private:
 
     /**
      * Slope of the cutoff frequency criterion. This is the term scaling the absolute value of the
-     * filtered signal's speed. The data member is dimensionless, that is, it does not have units.
+     * filtered signal's speed. Units are 1 / position.
      */
     const float mBeta;
 
@@ -78,9 +78,9 @@ private:
     const float mSpeedCutoffFreq;
 
     /**
-     * The timestamp from the previous call. Units are seconds.
+     * The timestamp from the previous call.
      */
-    std::optional<std::chrono::duration<float>> mPrevTimestamp;
+    std::optional<std::chrono::nanoseconds> mPrevTimestamp;
 
     /**
      * The raw position from the previous call.
@@ -88,7 +88,7 @@ private:
     std::optional<float> mPrevRawPosition;
 
     /**
-     * The filtered velocity from the previous call. Units are position per second.
+     * The filtered velocity from the previous call. Units are position per nanosecond.
      */
     std::optional<float> mPrevFilteredVelocity;
 
-- 
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