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Candidate 1: the rising edge of an authentication sends the touch event only

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Labelled baseline on the proven loop, quick taps only: enrolled finger 2 of 10,
wrong finger 0 of 5. Every press was one frame.

The rising-edge frame costs ~700 ms because it runs the matcher twice -- event 5
and event 7 on the same image, two verdicts back. A human tap is over before a
second frame can exist at that cost. Keeping only the touch event keeps what
every recorded match followed, halves the rising frame, and may be the
difference between one frame per tap and two. It is a single variable against a
labelled baseline; if the rate drops, it comes out.

Also fixes fptrial.sh's latency column, which was all zero: busybox date has no
%N, so it reads /proc/uptime instead.
This commit is contained in:
Jorijn van der Graaf 2026-09-02 23:46:12 +02:00
commit 00925db485
3 changed files with 13 additions and 4 deletions
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11
interfaces/Fingerprintd-Engine.cppm
View file

@ -109,7 +109,16 @@ export namespace fingerprintd::engine {
bool falling = !finger && prev_;
if (rising)
out.push_back(Event::FingerTouched);
if (finger && mode == Mode::Authenticate)
// CANDIDATE 1, under measurement: on the rising edge of an
// authentication, the touch event alone. It does run the matcher
// here (the rising frame answered `MATCH MATCH` / `rej rej` with
// both events -- two verdicts from one image), and every recorded
// match followed a touch event, so this keeps what is known to
// matter and drops ~300 ms of duplicate work on the frame that
// decides every quick tap. Held frames still send image-ready.
// Labelled baseline before this change: 2/10 quick taps matched,
// 0/5 wrong-finger taps. If the rate drops, this comes out.
if (finger && mode == Mode::Authenticate && !rising)
out.push_back(Event::ImageReady);
if (falling)
out.push_back(Event::FingerReleased);

2
packaging/fptrial.sh
View file

@ -9,7 +9,7 @@
# is the latency a user feels. Unlabelled runs cannot be turned into a rate.
C=${1:-10}; W=${2:-5}
OUT=/tmp/fptrial-$(date +%Y%m%d-%H%M%S).log
now() { date +%s%N; }
now() { awk '{gsub(/\./,""); print $1 "0000000"}' /proc/uptime; }
run() { # $1 = label
printf '\n>>> %s -- press and LIFT (quick tap) ... ' "$1"
t0=$(now)

4
tests/Engine/main.cpp
View file

@ -121,8 +121,8 @@ int main() {
// its press. Not to be removed without a measurement isolating it.
TouchTracker a;
auto a1 = a.Observe(true, Mode::Authenticate);
Check(a1.size() == 2 && a1[0] == Event::FingerTouched && a1[1] == Event::ImageReady,
"auth: rising edge reports touched then image-ready");
Check(a1.size() == 1 && a1[0] == Event::FingerTouched,
"auth: rising edge reports touched only (candidate 1: one matcher run)");
auto a2 = a.Observe(true, Mode::Authenticate);
Check(a2.size() == 1 && a2[0] == Event::ImageReady, "auth: a held frame still reports image-ready");
auto a3 = a.Observe(false, Mode::Authenticate);