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Commit 61a243a3 authored by Prabir Pradhan's avatar Prabir Pradhan
Browse files

Treat Bluetooth-smoothened events with modified timestmaps as synthetic 

Since we are modifying the timestamps of events from Bluetooth devices,
these may have unintended consequences on latency metrics. Treat these
modified events as synthetic by setting the event time equal to the read
time to give it zero read latency.

Bug: 257124950
Test: atest inputflinger_tests
Change-Id: I65288050b273e6544861af1db0aee7a42d1b246d
parent 0e33fae8

services/inputflinger/reader/mapper/CursorInputMapper.cpp

+4 −3
Original line number Diff line number Diff line
@@ -300,10 +300,11 @@ std::list<NotifyArgs> CursorInputMapper::process(const RawEvent* rawEvent) { 
    mCursorScrollAccumulator.process(rawEvent);



    if (rawEvent->type == EV_SYN && rawEvent->code == SYN_REPORT) {

        const nsecs_t eventTime =

        const auto [eventTime, readTime] =

                applyBluetoothTimestampSmoothening(getDeviceContext().getDeviceIdentifier(),

                                                   rawEvent->when, mLastEventTime);

        out += sync(eventTime, rawEvent->readTime);

                                                   rawEvent->when, rawEvent->readTime,

                                                   mLastEventTime);

        out += sync(eventTime, readTime);

        mLastEventTime = eventTime;

    }

    return out;

services/inputflinger/reader/mapper/TouchCursorInputMapperCommon.h

+12 −5
Original line number Diff line number Diff line
@@ -110,10 +110,11 @@ static bool isPointerDown(int32_t buttonState) { 
// coordinates result in extremely large instantaneous velocities, which can negatively impact

// user experience. To avoid this, we augment the timestamps so that subsequent event timestamps

// differ by at least a minimum delta value.

static nsecs_t applyBluetoothTimestampSmoothening(const InputDeviceIdentifier& identifier,

                                                  nsecs_t currentEventTime, nsecs_t lastEventTime) {

static std::tuple<nsecs_t /*eventTime*/, nsecs_t /*readTime*/> applyBluetoothTimestampSmoothening(

        const InputDeviceIdentifier& identifier, nsecs_t currentEventTime, nsecs_t readTime,

        nsecs_t lastEventTime) {

    if (identifier.bus != BUS_BLUETOOTH) {

        return currentEventTime;

        return {currentEventTime, readTime};

    }



    // Assume the fastest rate at which a Bluetooth touch device can report input events is one
@@ -123,8 +124,14 @@ static nsecs_t applyBluetoothTimestampSmoothening(const InputDeviceIdentifier& i 
    // We define a maximum smoothing time delta so that we don't generate events too far into the

    // future.

    constexpr static nsecs_t MAX_BLUETOOTH_SMOOTHING_DELTA = ms2ns(32);

    return std::min(std::max(currentEventTime, lastEventTime + MIN_BLUETOOTH_TIMESTAMP_DELTA),

    const nsecs_t smoothenedEventTime =

            std::min(std::max(currentEventTime, lastEventTime + MIN_BLUETOOTH_TIMESTAMP_DELTA),

                     currentEventTime + MAX_BLUETOOTH_SMOOTHING_DELTA);

    // If we are modifying the event time, treat this event as a synthetically generated event for

    // latency tracking purposes and use the event time as the read time (zero read latency).

    const nsecs_t smoothenedReadTime =

            smoothenedEventTime != currentEventTime ? currentEventTime : readTime;

    return {smoothenedEventTime, smoothenedReadTime};

}



} // namespace android

services/inputflinger/reader/mapper/TouchInputMapper.cpp

+3 −2
Original line number Diff line number Diff line
@@ -1467,8 +1467,9 @@ std::list<NotifyArgs> TouchInputMapper::sync(nsecs_t when, nsecs_t readTime) { 
    const RawState& last =

            mRawStatesPending.size() == 1 ? mCurrentRawState : mRawStatesPending.rbegin()[1];



    next.when = applyBluetoothTimestampSmoothening(getDeviceContext().getDeviceIdentifier(), when,

                                                   last.when);

    std::tie(next.when, next.readTime) =

            applyBluetoothTimestampSmoothening(getDeviceContext().getDeviceIdentifier(), when,

                                               readTime, last.when);



    // Assign pointer ids.

    if (!mHavePointerIds) {