onPreFling always has zero available Velocity after I stop dragging [288499763]

Obsolete

Bug

Status Update

No update yet.

Description

wb...@gmail.com

created issue #1

Jun 23, 2023 01:23PM

Jetpack Compose version: 1.4.3

Jetpack Compose component(s) used: scrollable LazyVerticalGrid

Android Studio Build: Android Studio Flamingo

Kotlin version: 1.8.21

Steps to Reproduce or Code Sample to Reproduce:

In a LazyVerticalGrid, when scrolling after I stop dragging, no fling animation happens
This happens on a slower Android 7.1.1 device.

LazyVerticalGrid(
            columns = GridCells.Adaptive(minSize = 128.dp),
            verticalArrangement = Arrangement.spacedBy(dimensions.large),
            horizontalArrangement = Arrangement.spacedBy(dimensions.large),
            contentPadding = PaddingValues(top = dimensions.large, bottom = dimensions.large),
            modifier = Modifier.pointerInput(Unit) {
                coroutineScope {
                    awaitEachGesture {
                        while (isActive){
                            awaitPointerEvent(pass = PointerEventPass.Initial).changes.forEach{
                                println("awaitPointerEvent: $it")
                            }
                        }
                    }
                }
            }.nestedScroll(
                object : NestedScrollConnection {
                    override suspend fun onPreFling(available: Velocity): Velocity {
                        println("onPreFling available: $available")
                        return super.onPreFling(available)
                    }
                    override fun onPreScroll(
                        available: Offset,
                        source: NestedScrollSource
                    ): Offset {
                        println("onPreScroll available: $available - $source" )
                        return super.onPreScroll(available, source)
                    }

                    override suspend fun onPostFling(
                        consumed: Velocity,
                        available: Velocity
                    ): Velocity {
                        println("onPostFling available: $available")
                        println("onPostFling consumed: $consumed")
                        return super.onPostFling(consumed, available)
                    }

                    override fun onPostScroll(
                        consumed: Offset,
                        available: Offset,
                        source: NestedScrollSource
                    ): Offset {
                        println("onPostScroll available: $available - $source")
                        println("onPostScroll consumed: $consumed")
                        return super.onPostScroll(consumed, available, source)
                    }

                }
            )
        ) {
            items(list, key = { listItem-> listItem.number }, contentType = { it.javaClass }) { listItem ->

        Text(text=listItem.number.toString())
                }
            }
        }

I tried Compose 1.6alpha01 on an Android 7.1.1 device with the VelocityTrackerAddPointsFix set to true. On that device there is still no Fling present.

Logging from a working device:

awaitPointerEvent: PointerInputChange(id=PointerId(value=9), uptimeMillis=293894052, position=Offset(238.5, 837.8), pressed=true, pressure=1.0, previousUptimeMillis=293894052, previousPosition=Offset(238.5, 837.8), previousPressed=false, isConsumed=false, type=Touch, historical=[],scrollDelta=Offset(0.0, 0.0))
awaitPointerEvent: PointerInputChange(id=PointerId(value=9), uptimeMillis=293894106, position=Offset(261.2, 921.8), pressed=true, pressure=1.0, previousUptimeMillis=293894052, previousPosition=Offset(238.5, 837.8), previousPressed=true, isConsumed=false, type=Touch, historical=[HistoricalChange(uptimeMillis=293894090, position=Offset(245.0, 750.5)), HistoricalChange(uptimeMillis=293894099, position=Offset(253.3, 780.3))],scrollDelta=Offset(0.0, 0.0))
onPreScroll available: Offset(0.0, 60.1) - Drag
onPostScroll available: Offset(0.0, 0.0) - Drag
onPostScroll consumed: Offset(0.0, 60.1)
awaitPointerEvent: PointerInputChange(id=PointerId(value=9), uptimeMillis=293894120, position=Offset(278.8, 987.7), pressed=true, pressure=1.0, previousUptimeMillis=293894106, previousPosition=Offset(261.2, 921.8), previousPressed=true, isConsumed=false, type=Touch, historical=[HistoricalChange(uptimeMillis=293894107, position=Offset(262.8, 814.3)), HistoricalChange(uptimeMillis=293894115, position=Offset(273.8, 852.3))],scrollDelta=Offset(0.0, 0.0))
onPreScroll available: Offset(0.0, 65.9) - Drag
onPostScroll available: Offset(0.0, 0.0) - Drag
onPostScroll consumed: Offset(0.0, 65.9)
awaitPointerEvent: PointerInputChange(id=PointerId(value=9), uptimeMillis=293894143, position=Offset(299.0, 1124.2), pressed=true, pressure=1.0, previousUptimeMillis=293894120, previousPosition=Offset(278.8, 987.7), previousPressed=true, isConsumed=false, type=Touch, historical=[HistoricalChange(uptimeMillis=293894123, position=Offset(281.8, 887.5)), HistoricalChange(uptimeMillis=293894132, position=Offset(289.8, 932.8)), HistoricalChange(uptimeMillis=293894140, position=Offset(297.0, 988.8))],scrollDelta=Offset(0.0, 0.0))
onPreScroll available: Offset(0.0, 136.5) - Drag
onPostScroll available: Offset(0.0, 0.0) - Drag
onPostScroll consumed: Offset(0.0, 136.5)
awaitPointerEvent: PointerInputChange(id=PointerId(value=9), uptimeMillis=293894157, position=Offset(307.5, 1255.0), pressed=true, pressure=1.0, previousUptimeMillis=293894143, previousPosition=Offset(299.0, 1124.2), previousPressed=true, isConsumed=false, type=Touch, historical=[HistoricalChange(uptimeMillis=293894148, position=Offset(303.3, 1058.3))],scrollDelta=Offset(0.0, 0.0))
awaitPointerEvent: PointerInputChange(id=PointerId(value=9), uptimeMillis=293894164, position=Offset(307.5, 1255.0), pressed=false, pressure=1.0, previousUptimeMillis=293894157, previousPosition=Offset(307.5, 1255.0), previousPressed=true, isConsumed=false, type=Touch, historical=[],scrollDelta=Offset(0.0, 0.0))
onPreScroll available: Offset(0.0, 130.8) - Drag
onPostScroll available: Offset(0.0, 0.0) - Drag
onPostScroll consumed: Offset(0.0, 130.8)
onPreFling available: (0.0, 7657.776) px/sec
onPreScroll available: Offset(0.0, 0.1) - Fling
onPostScroll available: Offset(0.0, 0.0) - Fling
onPostScroll consumed: Offset(0.0, 0.1)

...

onPostScroll consumed: Offset(0.0, 22.0)
onPreScroll available: Offset(0.0, 23.2) - Fling
onPostScroll available: Offset(0.0, 23.2) - Fling
onPostScroll consumed: Offset(0.0, 0.0)
onPostFling available: (0.0, 1901.2562) px/sec
onPostFling consumed: (0.0, 5756.5195) px/sec

The logs from the Android 7.1.x device:

awaitPointerEvent: PointerInputChange(id=PointerId(value=0), uptimeMillis=15408289, position=Offset(352.5, 1039.1), pressed=true, pressure=1.0, previousUptimeMillis=15408289, previousPosition=Offset(352.5, 1039.1), previousPressed=false, isConsumed=false, type=Touch, historical=[],scrollDelta=Offset(0.0, 0.0))
awaitPointerEvent: PointerInputChange(id=PointerId(value=0), uptimeMillis=15408307, position=Offset(353.0, 1034.7), pressed=true, pressure=1.0, previousUptimeMillis=15408289, previousPosition=Offset(352.5, 1039.1), previousPressed=true, isConsumed=false, type=Touch, historical=[HistoricalChange(uptimeMillis=15408302, position=Offset(352.5, 990.1))],scrollDelta=Offset(0.0, 0.0))
awaitPointerEvent: PointerInputChange(id=PointerId(value=0), uptimeMillis=15408323, position=Offset(355.5, 1014.6), pressed=true, pressure=1.0, previousUptimeMillis=15408307, previousPosition=Offset(353.0, 1034.7), previousPressed=true, isConsumed=false, type=Touch, historical=[HistoricalChange(uptimeMillis=15408312, position=Offset(353.5, 981.2))],scrollDelta=Offset(0.0, 0.0))
onPreScroll available: Offset(0.0, -9.5) - Drag
onPostScroll available: Offset(0.0, 0.0) - Drag
onPostScroll consumed: Offset(0.0, -9.5)
awaitPointerEvent: PointerInputChange(id=PointerId(value=0), uptimeMillis=15408395, position=Offset(398.4, 692.4), pressed=true, pressure=1.0, previousUptimeMillis=15408323, previousPosition=Offset(355.5, 1014.6), previousPressed=true, isConsumed=false, type=Touch, historical=[HistoricalChange(uptimeMillis=15408323, position=Offset(355.5, 965.2)), HistoricalChange(uptimeMillis=15408341, position=Offset(358.5, 937.2)), HistoricalChange(uptimeMillis=15408362, position=Offset(364.5, 892.2)), HistoricalChange(uptimeMillis=15408364, position=Offset(370.5, 845.3)), HistoricalChange(uptimeMillis=15408371, position=Offset(377.5, 784.3)), HistoricalChange(uptimeMillis=15408393, position=Offset(390.5, 714.4))],scrollDelta=Offset(0.0, 0.0))
onPreScroll available: Offset(0.0, -322.1) - Drag
onPostScroll available: Offset(0.0, 0.0) - Drag
onPostScroll consumed: Offset(0.0, -322.1)
awaitPointerEvent: PointerInputChange(id=PointerId(value=0), uptimeMillis=15408426, position=Offset(403.4, 541.5), pressed=true, pressure=1.0, previousUptimeMillis=15408395, previousPosition=Offset(398.4, 692.4), previousPressed=true, isConsumed=false, type=Touch, historical=[],scrollDelta=Offset(0.0, 0.0))
awaitPointerEvent: PointerInputChange(id=PointerId(value=0), uptimeMillis=15408472, position=Offset(403.4, 541.5), pressed=false, pressure=1.0, previousUptimeMillis=15408426, previousPosition=Offset(403.4, 541.5), previousPressed=true, isConsumed=false, type=Touch, historical=[],scrollDelta=Offset(0.0, 0.0))
onPreScroll available: Offset(0.0, -150.8) - Drag
onPostScroll available: Offset(0.0, 0.0) - Drag
onPostScroll consumed: Offset(0.0, -150.8)
onPreFling available: (0.0, 0.0) px/sec
onPostFling available: (0.0, 0.0) px/sec
onPostFling consumed: (0.0, 0.0) px/sec

After debugging more in the Jetpack Compose I have found the following in androidx.compose.ui.input.pointer.util.VelocityTracker:

private const val AssumePointerMoveStoppedMilliseconds: Int = 40

and in the function calculateVelocity():

if (age > HorizonMilliseconds || delta > AssumePointerMoveStoppedMilliseconds) {
    break
}

At least on the slower Android 7.1.1 device (with a debug build) the delta is larger then 40, causing the calculateVelocity returning 0 afterwards because the sampleCount was only 1 (less then the minSampleSize of 3). When the Velocity is zero, eventually onPreFling will be called with that velocity.

VelocityTracker.samples contain:

1 = {DataPointAtTime@8181} DataPointAtTime(time=22150457, dataPoint=552.1706)
2 = {DataPointAtTime@8182} DataPointAtTime(time=22150469, dataPoint=550.1734)
3 = {DataPointAtTime@8183} DataPointAtTime(time=22150482, dataPoint=548.17615)
4 = {DataPointAtTime@8184} DataPointAtTime(time=22150483, dataPoint=548.09283)
5 = {DataPointAtTime@8185} DataPointAtTime(time=22150492, dataPoint=545.1803)
6 = {DataPointAtTime@8186} DataPointAtTime(time=22150503, dataPoint=543.1831)
7 = {DataPointAtTime@8187} DataPointAtTime(time=22150511, dataPoint=543.1831)
8 = {DataPointAtTime@8188} DataPointAtTime(time=22150515, dataPoint=543.1831)
9 = {DataPointAtTime@8189} DataPointAtTime(time=22150528, dataPoint=548.17615)
10 = {DataPointAtTime@8190} DataPointAtTime(time=22150549, dataPoint=558.73596)
11 = {DataPointAtTime@8168} DataPointAtTime(time=22150562, dataPoint=565.1526)
12 = {DataPointAtTime@8167} DataPointAtTime(time=22150606, dataPoint=565.1526)

The index of the loop is 11 at the time of executing the above break statement. What I find strange is that there are some duplicate data points with a different time

Any ideas on how to fix this and why AssumePointerMoveStoppedMilliseconds is 40ms would be appreciated.

Comments

le...@google.com <le...@google.com> Jun 23, 2023 01:25PM

Reassigned to le...@google.com.

wb...@gmail.com <wb...@gmail.com> #2Jul 17, 2023 01:47PM

Any idea on how I can further debug this issue? Thanks

le...@google.com <le...@google.com> #3Dec 28, 2023 04:09PM

Hi, sorry for the late response, not updates yet. There has been some updates to VelocityTrackerAddPointsFix you might want to try, but it looks like the slow device may be sending data too slowly to the tracker, AssumePointerMoveStoppedMilliseconds is 40ms because that's how the platform tracker works and the compose tracker uses a similar implementation. Let us know if the issue was fixed with the latest changes in VelocityTrackerAddPointsFix.

Thanks!

le...@google.com <le...@google.com> #4May 9, 2024 03:47PM

The fix from VelocityTrackerAddPointsFix will become available in the next stable release (1.7) it should fix this issue.

le...@google.com <le...@google.com> May 9, 2024 06:52PM

Status: Won't Fix (Obsolete)

Issue 288499763