Fling animation does not trigger if gesture is fast [197553056]

Fixed

Bug

Status Update

No update yet.

Description

si...@gmail.com

created issue #1

Aug 24, 2021 06:20AM

Jetpack Compose release version: 1.0.0

Steps to Reproduce:

Create any scrollable - verticalScroll(), LazyColumn etc
Perform very fast fling gesture
Fling velocity in FlingBehavior is zero

This issue is more noticeable on slower devices. Also reproduces with 1.1.0-alpha02

Column(Modifier.verticalScroll(rememberScrollState())) {
    for (it in 1..100) {
        Surface(Modifier.fillMaxWidth()) {
            ListItem {
                Text("Item #$it")
            }
        }
    }
}

2021-08-24 09.17.16.mp4

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Comments

je...@google.com <je...@google.com> #2Aug 25, 2021 12:04PM

Assigned to mo...@google.com.

Hi, thanks for reporting this.

For calculating the velocity of a fling, Compose's VelocityTracker needs at least 3 data points (input events). On Android, if input events are generated faster than they can be handled, they will be batched together in a single MotionEvent, and they are accessible through the event's history. Currently, Compose doesn't process such historical data yet, which means that a set of X batched motion events is handled as a single motion event. That explains why on slower devices you're more likely to see this error (as it's more likely that events are batched). Android's native VelocityTracker does handle historical data, which is why it was less likely to see this in Views.

We'll look into this

Message last modified on Aug 25, 2021 12:05PM

ae...@google.com <ae...@google.com> Sep 15, 2021 03:12AM

Accepted by ae...@google.com.

ap...@google.com <ap...@google.com> #3Sep 22, 2021 01:28AM

Marked as fixed.

Project: platform/frameworks/support
Branch: androidx-main

commit 9446c48c42cd9583bf86249eda1aa2e1bb3c59d5
Author: Alexandre Elias <aelias@google.com>
Date: Thu Sep 16 20:15:37 2021

Velocity tracking for historical changes

This forwards the additional "historical" pointer information in
MotionEvent to the fling velocity tracker, allowing more accurate fling
detection.

It also forwards ordinary pointer information for the
first DOWN event and first (slop) MOVE event, matching the framework
velocity tracker.

Test: MoveWithHistoryTest.flingScrollableWithHistorical
Fixes: 197553056
Fixes: 199914454
Bug: 199921305
Relnote: Added experimental historical pointers to PointerEventChange.

Change-Id: Ic1fd82fd3f2335a9289cc1fc96c35e89ec9b90ee

M compose/ui/ui-test/src/androidMain/kotlin/androidx/compose/ui/test/AndroidInputDispatcher.android.kt
M compose/ui/ui/src/androidMain/kotlin/androidx/compose/ui/input/pointer/MotionEventAdapter.android.kt
M compose/ui/ui-test/api/public_plus_experimental_current.txt
M compose/ui/ui-test/src/commonMain/kotlin/androidx/compose/ui/test/MultiModalInjectionScope.kt
M compose/foundation/foundation/src/commonMain/kotlin/androidx/compose/foundation/gestures/Draggable.kt
M compose/ui/ui-test/src/commonMain/kotlin/androidx/compose/ui/test/TouchInjectionScope.kt
A compose/ui/ui-test/src/androidAndroidTest/kotlin/androidx/compose/ui/test/injectionscope/touch/MoveWithHistoryTest.kt
M compose/ui/ui/api/current.txt
M compose/ui/ui/src/androidAndroidTest/kotlin/androidx/compose/ui/input/pointer/PointerInputEventProcessorTest.kt
M compose/ui/ui/src/commonMain/kotlin/androidx/compose/ui/input/pointer/util/VelocityTracker.kt
M compose/ui/ui-test/src/commonMain/kotlin/androidx/compose/ui/test/InputDispatcher.kt
M compose/ui/ui/src/commonMain/kotlin/androidx/compose/ui/input/pointer/PointerInputEventProcessor.kt
M compose/ui/ui/src/commonMain/kotlin/androidx/compose/ui/input/pointer/PointerEvent.kt
M compose/foundation/foundation/src/androidAndroidTest/kotlin/androidx/compose/foundation/ScrollableTest.kt
M compose/ui/ui/src/commonMain/kotlin/androidx/compose/ui/input/pointer/HitPathTracker.kt
M compose/ui/ui/src/commonMain/kotlin/androidx/compose/ui/input/pointer/InternalPointerInput.kt
M compose/ui/ui/api/restricted_current.txt
M compose/foundation/foundation/src/androidAndroidTest/kotlin/androidx/compose/foundation/gesture/OverScrollTest.kt
M compose/ui/ui-test/src/desktopMain/kotlin/androidx/compose/ui/test/DesktopInputDispatcher.desktop.kt
M compose/ui/ui/api/public_plus_experimental_current.txt

https://android-review.googlesource.com/1826965

al...@gmail.com <al...@gmail.com> #4Mar 8, 2022 09:44PM

Velocity Tracker in compose has an issue.
When I scroll on a composable and concurrently change offset of that composable by scroll delta ,every point that add to Velocity Tracker approximately has same offset , so velocity calculate incorrect.
The issue can be solved if drag amount be used instead of offset of pointer.
When layout is fixed it work well but when layout move by changing offset or translation this issue will be happen.

Message last modified on Mar 9, 2022 07:50AM

al...@gmail.com <al...@gmail.com> #5Mar 9, 2022 02:05PM

I also encountered this bug. It may be related to this old issue: https://issuetracker.google.com/issues/179417109

Unfortunately it doesn't seem to get much attention and is a blocker for a simple bottom sheet with a lazy list inside.

Issue 197553056