animateOffset can partially consume the fling velocity

When a scene is configured to disallow overscrolling
(`overscrollDisabled()` is enabled), a fling gesture on that scene may
not use up all of the velocity. The unused velocity can then be passed
on to the ancestor of the component.

Test: atest DraggableHandlerTest
Bug: 336710600
Flag: com.android.systemui.scene_container
Change-Id: Ia1b0620fe37cfaf5b339d1e87c38ba5c22be95e8

2 files changed, 30 insertions, 4 deletions

diff --git a/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SwipeAnimation.kt b/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SwipeAnimation.kt
index 18d8328b2856..205267da151a 100644
--- a/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SwipeAnimation.kt
+++ b/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SwipeAnimation.kt
@@ -28,10 +28,8 @@ import androidx.compose.ui.unit.IntSize
 import com.android.compose.animation.scene.content.state.TransitionState
 import com.android.compose.animation.scene.content.state.TransitionState.HasOverscrollProperties.Companion.DistanceUnspecified
 import com.android.compose.nestedscroll.SuspendedValue
-import kotlinx.coroutines.CancellationException
 import kotlin.math.absoluteValue
 import kotlinx.coroutines.CompletableDeferred
-import kotlinx.coroutines.withTimeout
 
 internal fun createSwipeAnimation(
     layoutState: MutableSceneTransitionLayoutStateImpl,
@@ -425,6 +423,9 @@ internal class SwipeAnimation<T : ContentKey>(
                             // Immediately stop this transition if we are bouncing on a content that
                             // does not bounce.
                             if (!contentTransition.isWithinProgressRange(progress)) {
+                                // We are no longer able to consume the velocity, the rest can be
+                                // consumed by another component in the hierarchy.
+                                velocityConsumed.complete(initialVelocity - velocity)
                                 throw SnapException()
                             }
                         }
@@ -433,8 +434,10 @@ internal class SwipeAnimation<T : ContentKey>(
             } catch (_: SnapException) {
                 /* Ignore. */
             } finally {
-                // The animation consumed the whole available velocity
-                velocityConsumed.complete(initialVelocity)
+                if (!velocityConsumed.isCompleted) {
+                    // The animation consumed the whole available velocity
+                    velocityConsumed.complete(initialVelocity)
+                }
             }
         }
 
diff --git a/packages/SystemUI/compose/scene/tests/src/com/android/compose/animation/scene/DraggableHandlerTest.kt b/packages/SystemUI/compose/scene/tests/src/com/android/compose/animation/scene/DraggableHandlerTest.kt
index c0524b730ab8..2c41b35da998 100644
--- a/packages/SystemUI/compose/scene/tests/src/com/android/compose/animation/scene/DraggableHandlerTest.kt
+++ b/packages/SystemUI/compose/scene/tests/src/com/android/compose/animation/scene/DraggableHandlerTest.kt
@@ -1177,6 +1177,29 @@ class DraggableHandlerTest {
     }
 
     @Test
+    fun emptyOverscrollAbortsSettleAnimationAndExposeTheConsumedVelocity() = runGestureTest {
+        // Overscrolling on scene B does nothing.
+        layoutState.transitions = transitions { overscrollDisabled(SceneB, Orientation.Vertical) }
+
+        // Swipe up to scene B at progress = 200%.
+        val middle = Offset(SCREEN_SIZE / 2f, SCREEN_SIZE / 2f)
+        val dragController = onDragStarted(startedPosition = middle, overSlop = up(0.99f))
+        assertTransition(fromScene = SceneA, toScene = SceneB, progress = 0.99f)
+
+        // Release the finger.
+        dragController.onDragStoppedAnimateNow(
+            velocity = -velocityThreshold,
+            onAnimationStart = { assertTransition(fromScene = SceneA, toScene = SceneB) },
+            onAnimationEnd = { consumedVelocity ->
+                // Our progress value was 0.99f and it is coerced in `[0..1]` (overscrollDisabled).
+                // Some of the velocity will be used for animation, but not all of it.
+                assertThat(consumedVelocity).isLessThan(0f)
+                assertThat(consumedVelocity).isGreaterThan(-velocityThreshold)
+            },
+        )
+    }
+
+    @Test
     fun overscroll_releaseBetween0And100Percent_up() = runGestureTest {
         // Make scene B overscrollable.
         layoutState.transitions = transitions {