Make it possible to change the swipe animation spec

This CL adds a way to change the default spring spec used when animating
a transition that started with a user gesture.

Bug: 322316041
Test: TransitionDslTest
Flag: N/A
Change-Id: Ia1310340580d9910d45e93067aee0658559953ba

5 files changed, 111 insertions, 19 deletions

diff --git a/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SceneGestureHandler.kt b/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SceneGestureHandler.kt
index 8305428aa9c8..58c3be244725 100644
--- a/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SceneGestureHandler.kt
+++ b/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SceneGestureHandler.kt
@@ -20,8 +20,7 @@ package com.android.compose.animation.scene
 
 import android.util.Log
 import androidx.compose.animation.core.Animatable
-import androidx.compose.animation.core.Spring
-import androidx.compose.animation.core.spring
+import androidx.compose.animation.core.SpringSpec
 import androidx.compose.foundation.gestures.Orientation
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableFloatStateOf
@@ -54,7 +53,20 @@ internal class SceneGestureHandler(
         }
 
     private fun updateTransition(newTransition: SwipeTransition, force: Boolean = false) {
-        if (isDrivingTransition || force) layoutState.startTransition(newTransition)
+        if (isDrivingTransition || force) {
+            layoutState.startTransition(newTransition)
+
+            // Initialize SwipeTransition.swipeSpec. Note that this must be called right after
+            // layoutState.startTransition() is called, because it computes the
+            // layoutState.transformationSpec().
+            newTransition.swipeSpec =
+                layoutState.transformationSpec.swipeSpec ?: layoutState.transitions.defaultSwipeSpec
+        } else {
+            // We were not driving the transition and we don't force the update, so the spec won't
+            // be used and it doesn't matter which one we set here.
+            newTransition.swipeSpec = SceneTransitions.DefaultSwipeSpec
+        }
+
         swipeTransition = newTransition
     }
 
@@ -491,7 +503,7 @@ internal class SceneGestureHandler(
          * The signed distance between [fromScene] and [toScene]. It is negative if [fromScene] is
          * above or to the left of [toScene].
          */
-        val distance: Float
+        val distance: Float,
     ) : TransitionState.Transition(_fromScene.key, _toScene.key) {
         var _currentScene by mutableStateOf(_fromScene)
         override val currentScene: SceneKey
@@ -524,6 +536,9 @@ internal class SceneGestureHandler(
         /** Job to check that there is at most one offset animation in progress. */
         private var offsetAnimationJob: Job? = null
 
+        /** The spec to use when animating this transition to either [fromScene] or [toScene]. */
+        lateinit var swipeSpec: SpringSpec<Float>
+
         /** Ends any previous [offsetAnimationJob] and runs the new [job]. */
         private fun startOffsetAnimation(job: () -> Job) {
             cancelOffsetAnimation()
@@ -545,13 +560,6 @@ internal class SceneGestureHandler(
             }
         }
 
-        // TODO(b/290184746): Make this spring spec configurable.
-        private val animationSpec =
-            spring(
-                stiffness = Spring.StiffnessMediumLow,
-                visibilityThreshold = OffsetVisibilityThreshold
-            )
-
         fun animateOffset(
             // TODO(b/317063114) The CoroutineScope should be removed.
             coroutineScope: CoroutineScope,
@@ -575,7 +583,7 @@ internal class SceneGestureHandler(
 
             offsetAnimatable.animateTo(
                 targetValue = targetOffset,
-                animationSpec = animationSpec,
+                animationSpec = swipeSpec,
                 initialVelocity = initialVelocity,
             )
 
@@ -811,4 +819,6 @@ internal class SceneNestedScrollHandler(
  * The number of pixels below which there won't be a visible difference in the transition and from
  * which the animation can stop.
  */
-private const val OffsetVisibilityThreshold = 0.5f
+// TODO(b/290184746): Have a better default visibility threshold which takes the swipe distance into
+// account instead.
+internal const val OffsetVisibilityThreshold = 0.5f
diff --git a/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SceneTransitions.kt b/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SceneTransitions.kt
index 3a55567d69bb..ac423b70fd50 100644
--- a/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SceneTransitions.kt
+++ b/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SceneTransitions.kt
@@ -17,7 +17,10 @@
 package com.android.compose.animation.scene
 
 import androidx.compose.animation.core.AnimationSpec
+import androidx.compose.animation.core.Spring
+import androidx.compose.animation.core.SpringSpec
 import androidx.compose.animation.core.snap
+import androidx.compose.animation.core.spring
 import androidx.compose.ui.geometry.Offset
 import androidx.compose.ui.unit.IntSize
 import androidx.compose.ui.util.fastForEach
@@ -36,6 +39,7 @@ import com.android.compose.animation.scene.transformation.Translate
 /** The transitions configuration of a [SceneTransitionLayout]. */
 class SceneTransitions
 internal constructor(
+    internal val defaultSwipeSpec: SpringSpec<Float>,
     internal val transitionSpecs: List<TransitionSpecImpl>,
 ) {
     private val cache = mutableMapOf<SceneKey, MutableMap<SceneKey, TransitionSpecImpl>>()
@@ -91,7 +95,13 @@ internal constructor(
         TransitionSpecImpl(from, to, TransformationSpec.EmptyProvider)
 
     companion object {
-        val Empty = SceneTransitions(transitionSpecs = emptyList())
+        internal val DefaultSwipeSpec =
+            spring(
+                stiffness = Spring.StiffnessMediumLow,
+                visibilityThreshold = OffsetVisibilityThreshold,
+            )
+
+        val Empty = SceneTransitions(DefaultSwipeSpec, transitionSpecs = emptyList())
     }
 }
 
@@ -125,15 +135,30 @@ interface TransitionSpec {
 }
 
 interface TransformationSpec {
-    /** The [AnimationSpec] used to animate the associated transition progress. */
+    /**
+     * The [AnimationSpec] used to animate the associated transition progress from `0` to `1` when
+     * the transition is triggered (i.e. it is not gesture-based).
+     */
     val progressSpec: AnimationSpec<Float>
 
+    /**
+     * The [SpringSpec] used to animate the associated transition progress when the transition was
+     * started by a swipe and is now animating back to a scene because the user lifted their finger.
+     *
+     * If `null`, then the [SceneTransitions.defaultSwipeSpec] will be used.
+     */
+    val swipeSpec: SpringSpec<Float>?
+
     /** The list of [Transformation] applied to elements during this transition. */
     val transformations: List<Transformation>
 
     companion object {
         internal val Empty =
-            TransformationSpecImpl(progressSpec = snap(), transformations = emptyList())
+            TransformationSpecImpl(
+                progressSpec = snap(),
+                swipeSpec = null,
+                transformations = emptyList(),
+            )
         internal val EmptyProvider = { Empty }
     }
 }
@@ -151,6 +176,7 @@ internal class TransitionSpecImpl(
                 val reverse = transformationSpec.invoke()
                 TransformationSpecImpl(
                     progressSpec = reverse.progressSpec,
+                    swipeSpec = reverse.swipeSpec,
                     transformations = reverse.transformations.map { it.reversed() }
                 )
             }
@@ -166,6 +192,7 @@ internal class TransitionSpecImpl(
  */
 internal class TransformationSpecImpl(
     override val progressSpec: AnimationSpec<Float>,
+    override val swipeSpec: SpringSpec<Float>?,
     override val transformations: List<Transformation>,
 ) : TransformationSpec {
     private val cache = mutableMapOf<ElementKey, MutableMap<SceneKey, ElementTransformations>>()
diff --git a/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/TransitionDsl.kt b/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/TransitionDsl.kt
index a764a52723af..04e093721824 100644
--- a/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/TransitionDsl.kt
+++ b/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/TransitionDsl.kt
@@ -17,6 +17,7 @@
 package com.android.compose.animation.scene
 
 import androidx.compose.animation.core.AnimationSpec
+import androidx.compose.animation.core.SpringSpec
 import androidx.compose.ui.geometry.Offset
 import androidx.compose.ui.unit.Dp
 import androidx.compose.ui.unit.dp
@@ -31,6 +32,12 @@ fun transitions(builder: SceneTransitionsBuilder.() -> Unit): SceneTransitions {
 @TransitionDsl
 interface SceneTransitionsBuilder {
     /**
+     * The default [AnimationSpec] used when after the user lifts their finger after starting a
+     * swipe to transition, to animate back into one of the 2 scenes we are transitioning to.
+     */
+    var defaultSwipeSpec: SpringSpec<Float>
+
+    /**
      * Define the default animation to be played when transitioning [to] the specified scene, from
      * any scene. For the animation specification to apply only when transitioning between two
      * specific scenes, use [from] instead.
@@ -64,12 +71,20 @@ interface SceneTransitionsBuilder {
 @TransitionDsl
 interface TransitionBuilder : PropertyTransformationBuilder {
     /**
-     * The [AnimationSpec] used to animate the progress of this transition from `0` to `1` when
-     * performing programmatic (not input pointer tracking) animations.
+     * The [AnimationSpec] used to animate the associated transition progress from `0` to `1` when
+     * the transition is triggered (i.e. it is not gesture-based).
      */
     var spec: AnimationSpec<Float>
 
     /**
+     * The [SpringSpec] used to animate the associated transition progress when the transition was
+     * started by a swipe and is now animating back to a scene because the user lifted their finger.
+     *
+     * If `null`, then the [SceneTransitionsBuilder.defaultSwipeSpec] will be used.
+     */
+    var swipeSpec: SpringSpec<Float>?
+
+    /**
      * Define a progress-based range for the transformations inside [builder].
      *
      * For instance, the following will fade `Foo` during the first half of the transition then it
diff --git a/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/TransitionDslImpl.kt b/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/TransitionDslImpl.kt
index b96f9bebb08b..df186a15181e 100644
--- a/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/TransitionDslImpl.kt
+++ b/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/TransitionDslImpl.kt
@@ -19,6 +19,7 @@ package com.android.compose.animation.scene
 import androidx.compose.animation.core.AnimationSpec
 import androidx.compose.animation.core.DurationBasedAnimationSpec
 import androidx.compose.animation.core.Spring
+import androidx.compose.animation.core.SpringSpec
 import androidx.compose.animation.core.VectorConverter
 import androidx.compose.animation.core.spring
 import androidx.compose.ui.geometry.Offset
@@ -40,10 +41,12 @@ internal fun transitionsImpl(
     builder: SceneTransitionsBuilder.() -> Unit,
 ): SceneTransitions {
     val impl = SceneTransitionsBuilderImpl().apply(builder)
-    return SceneTransitions(impl.transitionSpecs)
+    return SceneTransitions(impl.defaultSwipeSpec, impl.transitionSpecs)
 }
 
 private class SceneTransitionsBuilderImpl : SceneTransitionsBuilder {
+    override var defaultSwipeSpec: SpringSpec<Float> = SceneTransitions.DefaultSwipeSpec
+
     val transitionSpecs = mutableListOf<TransitionSpecImpl>()
 
     override fun to(to: SceneKey, builder: TransitionBuilder.() -> Unit): TransitionSpec {
@@ -67,6 +70,7 @@ private class SceneTransitionsBuilderImpl : SceneTransitionsBuilder {
             val impl = TransitionBuilderImpl().apply(builder)
             return TransformationSpecImpl(
                 progressSpec = impl.spec,
+                swipeSpec = impl.swipeSpec,
                 transformations = impl.transformations,
             )
         }
@@ -80,6 +84,7 @@ private class SceneTransitionsBuilderImpl : SceneTransitionsBuilder {
 internal class TransitionBuilderImpl : TransitionBuilder {
     val transformations = mutableListOf<Transformation>()
     override var spec: AnimationSpec<Float> = spring(stiffness = Spring.StiffnessLow)
+    override var swipeSpec: SpringSpec<Float>? = null
 
     private var range: TransformationRange? = null
     private var reversed = false
diff --git a/packages/SystemUI/compose/scene/tests/src/com/android/compose/animation/scene/TransitionDslTest.kt b/packages/SystemUI/compose/scene/tests/src/com/android/compose/animation/scene/TransitionDslTest.kt
index ef729921f4cd..140bacaec738 100644
--- a/packages/SystemUI/compose/scene/tests/src/com/android/compose/animation/scene/TransitionDslTest.kt
+++ b/packages/SystemUI/compose/scene/tests/src/com/android/compose/animation/scene/TransitionDslTest.kt
@@ -18,6 +18,7 @@ package com.android.compose.animation.scene
 
 import androidx.compose.animation.core.SpringSpec
 import androidx.compose.animation.core.TweenSpec
+import androidx.compose.animation.core.spring
 import androidx.compose.animation.core.tween
 import androidx.test.ext.junit.runners.AndroidJUnit4
 import com.android.compose.animation.scene.transformation.Transformation
@@ -188,6 +189,40 @@ class TransitionDslTest {
             )
     }
 
+    @Test
+    fun springSpec() {
+        val defaultSpec = spring<Float>(stiffness = 1f)
+        val specFromAToC = spring<Float>(stiffness = 2f)
+        val transitions = transitions {
+            defaultSwipeSpec = defaultSpec
+
+            from(TestScenes.SceneA, to = TestScenes.SceneB) {
+                // Default swipe spec.
+            }
+            from(TestScenes.SceneA, to = TestScenes.SceneC) { swipeSpec = specFromAToC }
+        }
+
+        assertThat(transitions.defaultSwipeSpec).isSameInstanceAs(defaultSpec)
+
+        // A => B does not have a custom spec.
+        assertThat(
+                transitions
+                    .transitionSpec(from = TestScenes.SceneA, to = TestScenes.SceneB)
+                    .transformationSpec()
+                    .swipeSpec
+            )
+            .isNull()
+
+        // A => C has a custom swipe spec.
+        assertThat(
+                transitions
+                    .transitionSpec(from = TestScenes.SceneA, to = TestScenes.SceneC)
+                    .transformationSpec()
+                    .swipeSpec
+            )
+            .isSameInstanceAs(specFromAToC)
+    }
+
     companion object {
         private val TRANSFORMATION_RANGE =
             Correspondence.transforming<Transformation, TransformationRange?>(