Add support for swipes started from an edge

This CL adds support for swipes started from a specific edge. The
definition of edge is abstracted away into an EdgeDetector class, which
defaults to a fixed edge size of 40dp.

Bug: 291055080
Test: SwipeToSceneTest
Test: FixedSizeEdgeDetectorTest
Change-Id: I608ccefc26804c588e7568057e58606683cca8d7

7 files changed, 263 insertions, 13 deletions

diff --git a/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/EdgeDetector.kt b/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/EdgeDetector.kt
new file mode 100644
index 000000000000..82d4239d7eb5
--- /dev/null
+++ b/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/EdgeDetector.kt
@@ -0,0 +1,75 @@
+/*
+ * Copyright (C) 2023 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.compose.animation.scene
+
+import androidx.compose.foundation.gestures.Orientation
+import androidx.compose.ui.unit.Density
+import androidx.compose.ui.unit.Dp
+import androidx.compose.ui.unit.IntOffset
+import androidx.compose.ui.unit.IntSize
+import androidx.compose.ui.unit.dp
+
+interface EdgeDetector {
+    /**
+     * Return the [Edge] associated to [position] inside a layout of size [layoutSize], given
+     * [density] and [orientation].
+     */
+    fun edge(
+        layoutSize: IntSize,
+        position: IntOffset,
+        density: Density,
+        orientation: Orientation,
+    ): Edge?
+}
+
+val DefaultEdgeDetector = FixedSizeEdgeDetector(40.dp)
+
+/** An [EdgeDetector] that detects edges assuming a fixed edge size of [size]. */
+class FixedSizeEdgeDetector(val size: Dp) : EdgeDetector {
+    override fun edge(
+        layoutSize: IntSize,
+        position: IntOffset,
+        density: Density,
+        orientation: Orientation,
+    ): Edge? {
+        val axisSize: Int
+        val axisPosition: Int
+        val topOrLeft: Edge
+        val bottomOrRight: Edge
+        when (orientation) {
+            Orientation.Horizontal -> {
+                axisSize = layoutSize.width
+                axisPosition = position.x
+                topOrLeft = Edge.Left
+                bottomOrRight = Edge.Right
+            }
+            Orientation.Vertical -> {
+                axisSize = layoutSize.height
+                axisPosition = position.y
+                topOrLeft = Edge.Top
+                bottomOrRight = Edge.Bottom
+            }
+        }
+
+        val sizePx = with(density) { size.toPx() }
+        return when {
+            axisPosition <= sizePx -> topOrLeft
+            axisPosition >= axisSize - sizePx -> bottomOrRight
+            else -> null
+        }
+    }
+}
diff --git a/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SceneTransitionLayout.kt b/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SceneTransitionLayout.kt
index 4a1d73dbfcb1..1f38e70799c3 100644
--- a/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SceneTransitionLayout.kt
+++ b/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SceneTransitionLayout.kt
@@ -38,6 +38,7 @@ import androidx.compose.ui.platform.LocalDensity
  *   instance by triggering back navigation or by swiping to a new scene.
  * @param transitions the definition of the transitions used to animate a change of scene.
  * @param state the observable state of this layout.
+ * @param edgeDetector the edge detector used to detect which edge a swipe is started from, if any.
  * @param scenes the configuration of the different scenes of this layout.
  */
 @Composable
@@ -47,6 +48,7 @@ fun SceneTransitionLayout(
     transitions: SceneTransitions,
     modifier: Modifier = Modifier,
     state: SceneTransitionLayoutState = remember { SceneTransitionLayoutState(currentScene) },
+    edgeDetector: EdgeDetector = DefaultEdgeDetector,
     scenes: SceneTransitionLayoutScope.() -> Unit,
 ) {
     val density = LocalDensity.current
@@ -57,15 +59,17 @@ fun SceneTransitionLayout(
             transitions,
             state,
             density,
+            edgeDetector,
         )
     }
 
     layoutImpl.onChangeScene = onChangeScene
     layoutImpl.transitions = transitions
     layoutImpl.density = density
+    layoutImpl.edgeDetector = edgeDetector
+
     layoutImpl.setScenes(scenes)
     layoutImpl.setCurrentScene(currentScene)
-
     layoutImpl.Content(modifier)
 }
 
diff --git a/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SceneTransitionLayoutImpl.kt b/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SceneTransitionLayoutImpl.kt
index a40b29991877..a803a4770517 100644
--- a/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SceneTransitionLayoutImpl.kt
+++ b/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SceneTransitionLayoutImpl.kt
@@ -47,6 +47,7 @@ class SceneTransitionLayoutImpl(
     transitions: SceneTransitions,
     internal val state: SceneTransitionLayoutState,
     density: Density,
+    edgeDetector: EdgeDetector,
 ) {
     internal val scenes = SnapshotStateMap<SceneKey, Scene>()
     internal val elements = SnapshotStateMap<ElementKey, Element>()
@@ -57,6 +58,7 @@ class SceneTransitionLayoutImpl(
     internal var onChangeScene by mutableStateOf(onChangeScene)
     internal var transitions by mutableStateOf(transitions)
     internal var density: Density by mutableStateOf(density)
+    internal var edgeDetector by mutableStateOf(edgeDetector)
 
     /**
      * The size of this layout. Note that this could be [IntSize.Zero] if this layour does not have
diff --git a/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SwipeToScene.kt b/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SwipeToScene.kt
index 25b5db5c7506..ee1f13347840 100644
--- a/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SwipeToScene.kt
+++ b/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SwipeToScene.kt
@@ -35,6 +35,7 @@ import androidx.compose.ui.geometry.Offset
 import androidx.compose.ui.input.nestedscroll.nestedScroll
 import androidx.compose.ui.unit.Velocity
 import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.round
 import com.android.compose.nestedscroll.PriorityNestedScrollConnection
 import kotlin.math.absoluteValue
 import kotlinx.coroutines.CoroutineScope
@@ -157,7 +158,7 @@ class SceneGestureHandler(
 
     internal var gestureWithPriority: Any? = null
 
-    internal fun onDragStarted(pointersDown: Int) {
+    internal fun onDragStarted(pointersDown: Int, startedPosition: Offset?) {
         if (isDrivingTransition) {
             // This [transition] was already driving the animation: simply take over it.
             // Stop animating and start from where the current offset.
@@ -197,6 +198,16 @@ class SceneGestureHandler(
                 Orientation.Vertical -> layoutImpl.size.height
             }.toFloat()
 
+        val fromEdge =
+            startedPosition?.let { position ->
+                layoutImpl.edgeDetector.edge(
+                    layoutImpl.size,
+                    position.round(),
+                    layoutImpl.density,
+                    orientation,
+                )
+            }
+
         swipeTransition.actionUpOrLeft =
             Swipe(
                 direction =
@@ -205,6 +216,7 @@ class SceneGestureHandler(
                         Orientation.Vertical -> SwipeDirection.Up
                     },
                 pointerCount = pointersDown,
+                fromEdge = fromEdge,
             )
 
         swipeTransition.actionDownOrRight =
@@ -215,8 +227,19 @@ class SceneGestureHandler(
                         Orientation.Vertical -> SwipeDirection.Down
                     },
                 pointerCount = pointersDown,
+                fromEdge = fromEdge,
             )
 
+        if (fromEdge == null) {
+            swipeTransition.actionUpOrLeftNoEdge = null
+            swipeTransition.actionDownOrRightNoEdge = null
+        } else {
+            swipeTransition.actionUpOrLeftNoEdge =
+                (swipeTransition.actionUpOrLeft as Swipe).copy(fromEdge = null)
+            swipeTransition.actionDownOrRightNoEdge =
+                (swipeTransition.actionDownOrRight as Swipe).copy(fromEdge = null)
+        }
+
         if (swipeTransition.absoluteDistance > 0f) {
             transitionState = swipeTransition
         }
@@ -264,15 +287,11 @@ class SceneGestureHandler(
         // to the next screen or go back to the previous one.
         val offset = swipeTransition.dragOffset
         val absoluteDistance = swipeTransition.absoluteDistance
-        if (
-            offset <= -absoluteDistance &&
-                fromScene.userActions[swipeTransition.actionUpOrLeft] == toScene.key
-        ) {
+        if (offset <= -absoluteDistance && swipeTransition.upOrLeft(fromScene) == toScene.key) {
             swipeTransition.dragOffset += absoluteDistance
             swipeTransition._fromScene = toScene
         } else if (
-            offset >= absoluteDistance &&
-                fromScene.userActions[swipeTransition.actionDownOrRight] == toScene.key
+            offset >= absoluteDistance && swipeTransition.downOrRight(fromScene) == toScene.key
         ) {
             swipeTransition.dragOffset -= absoluteDistance
             swipeTransition._fromScene = toScene
@@ -294,8 +313,8 @@ class SceneGestureHandler(
                 Orientation.Vertical -> layoutImpl.size.height
             }.toFloat()
 
-        val upOrLeft = userActions[swipeTransition.actionUpOrLeft]
-        val downOrRight = userActions[swipeTransition.actionDownOrRight]
+        val upOrLeft = swipeTransition.upOrLeft(this)
+        val downOrRight = swipeTransition.downOrRight(this)
 
         // Compute the target scene depending on the current offset.
         return when {
@@ -542,6 +561,18 @@ class SceneGestureHandler(
         /** The [UserAction]s associated to this swipe. */
         var actionUpOrLeft: UserAction = Back
         var actionDownOrRight: UserAction = Back
+        var actionUpOrLeftNoEdge: UserAction? = null
+        var actionDownOrRightNoEdge: UserAction? = null
+
+        fun upOrLeft(scene: Scene): SceneKey? {
+            return scene.userActions[actionUpOrLeft]
+                ?: actionUpOrLeftNoEdge?.let { scene.userActions[it] }
+        }
+
+        fun downOrRight(scene: Scene): SceneKey? {
+            return scene.userActions[actionDownOrRight]
+                ?: actionDownOrRightNoEdge?.let { scene.userActions[it] }
+        }
     }
 
     companion object {
@@ -554,7 +585,7 @@ private class SceneDraggableHandler(
 ) : DraggableHandler {
     override fun onDragStarted(startedPosition: Offset, pointersDown: Int) {
         gestureHandler.gestureWithPriority = this
-        gestureHandler.onDragStarted(pointersDown)
+        gestureHandler.onDragStarted(pointersDown, startedPosition)
     }
 
     override fun onDelta(pixels: Float) {
@@ -671,7 +702,7 @@ class SceneNestedScrollHandler(
             onStart = {
                 gestureHandler.gestureWithPriority = this
                 priorityScene = nextScene
-                gestureHandler.onDragStarted(pointersDown = 1)
+                gestureHandler.onDragStarted(pointersDown = 1, startedPosition = null)
             },
             onScroll = { offsetAvailable ->
                 if (gestureHandler.gestureWithPriority != this) {
diff --git a/packages/SystemUI/compose/scene/tests/src/com/android/compose/animation/scene/FixedSizeEdgeDetectorTest.kt b/packages/SystemUI/compose/scene/tests/src/com/android/compose/animation/scene/FixedSizeEdgeDetectorTest.kt
new file mode 100644
index 000000000000..a68282ae78f4
--- /dev/null
+++ b/packages/SystemUI/compose/scene/tests/src/com/android/compose/animation/scene/FixedSizeEdgeDetectorTest.kt
@@ -0,0 +1,70 @@
+/*
+ * Copyright (C) 2023 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.compose.animation.scene
+
+import androidx.compose.foundation.gestures.Orientation
+import androidx.compose.ui.unit.Density
+import androidx.compose.ui.unit.IntOffset
+import androidx.compose.ui.unit.IntSize
+import androidx.compose.ui.unit.dp
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import com.google.common.truth.Truth.assertThat
+import org.junit.Test
+import org.junit.runner.RunWith
+
+@RunWith(AndroidJUnit4::class)
+class FixedSizeEdgeDetectorTest {
+    private val detector = FixedSizeEdgeDetector(30.dp)
+    private val layoutSize = IntSize(100, 100)
+    private val density = Density(1f)
+
+    @Test
+    fun horizontalEdges() {
+        fun horizontalEdge(position: Int): Edge? =
+            detector.edge(
+                layoutSize,
+                position = IntOffset(position, 0),
+                density,
+                Orientation.Horizontal,
+            )
+
+        assertThat(horizontalEdge(0)).isEqualTo(Edge.Left)
+        assertThat(horizontalEdge(30)).isEqualTo(Edge.Left)
+        assertThat(horizontalEdge(31)).isEqualTo(null)
+        assertThat(horizontalEdge(69)).isEqualTo(null)
+        assertThat(horizontalEdge(70)).isEqualTo(Edge.Right)
+        assertThat(horizontalEdge(100)).isEqualTo(Edge.Right)
+    }
+
+    @Test
+    fun verticalEdges() {
+        fun verticalEdge(position: Int): Edge? =
+            detector.edge(
+                layoutSize,
+                position = IntOffset(0, position),
+                density,
+                Orientation.Vertical,
+            )
+
+        assertThat(verticalEdge(0)).isEqualTo(Edge.Top)
+        assertThat(verticalEdge(30)).isEqualTo(Edge.Top)
+        assertThat(verticalEdge(31)).isEqualTo(null)
+        assertThat(verticalEdge(69)).isEqualTo(null)
+        assertThat(verticalEdge(70)).isEqualTo(Edge.Bottom)
+        assertThat(verticalEdge(100)).isEqualTo(Edge.Bottom)
+    }
+}
diff --git a/packages/SystemUI/compose/scene/tests/src/com/android/compose/animation/scene/SceneGestureHandlerTest.kt b/packages/SystemUI/compose/scene/tests/src/com/android/compose/animation/scene/SceneGestureHandlerTest.kt
index 4b3fbdf77274..1eb3392f1374 100644
--- a/packages/SystemUI/compose/scene/tests/src/com/android/compose/animation/scene/SceneGestureHandlerTest.kt
+++ b/packages/SystemUI/compose/scene/tests/src/com/android/compose/animation/scene/SceneGestureHandlerTest.kt
@@ -55,7 +55,8 @@ class SceneGestureHandlerTest {
                             builder = scenesBuilder,
                             transitions = EmptyTestTransitions,
                             state = layoutState,
-                            density = Density(1f)
+                            density = Density(1f),
+                            edgeDetector = DefaultEdgeDetector,
                         )
                         .also { it.size = IntSize(SCREEN_SIZE.toInt(), SCREEN_SIZE.toInt()) },
                 orientation = Orientation.Vertical,
diff --git a/packages/SystemUI/compose/scene/tests/src/com/android/compose/animation/scene/SwipeToSceneTest.kt b/packages/SystemUI/compose/scene/tests/src/com/android/compose/animation/scene/SwipeToSceneTest.kt
index 6ad2108c05a5..4a6066f5c664 100644
--- a/packages/SystemUI/compose/scene/tests/src/com/android/compose/animation/scene/SwipeToSceneTest.kt
+++ b/packages/SystemUI/compose/scene/tests/src/com/android/compose/animation/scene/SwipeToSceneTest.kt
@@ -48,6 +48,14 @@ class SwipeToSceneTest {
         /** The middle of the layout, in pixels. */
         private val Density.middle: Offset
             get() = Offset((LayoutWidth / 2).toPx(), (LayoutHeight / 2).toPx())
+
+        /** The middle-top of the layout, in pixels. */
+        private val Density.middleTop: Offset
+            get() = Offset((LayoutWidth / 2).toPx(), 0f)
+
+        /** The middle-left of the layout, in pixels. */
+        private val Density.middleLeft: Offset
+            get() = Offset(0f, (LayoutHeight / 2).toPx())
     }
 
     private var currentScene by mutableStateOf(TestScenes.SceneA)
@@ -87,6 +95,8 @@ class SwipeToSceneTest {
                     mapOf(
                         Swipe.Down to TestScenes.SceneA,
                         Swipe(SwipeDirection.Down, pointerCount = 2) to TestScenes.SceneB,
+                        Swipe(SwipeDirection.Right, fromEdge = Edge.Left) to TestScenes.SceneB,
+                        Swipe(SwipeDirection.Down, fromEdge = Edge.Top) to TestScenes.SceneB,
                     ),
             ) {
                 Box(Modifier.fillMaxSize())
@@ -285,4 +295,61 @@ class SwipeToSceneTest {
         assertThat(layoutState.transitionState).isInstanceOf(TransitionState.Idle::class.java)
         assertThat(layoutState.transitionState.currentScene).isEqualTo(TestScenes.SceneC)
     }
+
+    @Test
+    fun defaultEdgeSwipe() {
+        // Start at scene C.
+        currentScene = TestScenes.SceneC
+
+        // The draggable touch slop, i.e. the min px distance a touch pointer must move before it is
+        // detected as a drag event.
+        var touchSlop = 0f
+        rule.setContent {
+            touchSlop = LocalViewConfiguration.current.touchSlop
+            TestContent()
+        }
+
+        assertThat(layoutState.transitionState).isInstanceOf(TransitionState.Idle::class.java)
+        assertThat(layoutState.transitionState.currentScene).isEqualTo(TestScenes.SceneC)
+
+        // Swipe down from the top edge.
+        rule.onRoot().performTouchInput {
+            down(middleTop)
+            moveBy(Offset(0f, touchSlop + 10.dp.toPx()), delayMillis = 1_000)
+        }
+
+        // We are transitioning to B (and not A) because we started from the top edge.
+        var transition = layoutState.transitionState
+        assertThat(transition).isInstanceOf(TransitionState.Transition::class.java)
+        assertThat((transition as TransitionState.Transition).fromScene)
+            .isEqualTo(TestScenes.SceneC)
+        assertThat(transition.toScene).isEqualTo(TestScenes.SceneB)
+
+        // Release the fingers and wait for the animation to end. We are back to C because we only
+        // swiped 10dp.
+        rule.onRoot().performTouchInput { up() }
+        rule.waitForIdle()
+        assertThat(layoutState.transitionState).isInstanceOf(TransitionState.Idle::class.java)
+        assertThat(layoutState.transitionState.currentScene).isEqualTo(TestScenes.SceneC)
+
+        // Swipe right from the left edge.
+        rule.onRoot().performTouchInput {
+            down(middleLeft)
+            moveBy(Offset(touchSlop + 10.dp.toPx(), 0f), delayMillis = 1_000)
+        }
+
+        // We are transitioning to B (and not A) because we started from the left edge.
+        transition = layoutState.transitionState
+        assertThat(transition).isInstanceOf(TransitionState.Transition::class.java)
+        assertThat((transition as TransitionState.Transition).fromScene)
+            .isEqualTo(TestScenes.SceneC)
+        assertThat(transition.toScene).isEqualTo(TestScenes.SceneB)
+
+        // Release the fingers and wait for the animation to end. We are back to C because we only
+        // swiped 10dp.
+        rule.onRoot().performTouchInput { up() }
+        rule.waitForIdle()
+        assertThat(layoutState.transitionState).isInstanceOf(TransitionState.Idle::class.java)
+        assertThat(layoutState.transitionState.currentScene).isEqualTo(TestScenes.SceneC)
+    }
 }