From f4a86dd4e4be54c6552fc76990dd7d50d463fe06 Mon Sep 17 00:00:00 2001
From: Jordan Demeulenaere <jdemeulenaere@google.com>
Date: Tue, 11 Mar 2025 15:10:26 +0100
Subject: Add NestedDraggable.Controller.autoStopNestedDrags

This CL adds a new autoStopNestedDrags flag to
NestedDraggable.Controller to automatically stop a nested drag as soon
as it does not consume some amount of scroll. This will be used by the
media player to implement the "swipe to gear icon" behavior.

Bug: 397989775
Test: atest NestedDraggableTest
Flag: EXEMPT new unused API
Change-Id: If4441298d18a8c7fa9e4a84bdfb3e86a5dc426a1
---
 .../com/android/compose/gesture/NestedDraggable.kt | 19 ++++++++++--
 .../android/compose/gesture/NestedDraggableTest.kt | 36 ++++++++++++++++++++++
 2 files changed, 53 insertions(+), 2 deletions(-)

diff --git a/packages/SystemUI/compose/core/src/com/android/compose/gesture/NestedDraggable.kt b/packages/SystemUI/compose/core/src/com/android/compose/gesture/NestedDraggable.kt
index 80cbbea7659f..2ea9c487c27c 100644
--- a/packages/SystemUI/compose/core/src/com/android/compose/gesture/NestedDraggable.kt
+++ b/packages/SystemUI/compose/core/src/com/android/compose/gesture/NestedDraggable.kt
@@ -111,6 +111,14 @@ interface NestedDraggable {
     fun shouldConsumeNestedPreScroll(sign: Float): Boolean = false
 
     interface Controller {
+        /**
+         * Whether drags that were started from nested scrolls should be automatically
+         * [stopped][onDragStopped] as soon as they don't consume the entire `delta` passed to
+         * [onDrag].
+         */
+        val autoStopNestedDrags: Boolean
+            get() = false
+
         /**
          * Drag by [delta] pixels.
          *
@@ -609,8 +617,15 @@ private class NestedDraggableNode(
     }
 
     private fun scrollWithOverscroll(controller: NestedScrollController, offset: Offset): Offset {
-        return scrollWithOverscroll(offset) {
-            controller.controller.onDrag(it.toFloat()).toOffset()
+        return scrollWithOverscroll(offset) { delta ->
+            val available = delta.toFloat()
+            val consumed = controller.controller.onDrag(available)
+            if (controller.controller.autoStopNestedDrags && consumed != available) {
+                controller.ensureOnDragStoppedIsCalled()
+                this.nestedScrollController = null
+            }
+
+            consumed.toOffset()
         }
     }
 
diff --git a/packages/SystemUI/compose/core/tests/src/com/android/compose/gesture/NestedDraggableTest.kt b/packages/SystemUI/compose/core/tests/src/com/android/compose/gesture/NestedDraggableTest.kt
index a03d769c9c36..b247993de4e4 100644
--- a/packages/SystemUI/compose/core/tests/src/com/android/compose/gesture/NestedDraggableTest.kt
+++ b/packages/SystemUI/compose/core/tests/src/com/android/compose/gesture/NestedDraggableTest.kt
@@ -1000,6 +1000,39 @@ class NestedDraggableTest(override val orientation: Orientation) : OrientationAw
         assertThat(draggable.onDragStartedCalled).isTrue()
     }
 
+    @Test
+    fun autoStopNestedDrags() {
+        var consumeScrolls by mutableStateOf(true)
+        val draggable =
+            TestDraggable(autoStopNestedDrags = true, onDrag = { if (consumeScrolls) it else 0f })
+
+        val touchSlop =
+            rule.setContentWithTouchSlop {
+                Box(
+                    Modifier.fillMaxSize()
+                        .nestedDraggable(draggable, orientation)
+                        .scrollable(rememberScrollableState { 0f }, orientation)
+                )
+            }
+
+        rule.onRoot().performTouchInput {
+            down(center)
+            moveBy((touchSlop + 1f).toOffset())
+        }
+
+        assertThat(draggable.onDragStartedCalled).isTrue()
+        assertThat(draggable.onDragStoppedCalled).isFalse()
+
+        rule.onRoot().performTouchInput { moveBy(50f.toOffset()) }
+
+        assertThat(draggable.onDragStoppedCalled).isFalse()
+
+        consumeScrolls = false
+        rule.onRoot().performTouchInput { moveBy(1f.toOffset()) }
+
+        assertThat(draggable.onDragStoppedCalled).isTrue()
+    }
+
     private fun ComposeContentTestRule.setContentWithTouchSlop(
         content: @Composable () -> Unit
     ): Float {
@@ -1027,6 +1060,7 @@ class NestedDraggableTest(override val orientation: Orientation) : OrientationAw
             },
         private val shouldConsumeNestedPostScroll: (Float) -> Boolean = { true },
         private val shouldConsumeNestedPreScroll: (Float) -> Boolean = { false },
+        private val autoStopNestedDrags: Boolean = false,
     ) : NestedDraggable {
         var shouldStartDrag = true
         var onDragStartedCalled = false
@@ -1056,6 +1090,8 @@ class NestedDraggableTest(override val orientation: Orientation) : OrientationAw
 
             onDragStarted.invoke(position, sign)
             return object : NestedDraggable.Controller {
+                override val autoStopNestedDrags: Boolean = this@TestDraggable.autoStopNestedDrags
+
                 override fun onDrag(delta: Float): Float {
                     onDragCalled = true
                     onDragDelta += delta
-- 
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