/*
* Copyright 2020 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 androidx.compose.foundation.gestures
import androidx.compose.animation.core.AnimationState
import androidx.compose.animation.core.DecayAnimationSpec
import androidx.compose.animation.core.animateDecay
import androidx.compose.animation.rememberSplineBasedDecay
import androidx.compose.foundation.MutatePriority
import androidx.compose.foundation.gestures.Orientation.Horizontal
import androidx.compose.foundation.interaction.MutableInteractionSource
import androidx.compose.runtime.Composable
import androidx.compose.runtime.State
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.rememberUpdatedState
import androidx.compose.ui.ExperimentalComposeUiApi
import androidx.compose.ui.Modifier
import androidx.compose.ui.composed
import androidx.compose.ui.geometry.Offset
import androidx.compose.ui.input.nestedscroll.NestedScrollConnection
import androidx.compose.ui.input.nestedscroll.NestedScrollDispatcher
import androidx.compose.ui.input.nestedscroll.NestedScrollSource
import androidx.compose.ui.input.nestedscroll.NestedScrollSource.Companion.Drag
import androidx.compose.ui.input.nestedscroll.NestedScrollSource.Companion.Fling
import androidx.compose.ui.input.nestedscroll.NestedScrollSource.Companion.Relocate
import androidx.compose.ui.input.nestedscroll.nestedScroll
import androidx.compose.ui.input.pointer.PointerType
import androidx.compose.ui.platform.debugInspectorInfo
import androidx.compose.ui.unit.Velocity
import kotlinx.coroutines.launch
import kotlin.math.abs
/**
* Configure touch scrolling and flinging for the UI element in a single [Orientation].
*
* Users should update their state themselves using default [ScrollableState] and its
* `consumeScrollDelta` callback or by implementing [ScrollableState] interface manually and reflect
* their own state in UI when using this component.
*
* If you don't need to have fling or nested scroll support, but want to make component simply
* draggable, consider using [draggable].
*
* @sample androidx.compose.foundation.samples.ScrollableSample
*
* @param state [ScrollableState] state of the scrollable. Defines how scroll events will be
* interpreted by the user land logic and contains useful information about on-going events.
* @param orientation orientation of the scrolling
* @param enabled whether or not scrolling in enabled
* @param reverseDirection reverse the direction of the scroll, so top to bottom scroll will
* behave like bottom to top and left to right will behave like right to left.
* @param flingBehavior logic describing fling behavior when drag has finished with velocity. If
* `null`, default from [ScrollableDefaults.flingBehavior] will be used.
* @param interactionSource [MutableInteractionSource] that will be used to emit
* drag events when this scrollable is being dragged.
*/
fun Modifier.scrollable(
state: ScrollableState,
orientation: Orientation,
enabled: Boolean = true,
reverseDirection: Boolean = false,
flingBehavior: FlingBehavior? = null,
interactionSource: MutableInteractionSource? = null
): Modifier = composed(
inspectorInfo = debugInspectorInfo {
name = "scrollable"
properties["orientation"] = orientation
properties["state"] = state
properties["enabled"] = enabled
properties["reverseDirection"] = reverseDirection
properties["flingBehavior"] = flingBehavior
properties["interactionSource"] = interactionSource
},
factory = {
fun Float.reverseIfNeeded(): Float = if (reverseDirection) this * -1 else this
touchScrollImplementation(
interactionSource,
orientation,
reverseDirection,
state,
flingBehavior,
enabled
).mouseScrollable(orientation) {
state.dispatchRawDelta(it.reverseIfNeeded())
}
}
)
/**
* Contains the default values used by [scrollable]
*/
object ScrollableDefaults {
/**
* Create and remember default [FlingBehavior] that will represent natural fling curve.
*/
@Composable
fun flingBehavior(): FlingBehavior {
val flingSpec = rememberSplineBasedDecay<Float>()
return remember(flingSpec) {
DefaultFlingBehavior(flingSpec)
}
}
}
// TODO(demin): think how we can move touchScrollable/mouseScrollable into commonMain,
// so Android can support mouse wheel scrolling, and desktop can support touch scrolling.
// For this we need first to implement different types of PointerInputEvent
// (to differentiate mouse and touch)
internal expect fun Modifier.mouseScrollable(
orientation: Orientation,
onScroll: (Float) -> Unit
): Modifier
@Suppress("ComposableModifierFactory")
@Composable
private fun Modifier.touchScrollImplementation(
interactionSource: MutableInteractionSource?,
orientation: Orientation,
reverseDirection: Boolean,
controller: ScrollableState,
flingBehavior: FlingBehavior?,
enabled: Boolean
): Modifier {
val fling = flingBehavior ?: ScrollableDefaults.flingBehavior()
val nestedScrollDispatcher = remember { mutableStateOf(NestedScrollDispatcher()) }
val scrollLogic = rememberUpdatedState(
ScrollingLogic(orientation, reverseDirection, nestedScrollDispatcher, controller, fling)
)
val nestedScrollConnection = remember(enabled) {
scrollableNestedScrollConnection(scrollLogic, enabled)
}
val draggableState = remember { ScrollDraggableState(scrollLogic) }
return draggable(
draggableState,
orientation = orientation,
enabled = enabled,
interactionSource = interactionSource,
reverseDirection = false,
startDragImmediately = { controller.isScrollInProgress },
onDragStopped = { velocity ->
nestedScrollDispatcher.value.coroutineScope.launch {
scrollLogic.value.onDragStopped(velocity)
}
},
canDrag = { down -> down.type != PointerType.Mouse }
).nestedScroll(nestedScrollConnection, nestedScrollDispatcher.value)
}
private class ScrollingLogic(
val orientation: Orientation,
val reverseDirection: Boolean,
val nestedScrollDispatcher: State<NestedScrollDispatcher>,
val scrollableState: ScrollableState,
val flingBehavior: FlingBehavior
) {
fun Float.toOffset(): Offset = when {
this == 0f -> Offset.Zero
orientation == Horizontal -> Offset(this, 0f)
else -> Offset(0f, this)
}
fun Float.toVelocity(): Velocity =
if (orientation == Horizontal) Velocity(this, 0f) else Velocity(0f, this)
fun Offset.toFloat(): Float =
if (orientation == Horizontal) this.x else this.y
fun Velocity.toFloat(): Float =
if (orientation == Horizontal) this.x else this.y
fun Float.reverseIfNeeded(): Float = if (reverseDirection) this * -1 else this
fun ScrollScope.dispatchScroll(scrollDelta: Float, source: NestedScrollSource): Float {
val nestedScrollDispatcher = nestedScrollDispatcher.value
val preConsumedByParent = nestedScrollDispatcher
.dispatchPreScroll(scrollDelta.toOffset(), source)
val scrollAvailable = scrollDelta - preConsumedByParent.toFloat()
val consumed = scrollBy(scrollAvailable.reverseIfNeeded()).reverseIfNeeded()
val leftForParent = scrollAvailable - consumed
nestedScrollDispatcher.dispatchPostScroll(
consumed.toOffset(),
leftForParent.toOffset(),
source
)
return leftForParent
}
fun performRawScroll(scroll: Offset): Offset {
return if (scrollableState.isScrollInProgress) {
Offset.Zero
} else {
scrollableState.dispatchRawDelta(scroll.toFloat().reverseIfNeeded())
.reverseIfNeeded().toOffset()
}
}
fun performRelocationScroll(scroll: Offset): Offset {
nestedScrollDispatcher.value.coroutineScope.launch {
scrollableState.animateScrollBy(scroll.toFloat().reverseIfNeeded())
}
return scroll
}
suspend fun onDragStopped(axisVelocity: Float) {
val velocity = axisVelocity.toVelocity()
val preConsumedByParent = nestedScrollDispatcher.value.dispatchPreFling(velocity)
val available = velocity - preConsumedByParent
val velocityLeft = doFlingAnimation(available)
nestedScrollDispatcher.value.dispatchPostFling(available - velocityLeft, velocityLeft)
}
suspend fun doFlingAnimation(available: Velocity): Velocity {
var result: Velocity = available
scrollableState.scroll {
val outerScopeScroll: (Float) -> Float = { delta ->
delta - this.dispatchScroll(delta.reverseIfNeeded(), Fling).reverseIfNeeded()
}
val scope = object : ScrollScope {
override fun scrollBy(pixels: Float): Float {
return outerScopeScroll.invoke(pixels)
}
}
with(scope) {
with(flingBehavior) {
result = performFling(available.toFloat().reverseIfNeeded())
.reverseIfNeeded().toVelocity()
}
}
}
return result
}
}
private class ScrollDraggableState(
val scrollLogic: State<ScrollingLogic>
) : DraggableState, DragScope {
var latestScrollScope: ScrollScope = NoOpScrollScope
override fun dragBy(pixels: Float) {
with(scrollLogic.value) {
with(latestScrollScope) {
dispatchScroll(pixels, Drag)
}
}
}
override suspend fun drag(
dragPriority: MutatePriority,
block: suspend DragScope.() -> Unit
) {
scrollLogic.value.scrollableState.scroll(dragPriority) {
latestScrollScope = this
block()
}
}
override fun dispatchRawDelta(delta: Float) {
with(scrollLogic.value) { performRawScroll(delta.toOffset()) }
}
}
private val NoOpScrollScope: ScrollScope = object : ScrollScope {
override fun scrollBy(pixels: Float): Float = pixels
}
private fun scrollableNestedScrollConnection(
scrollLogic: State<ScrollingLogic>,
enabled: Boolean
): NestedScrollConnection = object : NestedScrollConnection {
override fun onPostScroll(
consumed: Offset,
available: Offset,
source: NestedScrollSource
): Offset = if (enabled) {
@Suppress("DEPRECATION")
when (source) {
Drag, Fling -> scrollLogic.value.performRawScroll(available)
@OptIn(ExperimentalComposeUiApi::class)
Relocate -> scrollLogic.value.performRelocationScroll(available)
else -> error("$source scroll not supported.")
}
} else {
Offset.Zero
}
override suspend fun onPostFling(
consumed: Velocity,
available: Velocity
): Velocity {
return if (enabled) {
val velocityLeft = scrollLogic.value.doFlingAnimation(available)
available - velocityLeft
} else {
Velocity.Zero
}
}
}
private class DefaultFlingBehavior(
private val flingDecay: DecayAnimationSpec<Float>
) : FlingBehavior {
override suspend fun ScrollScope.performFling(initialVelocity: Float): Float {
// come up with the better threshold, but we need it since spline curve gives us NaNs
return if (abs(initialVelocity) > 1f) {
var velocityLeft = initialVelocity
var lastValue = 0f
AnimationState(
initialValue = 0f,
initialVelocity = initialVelocity,
).animateDecay(flingDecay) {
val delta = value - lastValue
val consumed = scrollBy(delta)
lastValue = value
velocityLeft = this.velocity
// avoid rounding errors and stop if anything is unconsumed
if (abs(delta - consumed) > 0.5f) this.cancelAnimation()
}
velocityLeft
} else {
initialVelocity
}
}
}