/*
* Copyright 2021 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.lazy
import androidx.compose.animation.core.Animatable
import androidx.compose.animation.core.Spring
import androidx.compose.animation.core.SpringSpec
import androidx.compose.animation.core.VectorConverter
import androidx.compose.animation.core.VisibilityThreshold
import androidx.compose.animation.core.spring
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.setValue
import androidx.compose.ui.unit.IntOffset
import androidx.compose.ui.util.fastAny
import androidx.compose.ui.util.fastForEach
import androidx.compose.ui.util.fastForEachIndexed
import kotlinx.coroutines.CancellationException
import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.launch
/**
* Handles the item placement animations when it is set via [LazyItemScope.animateItemPlacement].
*
* This class is responsible for detecting when item position changed, figuring our start/end
* offsets and starting the animations.
*/
internal class LazyListItemPlacementAnimator(
private val scope: CoroutineScope,
private val isVertical: Boolean
) {
// state containing an animation and all relevant info for each item.
private val keyToItemInfoMap = mutableMapOf<Any, ItemInfo>()
// snapshot of the key to index map used for the last measuring.
private var keyToIndexMap: Map<Any, Int> = emptyMap()
// keeps the first and the last items positioned in the viewport and their visible part sizes.
private var viewportStartItemIndex = -1
private var viewportStartItemNotVisiblePartSize = 0
private var viewportEndItemIndex = -1
private var viewportEndItemNotVisiblePartSize = 0
// stored to not allocate it every pass.
private val positionedKeys = mutableSetOf<Any>()
/**
* Should be called after the measuring so we can detect position changes and start animations.
*
* Note that this method can compose new item and add it into the [positionedItems] list.
*/
fun onMeasured(
consumedScroll: Int,
layoutWidth: Int,
layoutHeight: Int,
reverseLayout: Boolean,
positionedItems: MutableList<LazyListPositionedItem>,
itemProvider: LazyMeasuredItemProvider
) {
if (!positionedItems.fastAny { it.hasAnimations }) {
// no animations specified - no work needed
reset()
return
}
val mainAxisLayoutSize = if (isVertical) layoutHeight else layoutWidth
// the consumed scroll is considered as a delta we don't need to animate
val notAnimatableDelta = (if (reverseLayout) -consumedScroll else consumedScroll).toOffset()
val newFirstItem = positionedItems.first()
val newLastItem = positionedItems.last()
var totalItemsSize = 0
// update known indexes and calculate the average size
positionedItems.fastForEach { item ->
keyToItemInfoMap[item.key]?.index = item.index
totalItemsSize += item.sizeWithSpacings
}
val averageItemSize = totalItemsSize / positionedItems.size
positionedKeys.clear()
// iterate through the items which are visible (without animated offsets)
positionedItems.fastForEach { item ->
positionedKeys.add(item.key)
val itemInfo = keyToItemInfoMap[item.key]
if (itemInfo == null) {
// there is no state associated with this item yet
if (item.hasAnimations) {
val newItemInfo = ItemInfo(item.index)
val previousIndex = keyToIndexMap[item.key]
val firstPlaceableOffset = item.getOffset(0)
val firstPlaceableSize = item.getMainAxisSize(0)
val targetFirstPlaceableOffsetMainAxis = if (previousIndex == null) {
// it is a completely new item. no animation is needed
firstPlaceableOffset.mainAxis
} else {
val fallback = if (!reverseLayout) {
firstPlaceableOffset.mainAxis
} else {
firstPlaceableOffset.mainAxis - item.sizeWithSpacings +
firstPlaceableSize
}
calculateExpectedOffset(
index = previousIndex,
sizeWithSpacings = item.sizeWithSpacings,
averageItemsSize = averageItemSize,
scrolledBy = notAnimatableDelta,
fallback = fallback,
reverseLayout = reverseLayout,
mainAxisLayoutSize = mainAxisLayoutSize,
visibleItems = positionedItems
) + if (reverseLayout) {
item.size - firstPlaceableSize
} else {
0
}
}
val targetFirstPlaceableOffset = if (isVertical) {
firstPlaceableOffset.copy(y = targetFirstPlaceableOffsetMainAxis)
} else {
firstPlaceableOffset.copy(x = targetFirstPlaceableOffsetMainAxis)
}
// populate placeable info list
repeat(item.placeablesCount) { placeableIndex ->
val diffToFirstPlaceableOffset =
item.getOffset(placeableIndex) - firstPlaceableOffset
newItemInfo.placeables.add(
PlaceableInfo(
targetFirstPlaceableOffset + diffToFirstPlaceableOffset,
item.getMainAxisSize(placeableIndex)
)
)
}
keyToItemInfoMap[item.key] = newItemInfo
startAnimationsIfNeeded(item, newItemInfo)
}
} else {
if (item.hasAnimations) {
// apply new not animatable offset
itemInfo.notAnimatableDelta += notAnimatableDelta
startAnimationsIfNeeded(item, itemInfo)
} else {
// no animation, clean up if needed
keyToItemInfoMap.remove(item.key)
}
}
}
// previously we were animating items which are visible in the end state so we had to
// compare the current state with the state used for the previous measuring.
// now we will animate disappearing items so the current state is their starting state
// so we can update current viewport start/end items
if (!reverseLayout) {
viewportStartItemIndex = newFirstItem.index
viewportStartItemNotVisiblePartSize = newFirstItem.offset
viewportEndItemIndex = newLastItem.index
viewportEndItemNotVisiblePartSize =
newLastItem.offset + newLastItem.sizeWithSpacings - mainAxisLayoutSize
} else {
viewportStartItemIndex = newLastItem.index
viewportStartItemNotVisiblePartSize =
mainAxisLayoutSize - newLastItem.offset - newLastItem.size
viewportEndItemIndex = newFirstItem.index
viewportEndItemNotVisiblePartSize =
-newFirstItem.offset + (newFirstItem.sizeWithSpacings - newFirstItem.size)
}
val iterator = keyToItemInfoMap.iterator()
while (iterator.hasNext()) {
val entry = iterator.next()
if (!positionedKeys.contains(entry.key)) {
// found an item which was in our map previously but is not a part of the
// positionedItems now
val itemInfo = entry.value
// apply new not animatable delta for this item
itemInfo.notAnimatableDelta += notAnimatableDelta
val index = itemProvider.keyToIndexMap[entry.key]
// whether at least one placeable is within the viewport bounds.
// this usually means that we will start animation for it right now
val withinBounds = itemInfo.placeables.fastAny {
val currentTarget = it.targetOffset + itemInfo.notAnimatableDelta
currentTarget.mainAxis + it.size > 0 &&
currentTarget.mainAxis < mainAxisLayoutSize
}
// whether the animation associated with the item has been finished
val isFinished = !itemInfo.placeables.fastAny { it.inProgress }
if ((!withinBounds && isFinished) ||
index == null ||
itemInfo.placeables.isEmpty()
) {
iterator.remove()
} else {
val measuredItem = itemProvider.getAndMeasure(DataIndex(index))
// calculate the target offset for the animation.
val absoluteTargetOffset = calculateExpectedOffset(
index = index,
sizeWithSpacings = measuredItem.sizeWithSpacings,
averageItemsSize = averageItemSize,
scrolledBy = notAnimatableDelta,
fallback = mainAxisLayoutSize,
reverseLayout = reverseLayout,
mainAxisLayoutSize = mainAxisLayoutSize,
visibleItems = positionedItems
)
val targetOffset = if (reverseLayout) {
mainAxisLayoutSize - absoluteTargetOffset - measuredItem.size
} else {
absoluteTargetOffset
}
val item = measuredItem.position(targetOffset, layoutWidth, layoutHeight)
positionedItems.add(item)
startAnimationsIfNeeded(item, itemInfo)
}
}
}
keyToIndexMap = itemProvider.keyToIndexMap
}
/**
* Returns the current animated item placement offset. By calling it only during the layout
* phase we can skip doing remeasure on every animation frame.
*/
fun getAnimatedOffset(
key: Any,
placeableIndex: Int,
minOffset: Int,
maxOffset: Int,
rawOffset: IntOffset
): IntOffset {
val itemInfo = keyToItemInfoMap[key] ?: return rawOffset
val item = itemInfo.placeables[placeableIndex]
val currentValue = item.animatedOffset.value + itemInfo.notAnimatableDelta
val currentTarget = item.targetOffset + itemInfo.notAnimatableDelta
// cancel the animation if it is fully out of the bounds.
if (item.inProgress &&
((currentTarget.mainAxis < minOffset && currentValue.mainAxis < minOffset) ||
(currentTarget.mainAxis > maxOffset && currentValue.mainAxis > maxOffset))
) {
scope.launch {
item.animatedOffset.snapTo(item.targetOffset)
item.inProgress = false
}
}
return currentValue
}
/**
* Should be called when the animations are not needed for the next positions change,
* for example when we snap to a new position.
*/
fun reset() {
keyToItemInfoMap.clear()
keyToIndexMap = emptyMap()
viewportStartItemIndex = -1
viewportStartItemNotVisiblePartSize = 0
viewportEndItemIndex = -1
viewportEndItemNotVisiblePartSize = 0
}
/**
* Estimates the outside of the viewport offset for the item. Used to understand from
* where to start animation for the item which wasn't visible previously or where it should
* end for the item which is not going to be visible in the end.
*/
private fun calculateExpectedOffset(
index: Int,
sizeWithSpacings: Int,
averageItemsSize: Int,
scrolledBy: IntOffset,
reverseLayout: Boolean,
mainAxisLayoutSize: Int,
fallback: Int,
visibleItems: List<LazyListPositionedItem>
): Int {
val afterViewportEnd =
if (!reverseLayout) viewportEndItemIndex < index else viewportEndItemIndex > index
val beforeViewportStart =
if (!reverseLayout) viewportStartItemIndex > index else viewportStartItemIndex < index
return when {
afterViewportEnd -> {
var itemsSizes = 0
// add sizes of the items between the last visible one and this one.
val range = if (!reverseLayout) {
viewportEndItemIndex + 1 until index
} else {
index + 1 until viewportEndItemIndex
}
for (i in range) {
itemsSizes += visibleItems.getItemSize(
itemIndex = i,
fallback = averageItemsSize
)
}
mainAxisLayoutSize + viewportEndItemNotVisiblePartSize + itemsSizes +
scrolledBy.mainAxis
}
beforeViewportStart -> {
// add the size of this item as we need the start offset of this item.
var itemsSizes = sizeWithSpacings
// add sizes of the items between the first visible one and this one.
val range = if (!reverseLayout) {
index + 1 until viewportStartItemIndex
} else {
viewportStartItemIndex + 1 until index
}
for (i in range) {
itemsSizes += visibleItems.getItemSize(
itemIndex = i,
fallback = averageItemsSize
)
}
viewportStartItemNotVisiblePartSize - itemsSizes + scrolledBy.mainAxis
}
else -> {
fallback
}
}
}
private fun List<LazyListPositionedItem>.getItemSize(itemIndex: Int, fallback: Int): Int {
if (isEmpty() || itemIndex < first().index || itemIndex > last().index) return fallback
if ((itemIndex - first().index) < (last().index - itemIndex)) {
for (index in indices) {
val item = get(index)
if (item.index == itemIndex) return item.sizeWithSpacings
if (item.index > itemIndex) break
}
} else {
for (index in lastIndex downTo 0) {
val item = get(index)
if (item.index == itemIndex) return item.sizeWithSpacings
if (item.index < itemIndex) break
}
}
return fallback
}
private fun startAnimationsIfNeeded(item: LazyListPositionedItem, itemInfo: ItemInfo) {
// first we make sure our item info is up to date (has the item placeables count)
while (itemInfo.placeables.size > item.placeablesCount) {
itemInfo.placeables.removeLast()
}
while (itemInfo.placeables.size < item.placeablesCount) {
val newPlaceableInfoIndex = itemInfo.placeables.size
val rawOffset = item.getOffset(newPlaceableInfoIndex)
itemInfo.placeables.add(
PlaceableInfo(
rawOffset - itemInfo.notAnimatableDelta,
item.getMainAxisSize(newPlaceableInfoIndex)
)
)
}
itemInfo.placeables.fastForEachIndexed { index, placeableInfo ->
val currentTarget = placeableInfo.targetOffset + itemInfo.notAnimatableDelta
val currentOffset = item.getOffset(index)
placeableInfo.size = item.getMainAxisSize(index)
val animationSpec = item.getAnimationSpec(index)
if (currentTarget != currentOffset) {
placeableInfo.targetOffset = currentOffset - itemInfo.notAnimatableDelta
if (animationSpec != null) {
placeableInfo.inProgress = true
scope.launch {
val finalSpec = if (placeableInfo.animatedOffset.isRunning) {
// when interrupted, use the default spring, unless the spec is a spring.
if (animationSpec is SpringSpec<IntOffset>) animationSpec else
InterruptionSpec
} else {
animationSpec
}
try {
placeableInfo.animatedOffset.animateTo(
placeableInfo.targetOffset,
finalSpec
)
placeableInfo.inProgress = false
} catch (_: CancellationException) {
// we don't reset inProgress in case of cancellation as it means
// there is a new animation started which would reset it later
}
}
}
}
}
}
private fun Int.toOffset() =
IntOffset(if (isVertical) 0 else this, if (!isVertical) 0 else this)
private val IntOffset.mainAxis get() = if (isVertical) y else x
}
private class ItemInfo(var index: Int) {
var notAnimatableDelta: IntOffset = IntOffset.Zero
val placeables = mutableListOf<PlaceableInfo>()
}
private class PlaceableInfo(
initialOffset: IntOffset,
var size: Int
) {
val animatedOffset = Animatable(initialOffset, IntOffset.VectorConverter)
var targetOffset: IntOffset = initialOffset
var inProgress by mutableStateOf(false)
}
/**
* We switch to this spec when a duration based animation is being interrupted.
*/
private val InterruptionSpec = spring(
stiffness = Spring.StiffnessMediumLow,
visibilityThreshold = IntOffset.VisibilityThreshold
)