/*
* 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.lazy
import androidx.compose.foundation.lazy.layout.LazyLayoutPlaceable
import androidx.compose.ui.Alignment
import androidx.compose.ui.layout.Placeable
import androidx.compose.ui.unit.IntOffset
import androidx.compose.ui.unit.LayoutDirection
import androidx.compose.ui.util.fastForEach
/**
* Represents one measured item of the lazy list. It can in fact consist of multiple placeables
* if the user emit multiple layout nodes in the item callback.
*/
internal class LazyMeasuredItem(
val index: Int,
private val placeables: Array<LazyLayoutPlaceable>,
private val isVertical: Boolean,
private val horizontalAlignment: Alignment.Horizontal?,
private val verticalAlignment: Alignment.Vertical?,
private val layoutDirection: LayoutDirection,
private val reverseLayout: Boolean,
private val startContentPadding: Int,
private val endContentPadding: Int,
/**
* Extra spacing to be added to [size] aside from the sum of the [placeables] size. It
* is usually representing the spacing after the item.
*/
private val spacing: Int,
val key: Any
) {
/**
* Sum of the main axis sizes of all the inner placeables.
*/
val size: Int
/**
* Sum of the main axis sizes of all the inner placeables and [spacing].
*/
val sizeWithSpacings: Int
/**
* Max of the cross axis sizes of all the inner placeables.
*/
val crossAxisSize: Int
init {
var mainAxisSize = 0
var maxCrossAxis = 0
placeables.forEach {
val placeable = it.placeable
mainAxisSize += if (isVertical) placeable.height else placeable.width
maxCrossAxis =
maxOf(maxCrossAxis, if (!isVertical) placeable.height else placeable.width)
}
size = mainAxisSize
sizeWithSpacings = size + spacing
crossAxisSize = maxCrossAxis
}
/**
* Calculates positions for the inner placeables at [offset] main axis position. [layoutWidth]
* and [layoutHeight] should be provided to not place placeables which are ended up outside of
* the viewport (for example one item consist of 2 placeables, and the first one is not going
* to be visible, so we don't place it as an optimization, but place the second one).
* If [reverseOrder] is true the inner placeables would be placed in the inverted order.
*/
fun position(
offset: Int,
layoutWidth: Int,
layoutHeight: Int
): LazyListPositionedItem {
val wrappers = mutableListOf<LazyListPlaceableWrapper>()
val mainAxisLayoutSize = if (isVertical) layoutHeight else layoutWidth
var mainAxisOffset = if (reverseLayout) {
mainAxisLayoutSize - offset - size
} else {
offset
}
var index = if (reverseLayout) placeables.lastIndex else 0
while (if (reverseLayout) index >= 0 else index < placeables.size) {
val it = placeables[index].placeable
val addIndex = if (reverseLayout) 0 else wrappers.size
val placeableOffset = if (isVertical) {
val x = requireNotNull(horizontalAlignment)
.align(it.width, layoutWidth, layoutDirection)
IntOffset(x, mainAxisOffset)
} else {
val y = requireNotNull(verticalAlignment).align(it.height, layoutHeight)
IntOffset(mainAxisOffset, y)
}
mainAxisOffset += if (isVertical) it.height else it.width
wrappers.add(
addIndex,
LazyListPlaceableWrapper(placeableOffset, it, placeables[index].parentData)
)
if (reverseLayout) index-- else index++
}
return LazyListPositionedItem(
offset = offset,
index = this.index,
key = key,
size = size,
sizeWithSpacings = sizeWithSpacings,
minMainAxisOffset = -startContentPadding,
maxMainAxisOffset = mainAxisLayoutSize + endContentPadding,
isVertical = isVertical,
wrappers = wrappers
)
}
}
internal class LazyListPositionedItem(
override val offset: Int,
override val index: Int,
override val key: Any,
override val size: Int,
val sizeWithSpacings: Int,
private val minMainAxisOffset: Int,
private val maxMainAxisOffset: Int,
private val isVertical: Boolean,
private val wrappers: List<LazyListPlaceableWrapper>
) : LazyListItemInfo {
fun place(
scope: Placeable.PlacementScope,
) = with(scope) {
wrappers.fastForEach { wrapper ->
val offset = wrapper.offset
val placeable = wrapper.placeable
if (offset.mainAxis + placeable.mainAxisSize > minMainAxisOffset &&
offset.mainAxis < maxMainAxisOffset
) {
if (isVertical) {
placeable.placeWithLayer(offset)
} else {
placeable.placeRelativeWithLayer(offset)
}
}
}
}
private val IntOffset.mainAxis get() = if (isVertical) y else x
private val Placeable.mainAxisSize get() = if (isVertical) height else width
}
internal class LazyListPlaceableWrapper(
val offset: IntOffset,
val placeable: Placeable,
val parentData: Any?
)