MeasuredPage.kt
/*
* Copyright 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 androidx.compose.foundation.pager
import androidx.compose.foundation.gestures.Orientation
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
internal class MeasuredPage(
val index: Int,
val size: Int,
val placeables: List<Placeable>,
val visualOffset: IntOffset,
val key: Any,
val orientation: Orientation,
val horizontalAlignment: Alignment.Horizontal?,
val verticalAlignment: Alignment.Vertical?,
val layoutDirection: LayoutDirection,
val reverseLayout: Boolean,
val beforeContentPadding: Int,
val afterContentPadding: Int,
) {
val crossAxisSize: Int
init {
var maxCrossAxis = 0
placeables.fastForEach {
maxCrossAxis = maxOf(
maxCrossAxis,
if (orientation != Orientation.Vertical) it.height else it.width
)
}
crossAxisSize = maxCrossAxis
}
fun position(
offset: Int,
layoutWidth: Int,
layoutHeight: Int
): PositionedPage {
val wrappers = mutableListOf<PagerPlaceableWrapper>()
val mainAxisLayoutSize =
if (orientation == Orientation.Vertical) 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]
val addIndex = if (reverseLayout) 0 else wrappers.size
val placeableOffset = if (orientation == Orientation.Vertical) {
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 (orientation == Orientation.Vertical) it.height else it.width
wrappers.add(
addIndex,
PagerPlaceableWrapper(placeableOffset, it, placeables[index].parentData)
)
if (reverseLayout) index-- else index++
}
return PositionedPage(
offset = offset,
index = this.index,
key = key,
orientation = orientation,
wrappers = wrappers,
visualOffset = visualOffset,
)
}
}
internal class PagerPlaceableWrapper(
val offset: IntOffset,
val placeable: Placeable,
val parentData: Any?
)