/*
* 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.staggeredgrid
import androidx.compose.foundation.ExperimentalFoundationApi
import androidx.compose.foundation.gestures.ScrollScope
import androidx.compose.foundation.lazy.layout.LazyAnimateScrollScope
import androidx.compose.ui.unit.Density
import androidx.compose.ui.util.fastSumBy
@ExperimentalFoundationApi
internal class LazyStaggeredGridAnimateScrollScope(
private val state: LazyStaggeredGridState
) : LazyAnimateScrollScope {
override val density: Density get() = state.density
override val firstVisibleItemIndex: Int get() = state.firstVisibleItemIndex
override val firstVisibleItemScrollOffset: Int get() = state.firstVisibleItemScrollOffset
override val lastVisibleItemIndex: Int
get() = state.layoutInfo.visibleItemsInfo.lastOrNull()?.index ?: 0
override val itemCount: Int get() = state.layoutInfo.totalItemsCount
override fun getTargetItemOffset(index: Int): Int? =
state.layoutInfo.findVisibleItem(index)?.offset?.let {
if (state.isVertical) it.y else it.x
}
override fun ScrollScope.snapToItem(index: Int, scrollOffset: Int) {
with(state) {
snapToItemInternal(index, scrollOffset)
}
}
override fun expectedDistanceTo(index: Int, targetScrollOffset: Int): Float {
val visibleItems = state.layoutInfo.visibleItemsInfo
val itemSizeSum = visibleItems
.fastSumBy { if (state.isVertical) it.size.height else it.size.width }
val averageMainAxisItemSize = itemSizeSum / (visibleItems.size * state.laneCount)
val indexesDiff = index - firstVisibleItemIndex
return (averageMainAxisItemSize * indexesDiff).toFloat() +
targetScrollOffset - firstVisibleItemScrollOffset
}
override val numOfItemsForTeleport: Int get() = 100 * state.laneCount
override suspend fun scroll(block: suspend ScrollScope.() -> Unit) {
state.scroll(block = block)
}
}