commonMain.androidx.compose.foundation.gestures.snapping.LazyGridSnapLayoutInfoProvider.kt Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of foundation-desktop Show documentation
Higher level abstractions of the Compose UI primitives. This library is design system agnostic, providing the high-level building blocks for both application and design-system developers
There is a newer version: 1.8.0-alpha01
Show newest version
/*
 * Copyright 2022 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.snapping

import androidx.compose.foundation.gestures.FlingBehavior
import androidx.compose.foundation.gestures.Orientation
import androidx.compose.foundation.lazy.grid.LazyGridItemInfo
import androidx.compose.foundation.lazy.grid.LazyGridLayoutInfo
import androidx.compose.foundation.lazy.grid.LazyGridState
import androidx.compose.runtime.Composable
import androidx.compose.runtime.remember
import androidx.compose.ui.util.fastForEach
import kotlin.math.absoluteValue
import kotlin.math.sign

/**
 * A [SnapLayoutInfoProvider] for LazyGrids.
 *
 * @param lazyGridState The [LazyGridState] with information about the current state of the grid
 * @param snapPosition The desired positioning of the snapped item within the main layout.
 * This position should be considered with regards to the start edge of the item and the placement
 * within the viewport.
 *
 * @return A [SnapLayoutInfoProvider] that can be used with [snapFlingBehavior]
 */
fun SnapLayoutInfoProvider(
    lazyGridState: LazyGridState,
    snapPosition: SnapPosition = SnapPosition.Center
) = object : SnapLayoutInfoProvider {
    private val layoutInfo: LazyGridLayoutInfo
        get() = lazyGridState.layoutInfo

    private val averageItemSize: Int
        get() {
            val layoutInfo = layoutInfo
            return if (layoutInfo.visibleItemsInfo.isEmpty()) {
                0
            } else {
                val numberOfItems = layoutInfo.visibleItemsInfo.size
                layoutInfo.visibleItemsInfo.sumOf {
                    it.sizeOnMainAxis(layoutInfo.orientation)
                } / numberOfItems
            }
        }

    override fun calculateApproachOffset(velocity: Float, decayOffset: Float): Float {
        return (decayOffset.absoluteValue - averageItemSize)
            .coerceAtLeast(0.0f) * decayOffset.sign
    }

    override fun calculateSnapOffset(
        velocity: Float
    ): Float {
        var distanceFromItemBeforeTarget = Float.NEGATIVE_INFINITY
        var distanceFromItemAfterTarget = Float.POSITIVE_INFINITY

        layoutInfo.visibleItemsInfo.fastForEach { item ->
            val distance =
                calculateDistanceToDesiredSnapPosition(
                    mainAxisViewPortSize = layoutInfo.singleAxisViewportSize,
                    beforeContentPadding = layoutInfo.beforeContentPadding,
                    afterContentPadding = layoutInfo.afterContentPadding,
                    itemSize = item.sizeOnMainAxis(orientation = layoutInfo.orientation),
                    itemOffset = item.offsetOnMainAxis(orientation = layoutInfo.orientation),
                    itemIndex = item.index,
                    snapPosition = snapPosition,
                    itemCount = layoutInfo.totalItemsCount
                )

            // Find item that is closest to the center
            if (distance <= 0 && distance > distanceFromItemBeforeTarget) {
                distanceFromItemBeforeTarget = distance
            }

            // Find item that is closest to center, but after it
            if (distance >= 0 && distance < distanceFromItemAfterTarget) {
                distanceFromItemAfterTarget = distance
            }
        }

        return calculateFinalOffset(
            with(lazyGridState.density) { calculateFinalSnappingItem(velocity) },
            distanceFromItemBeforeTarget,
            distanceFromItemAfterTarget
        )
    }
}

/**
 * Create and remember a FlingBehavior for decayed snapping in Lazy Grids. This will snap
 * the item according to [snapPosition].
 *
 * @param lazyGridState The [LazyGridState] from the LazyGrid where this [FlingBehavior] will
 * be used.
 * @param snapPosition The desired positioning of the snapped item within the main layout.
 * This position should be considered with regards to the start edge of the item and the placement
 * within the viewport.
 */
@Composable
fun rememberSnapFlingBehavior(
    lazyGridState: LazyGridState,
    snapPosition: SnapPosition = SnapPosition.Center
): FlingBehavior {
    val snappingLayout =
        remember(lazyGridState) { SnapLayoutInfoProvider(lazyGridState, snapPosition) }
    return rememberSnapFlingBehavior(snappingLayout)
}

internal val LazyGridLayoutInfo.singleAxisViewportSize: Int
    get() = if (orientation == Orientation.Vertical) {
        viewportSize.height
    } else {
        viewportSize.width
    }

internal fun LazyGridItemInfo.sizeOnMainAxis(orientation: Orientation): Int {
    return if (orientation == Orientation.Vertical) {
        size.height
    } else {
        size.width
    }
}

internal fun LazyGridItemInfo.offsetOnMainAxis(orientation: Orientation): Int {
    return if (orientation == Orientation.Vertical) {
        offset.y
    } else {
        offset.x
    }
}