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

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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
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/*
 * 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
    }
}