commonMain.androidx.compose.foundation.gestures.snapping.SnapPositionInLayout.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 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.gestures.snapping

import androidx.compose.foundation.ExperimentalFoundationApi
import androidx.compose.ui.unit.Density

/**
 * Describes the general positioning of a given snap item in its containing layout.
 */
@ExperimentalFoundationApi
fun interface SnapPositionInLayout {
    /**
     * Calculates an offset positioning between a container and an element within this container.
     * The offset calculation is the necessary diff that should be applied to the item offset to
     * align the item with a position within the container. As a base line, if we wanted to align
     * the start of the container and the start of the item, we would return 0 in this function.
     */
    fun Density.position(layoutSize: Int, itemSize: Int, itemIndex: Int): Int

    companion object {
        /**
         * Aligns the center of the item with the center of the containing layout.
         */
        val CenterToCenter =
            SnapPositionInLayout { layoutSize, itemSize, _ -> layoutSize / 2 - itemSize / 2 }
    }
}

@OptIn(ExperimentalFoundationApi::class)
internal fun Density.calculateDistanceToDesiredSnapPosition(
    mainAxisViewPortSize: Int,
    beforeContentPadding: Int,
    afterContentPadding: Int,
    itemSize: Int,
    itemOffset: Int,
    itemIndex: Int,
    snapPositionInLayout: SnapPositionInLayout
): Float {
    val containerSize = mainAxisViewPortSize - beforeContentPadding - afterContentPadding

    val desiredDistance = with(snapPositionInLayout) {
        position(containerSize, itemSize, itemIndex)
    }.toFloat()

    return itemOffset - desiredDistance
}