ScalingLazyListLayoutInfo.kt

/*
 * 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.wear.compose.material

import androidx.compose.foundation.gestures.Orientation
import androidx.compose.ui.unit.IntSize

/**
 * Contains useful information about the currently displayed layout state of [ScalingLazyColumn].
 * For example you can get the list of currently displayed item.
 *
 * Use [ScalingLazyListState.layoutInfo] to retrieve this
 */
public sealed interface ScalingLazyListLayoutInfo {
    /**
     * The list of [ScalingLazyListItemInfo] representing all the currently visible items.
     */
    val visibleItemsInfo: List<ScalingLazyListItemInfo>

    /**
     * The start offset of the layout's viewport in pixels. You can think of it as a minimum offset
     * which would be visible. Usually it is 0, but it can be negative if non-zero
     * [beforeContentPadding] was applied as the content displayed in the content padding area is
     * still visible.
     *
     * You can use it to understand what items from [visibleItemsInfo] are fully visible.
     */
    val viewportStartOffset: Int

    /**
     * The end offset of the layout's viewport in pixels. You can think of it as a maximum offset
     * which would be visible. It is the size of the scaling lazy list layout minus
     * [beforeContentPadding].
     *
     * You can use it to understand what items from [visibleItemsInfo] are fully visible.
     */
    val viewportEndOffset: Int

    /**
     * The total count of items passed to [ScalingLazyColumn].
     */
    val totalItemsCount: Int

    /**
     * The size of the viewport in pixels. It is the scaling lazy list layout size including all the
     * content paddings.
     */
    val viewportSize: IntSize

    /**
     * The orientation of the scaling lazy list.
     */
    val orientation: Orientation

    /**
     * True if the direction of scrolling and layout is reversed.
     */
    val reverseLayout: Boolean

    /**
     * The content padding in pixels applied before the first item in the direction of scrolling.
     * For example it is a top content padding for ScalingLazyColumn with reverseLayout set to
     * false.
     */
    val beforeContentPadding: Int

    /**
     * The content padding in pixels applied after the last item in the direction of scrolling.
     * For example it is a bottom content padding for ScalingLazyColumn with reverseLayout set to
     * false.
     */
    val afterContentPadding: Int

    /**
     * The auto centering padding in pixels applied before the first item in the direction of
     * scrolling. For example it is a top auto centering padding for ScalingLazyColumn with
     * reverseLayout set to false.
     */
    val beforeAutoCenteringPadding: Int

    /**
     * The auto centering padding in pixels applied after the last item in the direction of
     * scrolling. For example it is a bottom auto centering padding for ScalingLazyColumn with
     * reverseLayout set to false.
     */
    val afterAutoCenteringPadding: Int
}