| /* |
| * 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.grid |
| |
| import androidx.compose.foundation.ExperimentalFoundationApi |
| import androidx.compose.foundation.gestures.Orientation |
| import androidx.compose.foundation.layout.Arrangement |
| import androidx.compose.ui.layout.MeasureResult |
| import androidx.compose.ui.layout.Placeable |
| import androidx.compose.ui.unit.Constraints |
| import androidx.compose.ui.unit.Density |
| import androidx.compose.ui.unit.LayoutDirection |
| import androidx.compose.ui.unit.constrainHeight |
| import androidx.compose.ui.unit.constrainWidth |
| import androidx.compose.ui.util.fastForEach |
| import kotlin.math.abs |
| import kotlin.math.roundToInt |
| import kotlin.math.sign |
| |
| /** |
| * Measures and calculates the positions for the currently visible items. The result is produced |
| * as a [LazyGridMeasureResult] which contains all the calculations. |
| */ |
| @OptIn(ExperimentalFoundationApi::class) |
| internal fun measureLazyGrid( |
| itemsCount: Int, |
| lineProvider: LazyMeasuredLineProvider, |
| mainAxisMaxSize: Int, |
| beforeContentPadding: Int, |
| afterContentPadding: Int, |
| firstVisibleLineIndex: LineIndex, |
| firstVisibleLineScrollOffset: Int, |
| scrollToBeConsumed: Float, |
| constraints: Constraints, |
| isVertical: Boolean, |
| verticalArrangement: Arrangement.Vertical?, |
| horizontalArrangement: Arrangement.Horizontal?, |
| reverseLayout: Boolean, |
| density: Density, |
| layoutDirection: LayoutDirection, |
| // placementAnimator: LazyListItemPlacementAnimator, |
| layout: (Int, Int, Placeable.PlacementScope.() -> Unit) -> MeasureResult |
| ): LazyGridMeasureResult { |
| require(beforeContentPadding >= 0) |
| require(afterContentPadding >= 0) |
| if (itemsCount <= 0) { |
| // empty data set. reset the current scroll and report zero size |
| return LazyGridMeasureResult( |
| firstVisibleLine = null, |
| firstVisibleLineScrollOffset = 0, |
| canScrollForward = false, |
| consumedScroll = 0f, |
| measureResult = layout(constraints.minWidth, constraints.minHeight) {}, |
| visibleItemsInfo = emptyList(), |
| viewportStartOffset = -beforeContentPadding, |
| viewportEndOffset = afterContentPadding, |
| totalItemsCount = 0, |
| reverseLayout = reverseLayout, |
| orientation = if (isVertical) Orientation.Vertical else Orientation.Horizontal, |
| ) |
| } else { |
| var currentFirstLineIndex = firstVisibleLineIndex |
| var currentFirstLineScrollOffset = firstVisibleLineScrollOffset |
| |
| // represents the real amount of scroll we applied as a result of this measure pass. |
| var scrollDelta = scrollToBeConsumed.roundToInt() |
| |
| // applying the whole requested scroll offset. we will figure out if we can't consume |
| // all of it later |
| currentFirstLineScrollOffset -= scrollDelta |
| |
| // if the current scroll offset is less than minimally possible |
| if (currentFirstLineIndex == LineIndex(0) && currentFirstLineScrollOffset < 0) { |
| scrollDelta += currentFirstLineScrollOffset |
| currentFirstLineScrollOffset = 0 |
| } |
| |
| // this will contain all the MeasuredItems representing the visible lines |
| val visibleLines = mutableListOf<LazyMeasuredLine>() |
| |
| // include the start padding so we compose items in the padding area. before starting |
| // scrolling forward we would remove it back |
| currentFirstLineScrollOffset -= beforeContentPadding |
| |
| // define min and max offsets (min offset currently includes beforeContentPadding) |
| val minOffset = -beforeContentPadding |
| val maxOffset = mainAxisMaxSize |
| |
| // we had scrolled backward or we compose items in the start padding area, which means |
| // items before current firstLineScrollOffset should be visible. compose them and update |
| // firstLineScrollOffset |
| while (currentFirstLineScrollOffset < 0 && currentFirstLineIndex > LineIndex(0)) { |
| val previous = LineIndex(currentFirstLineIndex.value - 1) |
| val measuredLine = lineProvider.getAndMeasure(previous) |
| visibleLines.add(0, measuredLine) |
| currentFirstLineScrollOffset += measuredLine.sizeWithSpacings |
| currentFirstLineIndex = previous |
| } |
| // if we were scrolled backward, but there were not enough lines before. this means |
| // not the whole scroll was consumed |
| if (currentFirstLineScrollOffset < minOffset) { |
| scrollDelta += currentFirstLineScrollOffset |
| currentFirstLineScrollOffset = minOffset |
| } |
| |
| // neutralize previously added start padding as we stopped filling the before content padding |
| currentFirstLineScrollOffset += beforeContentPadding |
| |
| var index = currentFirstLineIndex |
| val maxMainAxis = maxOffset + afterContentPadding |
| var mainAxisUsed = -currentFirstLineScrollOffset |
| |
| // first we need to skip lines we already composed while composing backward |
| visibleLines.fastForEach { |
| index++ |
| mainAxisUsed += it.sizeWithSpacings |
| } |
| |
| // then composing visible lines forward until we fill the whole viewport |
| while (mainAxisUsed <= maxMainAxis) { |
| val measuredLine = lineProvider.getAndMeasure(index) |
| if (measuredLine.isEmpty()) { |
| --index |
| break |
| } |
| |
| mainAxisUsed += measuredLine.sizeWithSpacings |
| if (mainAxisUsed <= minOffset) { |
| // this line is offscreen and will not be placed. advance firstVisibleLineIndex |
| currentFirstLineIndex = index + 1 |
| currentFirstLineScrollOffset -= measuredLine.sizeWithSpacings |
| } else { |
| visibleLines.add(measuredLine) |
| } |
| index++ |
| } |
| |
| // we didn't fill the whole viewport with lines starting from firstVisibleLineIndex. |
| // lets try to scroll back if we have enough lines before firstVisibleLineIndex. |
| if (mainAxisUsed < maxOffset) { |
| val toScrollBack = maxOffset - mainAxisUsed |
| currentFirstLineScrollOffset -= toScrollBack |
| mainAxisUsed += toScrollBack |
| while (currentFirstLineScrollOffset < 0 && currentFirstLineIndex > LineIndex(0)) { |
| val previousIndex = LineIndex(currentFirstLineIndex.value - 1) |
| val measuredLine = lineProvider.getAndMeasure(previousIndex) |
| visibleLines.add(0, measuredLine) |
| currentFirstLineScrollOffset += measuredLine.sizeWithSpacings |
| currentFirstLineIndex = previousIndex |
| } |
| scrollDelta += toScrollBack |
| if (currentFirstLineScrollOffset < 0) { |
| scrollDelta += currentFirstLineScrollOffset |
| mainAxisUsed += currentFirstLineScrollOffset |
| currentFirstLineScrollOffset = 0 |
| } |
| } |
| |
| // report the amount of pixels we consumed. scrollDelta can be smaller than |
| // scrollToBeConsumed if there were not enough lines to fill the offered space or it |
| // can be larger if lines were resized, or if, for example, we were previously |
| // displaying the line 15, but now we have only 10 lines in total in the data set. |
| val consumedScroll = if (scrollToBeConsumed.roundToInt().sign == scrollDelta.sign && |
| abs(scrollToBeConsumed.roundToInt()) >= abs(scrollDelta) |
| ) { |
| scrollDelta.toFloat() |
| } else { |
| scrollToBeConsumed |
| } |
| |
| // the initial offset for lines from visibleLines list |
| val visibleLinesScrollOffset = -currentFirstLineScrollOffset |
| var firstLine = visibleLines.firstOrNull() |
| |
| // even if we compose lines to fill before content padding we should ignore lines fully |
| // located there for the state's scroll position calculation (first line + first offset) |
| if (beforeContentPadding > 0) { |
| for (i in visibleLines.indices) { |
| val size = visibleLines[i].sizeWithSpacings |
| if (size <= currentFirstLineScrollOffset && i != visibleLines.lastIndex) { |
| currentFirstLineScrollOffset -= size |
| firstLine = visibleLines[i + 1] |
| } else { |
| break |
| } |
| } |
| } |
| |
| val layoutWidth = |
| if (isVertical) constraints.maxWidth else constraints.constrainWidth(mainAxisUsed) |
| val layoutHeight = |
| if (isVertical) constraints.constrainHeight(mainAxisUsed) else constraints.maxHeight |
| |
| val positionedItems = calculateItemsOffsets( |
| lines = visibleLines, |
| layoutWidth = layoutWidth, |
| layoutHeight = layoutHeight, |
| usedMainAxisSize = mainAxisUsed, |
| firstLineScrollOffset = visibleLinesScrollOffset, |
| isVertical = isVertical, |
| verticalArrangement = verticalArrangement, |
| horizontalArrangement = horizontalArrangement, |
| reverseLayout = reverseLayout, |
| density = density, |
| layoutDirection = layoutDirection |
| ) |
| |
| // placementAnimator.onMeasured( |
| // consumedScroll = consumedScroll.toInt(), |
| // layoutWidth = layoutWidth, |
| // layoutHeight = layoutHeight, |
| // reverseLayout = reverseLayout, |
| // positionedItems = positionedItems, |
| // lineProvider = lineProvider |
| // ) |
| |
| val maximumVisibleOffset = minOf(mainAxisUsed, mainAxisMaxSize) + afterContentPadding |
| |
| return LazyGridMeasureResult( |
| firstVisibleLine = firstLine, |
| firstVisibleLineScrollOffset = currentFirstLineScrollOffset, |
| canScrollForward = mainAxisUsed > maxOffset, |
| consumedScroll = consumedScroll, |
| measureResult = layout(layoutWidth, layoutHeight) { |
| positionedItems.fastForEach { it.place(this) } |
| }, |
| viewportStartOffset = -beforeContentPadding, |
| viewportEndOffset = maximumVisibleOffset, |
| visibleItemsInfo = positionedItems, |
| totalItemsCount = itemsCount, |
| reverseLayout = reverseLayout, |
| orientation = if (isVertical) Orientation.Vertical else Orientation.Horizontal |
| ) |
| } |
| } |
| |
| /** |
| * Calculates [LazyMeasuredLine]s offsets. |
| */ |
| @OptIn(ExperimentalFoundationApi::class) |
| private fun calculateItemsOffsets( |
| lines: List<LazyMeasuredLine>, |
| layoutWidth: Int, |
| layoutHeight: Int, |
| usedMainAxisSize: Int, |
| firstLineScrollOffset: Int, |
| isVertical: Boolean, |
| verticalArrangement: Arrangement.Vertical?, |
| horizontalArrangement: Arrangement.Horizontal?, |
| reverseLayout: Boolean, |
| density: Density, |
| layoutDirection: LayoutDirection |
| ): MutableList<LazyGridPositionedItem> { |
| val mainAxisLayoutSize = if (isVertical) layoutHeight else layoutWidth |
| val hasSpareSpace = usedMainAxisSize < mainAxisLayoutSize |
| if (hasSpareSpace) { |
| check(firstLineScrollOffset == 0) |
| } |
| |
| val positionedItems = ArrayList<LazyGridPositionedItem>(lines.size) |
| |
| if (hasSpareSpace) { |
| val linesCount = lines.size |
| val sizes = IntArray(linesCount) { index -> |
| val reverseLayoutAwareIndex = if (!reverseLayout) index else linesCount - index - 1 |
| lines[reverseLayoutAwareIndex].mainAxisSize |
| } |
| val offsets = IntArray(linesCount) { 0 } |
| if (isVertical) { |
| with(requireNotNull(verticalArrangement)) { |
| density.arrange(mainAxisLayoutSize, sizes, offsets) |
| } |
| } else { |
| with(requireNotNull(horizontalArrangement)) { |
| density.arrange(mainAxisLayoutSize, sizes, layoutDirection, offsets) |
| } |
| } |
| offsets.forEachIndexed { index, absoluteOffset -> |
| val reverseLayoutAwareIndex = if (!reverseLayout) index else linesCount - index - 1 |
| val line = lines[reverseLayoutAwareIndex] |
| val relativeOffset = if (reverseLayout) { |
| mainAxisLayoutSize - absoluteOffset - line.mainAxisSize |
| } else { |
| absoluteOffset |
| } |
| val addIndex = if (reverseLayout) 0 else positionedItems.size |
| positionedItems.addAll( |
| addIndex, |
| line.position(relativeOffset, layoutWidth, layoutHeight) |
| ) |
| } |
| } else { |
| var currentMainAxis = firstLineScrollOffset |
| lines.fastForEach { |
| positionedItems.addAll(it.position(currentMainAxis, layoutWidth, layoutHeight)) |
| currentMainAxis += it.sizeWithSpacings |
| } |
| } |
| return positionedItems |
| } |
