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/*
* Copyright (C) 2025 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
* THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "config.h"
#include "ImplicitGrid.h"
#include "GridAreaLines.h"
#include "GridLayout.h"
#include "PlacedGridItem.h"
#include "UnplacedGridItem.h"
#include <wtf/Assertions.h>
#include <wtf/Range.h>
namespace WebCore {
namespace Layout {
// The implicit grid is created from the explicit grid + items that are placed outside
// of the explicit grid. Since we know the explicit tracks from style we start the
// implicit grid as exactly the explicit grid and allow placement to add implicit
// tracks and grow the grid.
ImplicitGrid::ImplicitGrid(size_t totalColumnsCount, size_t totalRowsCount)
: m_gridMatrix(Vector(totalRowsCount, Vector<GridCell>(totalColumnsCount)))
{
}
void ImplicitGrid::insertUnplacedGridItem(const UnplacedGridItem& unplacedGridItem)
{
// https://drafts.csswg.org/css-grid/#common-uses-numeric
// Grid positions have already been normalized to non-negative matrix indices.
auto [columnStart, columnEnd] = unplacedGridItem.normalizedColumnStartEnd();
auto [rowStart, rowEnd] = unplacedGridItem.normalizedRowStartEnd();
// Multi-cell items (spanning multiple columns) are not yet supported.
if (columnEnd - columnStart > 1) {
ASSERT_NOT_IMPLEMENTED_YET();
return;
}
// Multi-cell items (spanning multiple rows) are not yet supported.
if (rowEnd - rowStart > 1) {
ASSERT_NOT_IMPLEMENTED_YET();
return;
}
auto columnsRange = WTF::Range(columnStart, columnEnd);
auto rowsRange = WTF::Range(rowStart, rowEnd);
for (auto rowIndex = rowsRange.begin(); rowIndex < rowsRange.end(); ++rowIndex) {
for (auto columnIndex = columnsRange.begin(); columnIndex < columnsRange.end(); ++columnIndex)
m_gridMatrix[rowIndex][columnIndex].append(unplacedGridItem);
}
}
GridAreas ImplicitGrid::gridAreas() const
{
GridAreas gridAreas;
gridAreas.reserveInitialCapacity(rowsCount() * columnsCount());
for (size_t rowIndex = 0; rowIndex < m_gridMatrix.size(); ++rowIndex) {
for (size_t columnIndex = 0; columnIndex < m_gridMatrix[rowIndex].size(); ++columnIndex) {
const auto& gridCell = m_gridMatrix[rowIndex][columnIndex];
for (const auto& unplacedGridItem : gridCell) {
gridAreas.ensure(unplacedGridItem, [&]() {
return GridAreaLines { columnIndex, columnIndex + 1, rowIndex, rowIndex + 1 };
});
}
}
}
return gridAreas;
}
void ImplicitGrid::insertDefiniteRowItem(const UnplacedGridItem& unplacedGridItem, GridAutoFlowOptions autoFlowOptions, HashMap<size_t, size_t, DefaultHash<size_t>, WTF::UnsignedWithZeroKeyHashTraits<size_t>>* rowCursors)
{
// Step 2 of CSS Grid auto-placement algorithm:
// Process items locked to a given row (definite row position, auto column position)
// See: https://www.w3.org/TR/css-grid-1/#auto-placement-algo
auto columnSpan = unplacedGridItem.columnSpanSize();
// FIXME: Support multi-column spans
ASSERT(columnSpan == 1);
ASSERT(unplacedGridItem.hasDefiniteRowPosition() && !unplacedGridItem.hasDefiniteColumnPosition());
auto [normalizedRowStart, normalizedRowEnd] = unplacedGridItem.normalizedRowStartEnd();
// FIXME: Support multi-row spans
ASSERT(normalizedRowEnd - normalizedRowStart == 1);
auto findColumnPosition = [&]() -> std::optional<size_t> {
if (autoFlowOptions.strategy == PackingStrategy::Dense) {
// Dense packing: always start searching from column 0
return findFirstAvailableColumnPosition(normalizedRowStart, normalizedRowEnd, columnSpan, 0);
}
// Sparse packing: use per-row cursors to maintain placement order
// For multi-row items, use the maximum cursor position across all spanned rows
ASSERT(autoFlowOptions.strategy == PackingStrategy::Sparse);
size_t startSearchColumn = 0;
for (size_t row = normalizedRowStart; row < normalizedRowEnd; ++row)
startSearchColumn = std::max(startSearchColumn, rowCursors->get(row));
return findFirstAvailableColumnPosition(normalizedRowStart, normalizedRowEnd, columnSpan, startSearchColumn);
};
auto growGridToFit = [&](size_t columnSpan, size_t normalizedRowStart, size_t normalizedRowEnd, size_t currentColumnsCount) {
// Find the last occupied column in the spanned rows
size_t lastOccupiedColumn = 0;
for (size_t row = normalizedRowStart; row < normalizedRowEnd; ++row) {
for (size_t column = currentColumnsCount; column > 0; --column) {
if (!m_gridMatrix[row][column - 1].isEmpty()) {
lastOccupiedColumn = std::max(lastOccupiedColumn, column - 1);
break;
}
}
}
size_t minimumColumnsNeeded = lastOccupiedColumn + 1 + columnSpan;
for (auto& row : m_gridMatrix)
row.resize(minimumColumnsNeeded);
};
auto columnPosition = findColumnPosition();
if (!columnPosition) {
growGridToFit(columnSpan, normalizedRowStart, normalizedRowEnd, columnsCount());
// Retry finding position in the grown grid
columnPosition = findColumnPosition();
#ifndef NDEBUG
ASSERT(columnPosition); // Must succeed after growing
// Verify the found position doesn't overlap with existing items
ASSERT(isCellRangeEmpty(*columnPosition, *columnPosition + columnSpan, normalizedRowStart, normalizedRowEnd),
"After grid growth, placed item overlaps with occupied cells.");
auto verifyHasEmptyLastColumn = [&]() {
for (size_t row = 0; row < m_gridMatrix.size(); ++row) {
if (!m_gridMatrix[row].last().isEmpty())
return false;
}
ASSERT_NOT_REACHED();
return true;
};
verifyHasEmptyLastColumn();
#endif
}
insertItemInArea(unplacedGridItem, *columnPosition, *columnPosition + columnSpan, normalizedRowStart, normalizedRowEnd);
if (autoFlowOptions.strategy != PackingStrategy::Dense) {
for (size_t row = normalizedRowStart; row < normalizedRowEnd; ++row)
rowCursors->set(row, *columnPosition + columnSpan);
}
}
std::optional<size_t> ImplicitGrid::findFirstAvailableColumnPosition(size_t rowStart, size_t rowEnd, size_t columnSpan, size_t startSearchColumn) const
{
auto currentColumnsCount = columnsCount();
// If we can't fit the span starting from the search position, signal that we need to grow the grid
if (startSearchColumn + columnSpan > currentColumnsCount)
return std::nullopt;
// Search within existing grid bounds
for (size_t columnStart = startSearchColumn; columnStart <= currentColumnsCount - columnSpan; ++columnStart) {
if (isCellRangeEmpty(columnStart, columnStart + columnSpan, rowStart, rowEnd))
return columnStart;
}
// If we are unable to find a valid position, signal that we need to grow the grid.
return std::nullopt;
}
bool ImplicitGrid::isCellRangeEmpty(size_t columnStart, size_t columnEnd, size_t rowStart, size_t rowEnd) const
{
for (size_t row = rowStart; row < rowEnd; ++row) {
for (size_t column = columnStart; column < columnEnd; ++column) {
if (!m_gridMatrix[row][column].isEmpty())
return false;
}
}
return true;
}
void ImplicitGrid::insertItemInArea(const UnplacedGridItem& unplacedGridItem, size_t columnStart, size_t columnEnd, size_t rowStart, size_t rowEnd)
{
for (size_t row = rowStart; row < rowEnd; ++row) {
for (size_t column = columnStart; column < columnEnd; ++column)
m_gridMatrix[row][column].append(unplacedGridItem);
}
}
} // namespace Layout
} // namespace WebCore
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