[GFC] Move PlacedGridItem construction from ImplicitGrid to GridFormattingContext.

https://bugs.webkit.org/show_bug.cgi?id=299533
rdar://problem/161337846

Reviewed by Brent Fulgham.

Currently, PlacedGridItems are created via placedGridItems() on
ImplicitGrid by constructing them out of the set of UnplacedGridItems
which it has mapped to different areas in the grid.

This has worked well enough for now, but as we prepare to size the
grid items, we need to be able to store additional data on these objects
in order to accomplish this. In particular, we need to store and be able
to use the various sizing properties (width, min-width, max-width, etc.)
for each dimension (inline vs block). However, we do not have enough
information at the ImplicitGrid level in order to map these properties
to the appropriate dimension. Instead, we should have GridFormattingContext
start creating these objects.

Not only will this allow us to correctly create PlacedGridItems with the
data that we need, but it also allows ImplicitGrid to return some simple
structures that describe the ImplicitGrid rather than a more complex
object.

* Source/WebCore/layout/formattingContexts/grid/GridLayout.cpp:
(WebCore::Layout::GridLayout::placeGridItems):
(WebCore::Layout::GridLayout::layout):
Previously we were getting the PlacedGridItems as a result of the grid
item placement portion (placeGridItems()) of the layout algorithm. Now
we get the grid areas for each item which were resolved from that
process. We can then ask the GridFormattingContext to create the set of
PlacedGridItems from this data.

* Source/WebCore/layout/formattingContexts/grid/ImplicitGrid.cpp:
(WebCore::Layout::ImplicitGrid::gridAreas const):
Instead of returning PlacedGridItems we return the set of grid areas
contained within the ImplicitGrid. This is just a map of each item that
has been placed in the grid along with the area (set of lines) that it
has been placed in. The caller can then take the UnplacedGridItem and
its grid area and do whatever it needs to which includes constructing a
PlacedGridItem if they need it.

Canonical link: https://commits.webkit.org/300547@main

Author: sammygill

Source/WebCore/WebCore.xcodeproj/project.pbxproj

@@ -4344,6 +4344,7 @@
 		A5DEBDA416FB908700836FE0 /* WebKitPlaybackTargetAvailabilityEvent.h in Headers */ = {isa = PBXBuildFile; fileRef = A5DEBDA016FB908700836FE0 /* WebKitPlaybackTargetAvailabilityEvent.h */; };
 		A5F36D3B18F758720054C024 /* PageDebugger.h in Headers */ = {isa = PBXBuildFile; fileRef = A5F36D3918F758720054C024 /* PageDebugger.h */; settings = {ATTRIBUTES = (Private, ); }; };
 		A5FA575E2E85BFE500EF058F /* LayoutIntegrationGridCoverage.h in Headers */ = {isa = PBXBuildFile; fileRef = A5FA575C2E85BFDE00EF058F /* LayoutIntegrationGridCoverage.h */; settings = {ATTRIBUTES = (Private, ); }; };
+		A5FA57662E85F40D00EF058F /* GridAreaLines.h in Headers */ = {isa = PBXBuildFile; fileRef = A5FA57652E85F40600EF058F /* GridAreaLines.h */; settings = {ATTRIBUTES = (Private, ); }; };
 		A6D169641346B4C1000EB770 /* ShadowRoot.h in Headers */ = {isa = PBXBuildFile; fileRef = A6D169631346B4C1000EB770 /* ShadowRoot.h */; settings = {ATTRIBUTES = (Private, ); }; };
 		A6D5A99D1629D70000297330 /* ScrollingTreeScrollingNodeDelegate.h in Headers */ = {isa = PBXBuildFile; fileRef = A6D5A99B1629D70000297330 /* ScrollingTreeScrollingNodeDelegate.h */; settings = {ATTRIBUTES = (Private, ); }; };
 		A70B77D62A9EE40B003D8566 /* Quaternion.h in Headers */ = {isa = PBXBuildFile; fileRef = A70B77D52A9EE40B003D8566 /* Quaternion.h */; settings = {ATTRIBUTES = (Private, ); }; };
@@ -16883,6 +16884,7 @@
 		A5F6E16C132ED46E008EDAE3 /* Autocapitalize.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = Autocapitalize.cpp; sourceTree = "<group>"; };
 		A5FA575C2E85BFDE00EF058F /* LayoutIntegrationGridCoverage.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = LayoutIntegrationGridCoverage.h; sourceTree = "<group>"; };
 		A5FA575D2E85BFDE00EF058F /* LayoutIntegrationGridCoverage.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = LayoutIntegrationGridCoverage.cpp; sourceTree = "<group>"; };
+		A5FA57652E85F40600EF058F /* GridAreaLines.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = GridAreaLines.h; sourceTree = "<group>"; };
 		A5FD1D922ADDF9CC00F90FE5 /* AncestorSubgridIterator.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = AncestorSubgridIterator.cpp; sourceTree = "<group>"; };
 		A5FD1D932ADDF9CC00F90FE5 /* AncestorSubgridIterator.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = AncestorSubgridIterator.h; sourceTree = "<group>"; };
 		A6D169611346B49B000EB770 /* ShadowRoot.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = ShadowRoot.cpp; sourceTree = "<group>"; };
@@ -32520,6 +32522,7 @@
 		A585CC412E566A7800A69390 /* grid */ = {
 			isa = PBXGroup;
 			children = (
+				A5FA57652E85F40600EF058F /* GridAreaLines.h */,
 				A585CC3E2E566A7800A69390 /* GridFormattingContext.cpp */,
 				A585CC3D2E566A7800A69390 /* GridFormattingContext.h */,
 				A585CC402E566A7800A69390 /* GridLayout.cpp */,
@@ -42959,6 +42962,7 @@
 				77A17A7B12F2890B004E02F6 /* GraphicsTypesGL.h in Headers */,
 				E112F4721E3A861600D6CDFD /* Grid.h in Headers */,
 				CD3E251C18046B0600E27F56 /* GridArea.h in Headers */,
+				A5FA57662E85F40D00EF058F /* GridAreaLines.h in Headers */,
 				A585CC442E566A7800A69390 /* GridFormattingContext.h in Headers */,
 				A585CC452E566A7800A69390 /* GridLayout.h in Headers */,
 				A54CAA142C409C4500D6A999 /* GridLayoutState.h in Headers */,

Source/WebCore/layout/formattingContexts/grid/GridAreaLines.h

@@ -0,0 +1,38 @@
+/*
+ * 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.
+ */
+
+#pragma once
+
+namespace WebCore {
+namespace Layout {
+// https://drafts.csswg.org/css-grid-1/#grid-area
+struct GridAreaLines {
+    size_t columnStartLine;
+    size_t columnEndLine;
+    size_t rowStartLine;
+    size_t rowEndLine;
+};
+}
+}

Source/WebCore/layout/formattingContexts/grid/GridFormattingContext.cpp

@@ -28,6 +28,7 @@
 
 #include "GridLayout.h"
 #include "LayoutChildIterator.h"
+#include "PlacedGridItem.h"
 #include "RenderStyleInlines.h"
 #include "StylePrimitiveNumeric.h"
 #include "UnplacedGridItem.h"
@@ -112,5 +113,15 @@ void GridFormattingContext::layout(GridLayoutConstraints layoutConstraints)
     GridLayout { *this }.layout(layoutConstraints, unplacedGridItems);
 }
 
+GridFormattingContext::PlacedGridItems GridFormattingContext::constructPlacedGridItems(const GridAreas& gridAreas) const
+{
+    PlacedGridItems placedGridItems;
+    placedGridItems.reserveInitialCapacity(gridAreas.size());
+    for (auto [ unplacedGridItem, gridAreaLines ] : gridAreas)
+        placedGridItems.constructAndAppend(unplacedGridItem, gridAreaLines);
+
+    return placedGridItems;
+}
+
 } // namespace Layout
 } // namespace WebCore

Source/WebCore/layout/formattingContexts/grid/GridFormattingContext.h

@@ -33,8 +33,11 @@ namespace WebCore {
 namespace Layout {
 
 class ElementBox;
+class PlacedGridItem;
 
 class UnplacedGridItem;
+
+struct GridAreaLines;
 struct UnplacedGridItems;
 
 class GridFormattingContext : public CanMakeCheckedPtr<GridFormattingContext> {
@@ -51,6 +54,10 @@ class GridFormattingContext : public CanMakeCheckedPtr<GridFormattingContext> {
 
     void layout(GridLayoutConstraints);
 
+    using PlacedGridItems = Vector<PlacedGridItem>;
+    using GridAreas = HashMap<UnplacedGridItem, GridAreaLines>;
+    PlacedGridItems constructPlacedGridItems(const GridAreas&) const;
+
     const ElementBox& root() const { return m_gridBox; }
 
 private:

Source/WebCore/layout/formattingContexts/grid/GridLayout.cpp

@@ -48,7 +48,8 @@ auto GridLayout::placeGridItems(const UnplacedGridItems& unplacedGridItems, cons
     const Vector<Style::GridTrackSize>& gridTemplateRowsTrackSizes)
 {
     struct Result {
-        PlacedGridItems placedGridItems;
+        using GridAreas = HashMap<UnplacedGridItem, GridAreaLines>;
+        GridAreas gridAreas;
         size_t implicitGridColumnsCount;
         size_t implicitGridRowsCount;
     };
@@ -63,7 +64,7 @@ auto GridLayout::placeGridItems(const UnplacedGridItems& unplacedGridItems, cons
     ASSERT(implicitGrid.columnsCount() == gridTemplateColumnsTrackSizes.size() && implicitGrid.rowsCount() == gridTemplateRowsTrackSizes.size(),
         "Since we currently only support placing items which are explicitly placed and fit within the explicit grid, the size of the implicit grid should match the passed in sizes.");
 
-    return Result { implicitGrid.placedGridItems(), implicitGrid.columnsCount(), implicitGrid.rowsCount() };
+    return Result { implicitGrid.gridAreas(), implicitGrid.columnsCount(), implicitGrid.rowsCount() };
 }
 
 // https://drafts.csswg.org/css-grid-1/#layout-algorithm
@@ -74,7 +75,8 @@ void GridLayout::layout(GridFormattingContext::GridLayoutConstraints, const Unpl
     auto& gridTemplateRowsTrackSizes = gridContainerStyle->gridTemplateRows().sizes;
 
     // 1. Run the Grid Item Placement Algorithm to resolve the placement of all grid items in the grid.
-    auto [ placedGridItems, implicitGridColumnsCount, implicitGridRowsCount ] = placeGridItems(unplacedGridItems, gridTemplateColumnsTrackSizes, gridTemplateRowsTrackSizes);
+    auto [ gridAreas, implicitGridColumnsCount, implicitGridRowsCount ] = placeGridItems(unplacedGridItems, gridTemplateColumnsTrackSizes, gridTemplateRowsTrackSizes);
+    auto placedGridItems = formattingContext().constructPlacedGridItems(gridAreas);
 
     auto columnTrackSizingFunctionsList = trackSizingFunctions(implicitGridColumnsCount, gridTemplateColumnsTrackSizes);
     auto rowTrackSizingFunctionsList = trackSizingFunctions(implicitGridRowsCount, gridTemplateRowsTrackSizes);

Source/WebCore/layout/formattingContexts/grid/GridLayout.h

@@ -68,6 +68,8 @@ class GridLayout {
     };
     static UsedTrackSizes performGridSizingAlgorithm(const PlacedGridItems&, const TrackSizingFunctionsList& columnTrackSizingFunctionsList, const TrackSizingFunctionsList& rowTrackSizingFunctionsList);
 
+    const GridFormattingContext& formattingContext() const { return m_gridFormattingContext.get(); }
+
     const ElementBox& gridContainer() const;
     const RenderStyle& gridContainerStyle() const;
 

Source/WebCore/layout/formattingContexts/grid/ImplicitGrid.cpp

@@ -100,24 +100,23 @@ void ImplicitGrid::insertUnplacedGridItem(const UnplacedGridItem& unplacedGridIt
 
 }
 
-PlacedGridItems ImplicitGrid::placedGridItems() const
+ImplicitGrid::GridAreas ImplicitGrid::gridAreas() const
 {
-    HashSet<UnplacedGridItem> processedUnplacedGridItems;
-    PlacedGridItems placedGridItems;
+    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) {
-                if (processedUnplacedGridItems.contains(unplacedGridItem))
-                    continue;
-                processedUnplacedGridItems.add(unplacedGridItem);
-                placedGridItems.append({ unplacedGridItem, { columnIndex, columnIndex + 1, rowIndex, rowIndex + 1 } });
+                gridAreas.ensure(unplacedGridItem, [&]() {
+                    return GridAreaLines { columnIndex, columnIndex + 1, rowIndex, rowIndex + 1 };
+                });
             }
         }
     }
-    return placedGridItems;
+    return gridAreas;
 }
 
 } // namespace Layout

Source/WebCore/layout/formattingContexts/grid/ImplicitGrid.h

@@ -34,6 +34,8 @@ namespace Layout {
 class PlacedGridItem;
 class UnplacedGridItem;
 
+struct GridAreaLines;
+
 using PlacedGridItems = Vector<PlacedGridItem>;
 using GridCell = Vector<UnplacedGridItem, 1>;
 
@@ -47,7 +49,8 @@ class ImplicitGrid {
 
     void insertUnplacedGridItem(const UnplacedGridItem&);
 
-    PlacedGridItems placedGridItems() const;
+    using GridAreas = HashMap<UnplacedGridItem, GridAreaLines>;
+    GridAreas gridAreas() const;
 
 private:
     using GridMatrix = Vector<Vector<GridCell>>;

Source/WebCore/layout/formattingContexts/grid/PlacedGridItem.h

@@ -25,6 +25,7 @@
 
 #pragma once
 
+#include "GridAreaLines.h"
 #include "LayoutElementBox.h"
 #include <wtf/HashTraits.h>
 
@@ -35,13 +36,6 @@ class UnplacedGridItem;
 
 class PlacedGridItem {
 public:
-    // https://drafts.csswg.org/css-grid-1/#grid-area
-    struct GridAreaLines {
-        size_t columnStartLine;
-        size_t columnEndLine;
-        size_t rowStartLine;
-        size_t rowEndLine;
-    };
 
     PlacedGridItem(const UnplacedGridItem&, GridAreaLines);
 

Source/WebCore/layout/formattingContexts/grid/UnplacedGridItem.h

@@ -84,6 +84,7 @@ template<> struct HashTraits<WebCore::Layout::UnplacedGridItem> : SimpleClassHas
     static constexpr bool hasIsEmptyValueFunction = true;
 
     static bool isEmptyValue(const WebCore::Layout::UnplacedGridItem& unplacedGridItem) { return unplacedGridItem.isHashTableEmptyValue(); }
+    static WebCore::Layout::UnplacedGridItem emptyValue() { return WebCore::Layout::UnplacedGridItem { HashTableEmptyValueType::HashTableEmptyValue }; }
 };
 
 template<> struct DefaultHash<WebCore::Layout::UnplacedGridItem> {