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LibWeb: Prune old paintable pointers from layout tree after relayout

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When text paintables shift around in the tree due to line wrapping,
we may end up in a situation where some text node does not generate
a paintable (due to being all whitespace, for example), even though
in the previous layout pass, it *did* generate a paintable.

To prevent holding on to old paintables in such cases, we now do a
pass in LayoutState::commit() where we explicitly detach all old
paintables from the layout tree.
This commit is contained in:
Andreas Kling 2023-08-29 16:27:16 +02:00
parent 390da2985f
commit 6d7a2f5cc9
3 changed files with 48 additions and 0 deletions
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27
Tests/LibWeb/Layout/expected/dont-crash-on-relayout-that-rewraps-text.txt Normal file
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@ -0,0 +1,27 @@
Viewport <#document> at (0,0) content-size 800x600 children: not-inline
BlockContainer <html> at (1,1) content-size 798x56.9375 [BFC] children: not-inline
BlockContainer <body> at (10,10) content-size 200x38.9375 children: inline
line 0 width: 196.0625, height: 19.46875, bottom: 19.46875, baseline: 14.53125
frag 0 from BlockContainer start: 0, length: 0, rect: [11,11 194.0625x17.46875]
line 1 width: 138.265625, height: 19.46875, bottom: 38.9375, baseline: 14.53125
frag 0 from BlockContainer start: 0, length: 0, rect: [11,30 136.265625x17.46875]
BlockContainer <div> at (11,11) content-size 194.0625x17.46875 inline-block [BFC] children: inline
line 0 width: 194.0625, height: 17.46875, bottom: 17.46875, baseline: 13.53125
frag 0 from TextNode start: 0, length: 20, rect: [11,11 194.0625x17.46875]
"xxxxxxxxxxxxxxxxxxxx"
TextNode <#text>
TextNode <#text>
BlockContainer <div> at (11,30) content-size 136.265625x17.46875 inline-block [BFC] children: inline
line 0 width: 136.265625, height: 17.46875, bottom: 17.46875, baseline: 13.53125
frag 0 from TextNode start: 0, length: 19, rect: [11,30 136.265625x17.46875]
"yyyyyyyyyyyyyyyyyyy"
TextNode <#text>
TextNode <#text>
ViewportPaintable (Viewport<#document>) [0,0 800x600]
PaintableWithLines (BlockContainer<HTML>) [0,0 800x58.9375]
PaintableWithLines (BlockContainer<BODY>) [9,9 202x40.9375]
PaintableWithLines (BlockContainer<DIV>) [10,10 196.0625x19.46875]
TextPaintable (TextNode<#text>)
PaintableWithLines (BlockContainer<DIV>) [10,29 138.265625x19.46875]
TextPaintable (TextNode<#text>)

13
Tests/LibWeb/Layout/input/dont-crash-on-relayout-that-rewraps-text.html Normal file
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@ -0,0 +1,13 @@
<!doctype html><style>
* {
border: 1px solid black;
}
div { display: inline-block; }
</style><body><div>xxxxxxxxxxxxxxxxxxxx</div> <div>yyyyyyyyyyyyyyyyyyy</div>
<script>
document.body.offsetWidth
document.body.style.width = "500px";
document.body.offsetWidth
document.body.style.width = "200px";
document.body.offsetWidth
</script>

8
Userland/Libraries/LibWeb/Layout/LayoutState.cpp
View file

@ -218,6 +218,14 @@ void LayoutState::commit(Box& root)
// Only the top-level LayoutState should ever be committed.
VERIFY(!m_parent);
// NOTE: In case this is a relayout of an existing tree, we start by detaching the old paint tree
// from the layout tree. This is done to ensure that we don't end up with any old-tree pointers
// when text paintables shift around in the tree.
root.for_each_in_inclusive_subtree_of_type<Layout::TextNode>([&](Layout::TextNode& text_node) {
text_node.set_paintable(nullptr);
return IterationDecision::Continue;
});
HashTable<Layout::TextNode*> text_nodes;
Vector<Painting::PaintableWithLines&> paintables_with_lines;