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LibWeb: Make hit testing traverse positioned descendants in right order

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We were doing a forward traversal in hit testing which led to sometimes
incorrect results when multiple boxes were occupying the same X and Y
coordinate.
This commit is contained in:
Andreas Kling 2022-11-03 19:08:07 +01:00
parent f2ccb702e8
commit 5aeb6fec68
Notes: sideshowbarker 2024-07-17 04:48:01 +09:00 
Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/5aeb6fec68
3 changed files with 71 additions and 8 deletions
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16
Userland/Libraries/LibWeb/Painting/Paintable.cpp
View file

@ -62,4 +62,20 @@ Paintable const* Paintable::next_sibling() const
return layout_node ? layout_node->paintable() : nullptr;
}
Paintable const* Paintable::last_child() const
{
auto* layout_child = m_layout_node.last_child();
for (; layout_child && !layout_child->paintable(); layout_child = layout_child->previous_sibling())
;
return layout_child ? layout_child->paintable() : nullptr;
}
Paintable const* Paintable::previous_sibling() const
{
auto* layout_node = m_layout_node.previous_sibling();
for (; layout_node && !layout_node->paintable(); layout_node = layout_node->previous_sibling())
;
return layout_node ? layout_node->paintable() : nullptr;
}
}

4
Userland/Libraries/LibWeb/Painting/Paintable.h
View file

@ -56,13 +56,15 @@ public:
virtual ~Paintable() = default;
Paintable const* first_child() const;
Paintable const* last_child() const;
Paintable const* next_sibling() const;
Paintable const* previous_sibling() const;
template<typename U, typename Callback>
TraversalDecision for_each_in_inclusive_subtree_of_type(Callback callback) const
{
if (is<U>(*this)) {
if (auto decision = callback(static_cast<const U&>(*this)); decision != TraversalDecision::Continue)
if (auto decision = callback(static_cast<U const&>(*this)); decision != TraversalDecision::Continue)
return decision;
}
for (auto* child = first_child(); child; child = child->next_sibling()) {

59
Userland/Libraries/LibWeb/Painting/StackingContext.cpp
View file

@ -407,6 +407,33 @@ Gfx::FloatPoint StackingContext::compute_transform_origin() const
return { x, y };
}
template<typename U, typename Callback>
static TraversalDecision for_each_in_inclusive_subtree_of_type_within_same_stacking_context_in_reverse(Paintable const& paintable, Callback callback)
{
if (is<PaintableBox>(paintable) && static_cast<PaintableBox const&>(paintable).stacking_context())
return TraversalDecision::SkipChildrenAndContinue;
for (auto* child = paintable.last_child(); child; child = child->previous_sibling()) {
if (for_each_in_inclusive_subtree_of_type_within_same_stacking_context_in_reverse<U>(*child, callback) == TraversalDecision::Break)
return TraversalDecision::Break;
}
if (is<U>(paintable)) {
if (auto decision = callback(static_cast<U const&>(paintable)); decision != TraversalDecision::Continue)
return decision;
}
return TraversalDecision::Continue;
}
template<typename U, typename Callback>
static TraversalDecision for_each_in_subtree_of_type_within_same_stacking_context_in_reverse(Paintable const& paintable, Callback callback)
{
for (auto* child = paintable.last_child(); child; child = child->previous_sibling()) {
if (for_each_in_inclusive_subtree_of_type_within_same_stacking_context_in_reverse<U>(*child, callback) == TraversalDecision::Break)
return TraversalDecision::Break;
}
return TraversalDecision::Continue;
}
Optional<HitTestResult> StackingContext::hit_test(Gfx::FloatPoint const& position, HitTestType type) const
{
if (!m_box.is_visible())
@ -428,7 +455,7 @@ Optional<HitTestResult> StackingContext::hit_test(Gfx::FloatPoint const& positio
// NOTE: Hit testing follows reverse painting order, that's why the conditions here are reversed.
for (ssize_t i = m_children.size() - 1; i >= 0; --i) {
auto const& child = *m_children[i];
if (child.m_box.computed_values().z_index().value_or(0) < 0)
if (child.m_box.computed_values().z_index().value_or(0) <= 0)
break;
auto result = child.hit_test(transformed_position, type);
if (result.has_value() && result->paintable->visible_for_hit_testing())
@ -437,17 +464,31 @@ Optional<HitTestResult> StackingContext::hit_test(Gfx::FloatPoint const& positio
Optional<HitTestResult> result;
// 6. the child stacking contexts with stack level 0 and the positioned descendants with stack level 0.
paintable().for_each_in_subtree_of_type<PaintableBox>([&](auto& paint_box) {
for_each_in_subtree_of_type_within_same_stacking_context_in_reverse<PaintableBox>(paintable(), [&](PaintableBox const& paint_box) {
// FIXME: Support more overflow variations.
if (paint_box.computed_values().overflow_x() == CSS::Overflow::Hidden && paint_box.computed_values().overflow_y() == CSS::Overflow::Hidden) {
if (!paint_box.absolute_border_box_rect().contains(transformed_position.x(), transformed_position.y()))
return TraversalDecision::SkipChildrenAndContinue;
}
if (paint_box.stacking_context()) {
auto const& z_index = paint_box.computed_values().z_index();
if (!z_index.has_value() || z_index.value() == 0) {
auto candidate = paint_box.stacking_context()->hit_test(transformed_position, type);
if (candidate.has_value() && candidate->paintable->visible_for_hit_testing()) {
result = move(candidate);
return TraversalDecision::Break;
}
}
}
auto& layout_box = paint_box.layout_box();
if (layout_box.is_positioned() && !paint_box.stacking_context()) {
if (auto candidate = paint_box.hit_test(transformed_position, type); candidate.has_value())
if (auto candidate = paint_box.hit_test(transformed_position, type); candidate.has_value()) {
result = move(candidate);
return TraversalDecision::Break;
}
}
return TraversalDecision::Continue;
});
@ -462,7 +503,7 @@ Optional<HitTestResult> StackingContext::hit_test(Gfx::FloatPoint const& positio
}
// 4. the non-positioned floats.
paintable().for_each_in_subtree_of_type<PaintableBox>([&](auto const& paint_box) {
for_each_in_subtree_of_type_within_same_stacking_context_in_reverse<PaintableBox>(paintable(), [&](auto const& paint_box) {
// FIXME: Support more overflow variations.
if (paint_box.computed_values().overflow_x() == CSS::Overflow::Hidden && paint_box.computed_values().overflow_y() == CSS::Overflow::Hidden) {
if (!paint_box.absolute_border_box_rect().contains(transformed_position.x(), transformed_position.y()))
@ -471,8 +512,10 @@ Optional<HitTestResult> StackingContext::hit_test(Gfx::FloatPoint const& positio
auto& layout_box = paint_box.layout_box();
if (layout_box.is_floating()) {
if (auto candidate = paint_box.hit_test(transformed_position, type); candidate.has_value())
if (auto candidate = paint_box.hit_test(transformed_position, type); candidate.has_value()) {
result = move(candidate);
return TraversalDecision::Break;
}
}
return TraversalDecision::Continue;
});
@ -481,7 +524,7 @@ Optional<HitTestResult> StackingContext::hit_test(Gfx::FloatPoint const& positio
// 3. the in-flow, non-inline-level, non-positioned descendants.
if (!m_box.children_are_inline()) {
paintable().for_each_in_subtree_of_type<PaintableBox>([&](auto const& paint_box) {
for_each_in_subtree_of_type_within_same_stacking_context_in_reverse<PaintableBox>(paintable(), [&](auto const& paint_box) {
// FIXME: Support more overflow variations.
if (paint_box.computed_values().overflow_x() == CSS::Overflow::Hidden && paint_box.computed_values().overflow_y() == CSS::Overflow::Hidden) {
if (!paint_box.absolute_border_box_rect().contains(transformed_position.x(), transformed_position.y()))
@ -490,8 +533,10 @@ Optional<HitTestResult> StackingContext::hit_test(Gfx::FloatPoint const& positio
auto& layout_box = paint_box.layout_box();
if (!layout_box.is_absolutely_positioned() && !layout_box.is_floating()) {
if (auto candidate = paint_box.hit_test(transformed_position, type); candidate.has_value())
if (auto candidate = paint_box.hit_test(transformed_position, type); candidate.has_value()) {
result = move(candidate);
return TraversalDecision::Break;
}
}
return TraversalDecision::Continue;
});