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LibWeb: Make SC hit testing more closely follow reverse paint order

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Previously, we would hit test positioned elements, then stacking
contexts with z-index 0, as two seperate steps. This did not really
follow the reverse paint order, where positioned elements and stacking
contexts with z-index 0 are painted during the same tree transversal.

This commit updates
for_each_in_subtree_of_type_within_same_stacking_context_in_reverse()
to return the stacking contexts it comes across too, but not recurse
into them. This more closely follows the paint order.

This fixes examples such as:

<div id="a" style="width: 10px; height: 10px">
  <div id="b" style="position: absolute; width: 10px; height: 10px">
    <div
     style="position: absolute; width: 10px; height: 10px; z-index: 0"
    >
      <div id="c"
           style="width: 100%; height: 100%; background-color:red;"
           onclick="alert('You Win!')">
      </div>
    </div>
  </div>
</div>

Where previously the onclick on #c would never fire as hit testing
always stopped at #b. This is reduced from Google Street View,
which becomes interactable after this commit.
This commit is contained in:
MacDue 2023-04-09 11:21:00 +01:00 • committed by Andreas Kling
parent 8fa9ca8b7f
commit d2fc8efd9e
1 changed files with 18 additions and 24 deletions
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42
Userland/Libraries/LibWeb/Painting/StackingContext.cpp
View file

@ -436,9 +436,12 @@ Gfx::FloatPoint StackingContext::compute_transform_origin() const
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())
if (is<PaintableBox>(paintable) && static_cast<PaintableBox const&>(paintable).stacking_context()) {
// Note: Include the stacking context (so we can hit test it), but don't recurse into it.
if (auto decision = callback(static_cast<U const&>(paintable)); decision != TraversalDecision::Continue)
return decision;
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;
@ -493,9 +496,8 @@ Optional<HitTestResult> StackingContext::hit_test(CSSPixelPoint position, HitTes
return result;
}
Optional<HitTestResult> result;
// 6. the child stacking contexts with stack level 0 and the positioned descendants with stack level 0.
Optional<HitTestResult> result;
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) {
@ -503,9 +505,18 @@ Optional<HitTestResult> StackingContext::hit_test(CSSPixelPoint position, HitTes
return TraversalDecision::SkipChildrenAndContinue;
}
auto const& z_index = paint_box.computed_values().z_index();
auto& layout_box = paint_box.layout_box();
if (z_index.value_or(0) == 0 && layout_box.is_positioned() && !paint_box.stacking_context()) {
auto candidate = paint_box.hit_test(transformed_position, type);
if (candidate.has_value() && candidate->paintable->visible_for_hit_testing()) {
result = move(candidate);
return TraversalDecision::Break;
}
}
if (paint_box.stacking_context()) {
auto const& z_index = paint_box.computed_values().z_index();
if (!z_index.has_value() || z_index.value() == 0) {
if (z_index.value_or(0) == 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);
@ -514,28 +525,11 @@ Optional<HitTestResult> StackingContext::hit_test(CSSPixelPoint position, HitTes
}
}
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()) {
result = move(candidate);
return TraversalDecision::Break;
}
}
return TraversalDecision::Continue;
});
if (result.has_value() && result->paintable->visible_for_hit_testing())
if (result.has_value())
return result;
// "child stacking contexts with stack level 0" is first in the step, so last here to match reverse order.
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)
break;
auto result = child.hit_test(transformed_position, type);
if (result.has_value() && result->paintable->visible_for_hit_testing())
return result;
}
// 5. the in-flow, inline-level, non-positioned descendants, including inline tables and inline blocks.
if (m_box->children_are_inline() && is<Layout::BlockContainer>(*m_box)) {
auto result = paintable().hit_test(transformed_position, type);