LibWeb: Make StackingContext point to paint tree instead of layout tree

Eventually we should not need the layout tree for anything when painting
and this code will only look at the paint tree. For now, this is just
another step in that direction.
This commit is contained in:
Andreas Kling 2023-08-19 15:20:45 +02:00
parent 1e0ea45fe5
commit d296992fb3
6 changed files with 86 additions and 100 deletions

View file

@ -56,6 +56,13 @@ class Paintable
public:
virtual ~Paintable() = default;
[[nodiscard]] bool is_positioned() const { return layout_node().is_positioned(); }
[[nodiscard]] bool is_fixed_position() const { return layout_node().is_fixed_position(); }
[[nodiscard]] bool is_absolutely_positioned() const { return layout_node().is_absolutely_positioned(); }
[[nodiscard]] bool is_floating() const { return layout_node().is_floating(); }
[[nodiscard]] bool is_inline() const { return layout_node().is_inline(); }
[[nodiscard]] CSS::Display display() const { return layout_node().display(); }
template<typename U, typename Callback>
TraversalDecision for_each_in_inclusive_subtree_of_type(Callback callback) const
{

View file

@ -24,15 +24,14 @@
namespace Web::Painting {
static void paint_node(Layout::Node const& layout_node, PaintContext& context, PaintPhase phase)
static void paint_node(Paintable const& paintable, PaintContext& context, PaintPhase phase)
{
if (auto const* paintable = layout_node.paintable())
paintable->paint(context, phase);
paintable.paint(context, phase);
}
StackingContext::StackingContext(Layout::Box& box, StackingContext* parent, size_t index_in_tree_order)
: m_box(box)
, m_transform(combine_transformations(m_box->computed_values().transformations()))
StackingContext::StackingContext(PaintableBox& paintable_box, StackingContext* parent, size_t index_in_tree_order)
: m_paintable_box(paintable_box)
, m_transform(combine_transformations(paintable_box.computed_values().transformations()))
, m_transform_origin(compute_transform_origin())
, m_parent(parent)
, m_index_in_tree_order(index_in_tree_order)
@ -45,8 +44,8 @@ StackingContext::StackingContext(Layout::Box& box, StackingContext* parent, size
void StackingContext::sort()
{
quick_sort(m_children, [](auto& a, auto& b) {
auto a_z_index = a->m_box->computed_values().z_index().value_or(0);
auto b_z_index = b->m_box->computed_values().z_index().value_or(0);
auto a_z_index = a->paintable_box().computed_values().z_index().value_or(0);
auto b_z_index = b->paintable_box().computed_values().z_index().value_or(0);
if (a_z_index == b_z_index)
return a->m_index_in_tree_order < b->m_index_in_tree_order;
return a_z_index < b_z_index;
@ -73,23 +72,13 @@ static PaintPhase to_paint_phase(StackingContext::StackingContextPaintPhase phas
}
}
void StackingContext::paint_descendants(PaintContext& context, Layout::Node const& box, StackingContextPaintPhase phase) const
void StackingContext::paint_descendants(PaintContext& context, Paintable const& paintable, StackingContextPaintPhase phase) const
{
if (auto* paintable = box.paintable()) {
paintable->before_children_paint(context, to_paint_phase(phase));
paintable->apply_clip_overflow_rect(context, to_paint_phase(phase));
}
paintable.before_children_paint(context, to_paint_phase(phase));
paintable.apply_clip_overflow_rect(context, to_paint_phase(phase));
auto child_stacking_context = [&](auto& child) -> StackingContext const* {
if (auto* paintable = child.paintable()) {
if (auto* stacking_context = paintable->stacking_context_rooted_here())
return stacking_context;
}
return nullptr;
};
box.for_each_child([&](auto& child) {
auto* stacking_context = child_stacking_context(child);
paintable.for_each_child([this, &context, phase](auto& child) {
auto* stacking_context = child.stacking_context_rooted_here();
if (child.is_positioned()) {
// If `child` is positioned with a z-index of `0` or `auto`, skip over it.
@ -120,7 +109,7 @@ void StackingContext::paint_descendants(PaintContext& context, Layout::Node cons
paint_node(child, context, PaintPhase::Border);
paint_descendants(context, child, phase);
if (child.display().is_table_inside() || child.computed_values().border_collapse() == CSS::BorderCollapse::Collapse) {
paint_table_borders(context, child);
paint_table_borders(context, verify_cast<PaintableBox>(child));
}
}
break;
@ -137,7 +126,7 @@ void StackingContext::paint_descendants(PaintContext& context, Layout::Node cons
paint_node(child, context, PaintPhase::Background);
paint_node(child, context, PaintPhase::Border);
if (child.display().is_table_inside() && child.computed_values().border_collapse() == CSS::BorderCollapse::Separate)
paint_table_borders(context, child);
paint_table_borders(context, verify_cast<PaintableBox>(child));
paint_descendants(context, child, StackingContextPaintPhase::BackgroundAndBorders);
}
paint_descendants(context, child, phase);
@ -154,19 +143,16 @@ void StackingContext::paint_descendants(PaintContext& context, Layout::Node cons
}
});
if (auto* paintable = box.paintable()) {
paintable->clear_clip_overflow_rect(context, to_paint_phase(phase));
paintable->after_children_paint(context, to_paint_phase(phase));
}
paintable.clear_clip_overflow_rect(context, to_paint_phase(phase));
paintable.after_children_paint(context, to_paint_phase(phase));
}
void StackingContext::paint_child(PaintContext& context, StackingContext const& child) const
{
auto parent = child.m_box->parent();
auto* parent_paintable = parent ? parent->paintable() : nullptr;
auto parent_paintable = child.paintable_box().parent();
if (parent_paintable)
parent_paintable->before_children_paint(context, PaintPhase::Foreground);
auto containing_block = child.m_box->containing_block();
auto containing_block = child.paintable_box().containing_block();
auto* containing_block_paintable = containing_block ? containing_block->paintable() : nullptr;
if (containing_block_paintable)
containing_block_paintable->apply_clip_overflow_rect(context, PaintPhase::Foreground);
@ -183,34 +169,33 @@ void StackingContext::paint_internal(PaintContext& context) const
{
// For a more elaborate description of the algorithm, see CSS 2.1 Appendix E
// Draw the background and borders for the context root (steps 1, 2)
paint_node(m_box, context, PaintPhase::Background);
paint_node(m_box, context, PaintPhase::Border);
paint_node(paintable_box(), context, PaintPhase::Background);
paint_node(paintable_box(), context, PaintPhase::Border);
// Stacking contexts formed by positioned descendants with negative z-indices (excluding 0) in z-index order
// (most negative first) then tree order. (step 3)
for (auto* child : m_children) {
if (!child->paintable_box().layout_box().is_positioned())
if (!child->paintable_box().is_positioned())
continue;
if (child->paintable_box().computed_values().z_index().has_value() && child->m_box->computed_values().z_index().value() < 0)
if (child->paintable_box().computed_values().z_index().has_value() && child->paintable_box().computed_values().z_index().value() < 0)
paint_child(context, *child);
}
// Draw the background and borders for block-level children (step 4)
paint_descendants(context, m_box, StackingContextPaintPhase::BackgroundAndBorders);
paint_descendants(context, paintable_box(), StackingContextPaintPhase::BackgroundAndBorders);
// Draw the non-positioned floats (step 5)
paint_descendants(context, m_box, StackingContextPaintPhase::Floats);
paint_descendants(context, paintable_box(), StackingContextPaintPhase::Floats);
// Draw inline content, replaced content, etc. (steps 6, 7)
paint_descendants(context, m_box, StackingContextPaintPhase::BackgroundAndBordersForInlineLevelAndReplaced);
paint_node(m_box, context, PaintPhase::Foreground);
paint_descendants(context, m_box, StackingContextPaintPhase::Foreground);
paint_descendants(context, paintable_box(), StackingContextPaintPhase::BackgroundAndBordersForInlineLevelAndReplaced);
paint_node(paintable_box(), context, PaintPhase::Foreground);
paint_descendants(context, paintable_box(), StackingContextPaintPhase::Foreground);
// Draw positioned descendants with z-index `0` or `auto` in tree order. (step 8)
// FIXME: There's more to this step that we have yet to understand and implement.
m_box->paintable_box()->for_each_in_subtree([&](Paintable const& paintable) {
auto const& layout_node = paintable.layout_node();
paintable_box().for_each_in_subtree([this, &context](Paintable const& paintable) {
auto const& z_index = paintable.computed_values().z_index();
if (!layout_node.is_positioned() || (z_index.has_value() && z_index.value() != 0)) {
if (!paintable.is_positioned() || (z_index.has_value() && z_index.value() != 0)) {
return paintable.stacking_context_rooted_here()
? TraversalDecision::SkipChildrenAndContinue
: TraversalDecision::Continue;
@ -218,11 +203,10 @@ void StackingContext::paint_internal(PaintContext& context) const
// At this point, `paintable_box` is a positioned descendant with z-index: auto.
// FIXME: This is basically duplicating logic found elsewhere in this same function. Find a way to make this more elegant.
auto parent = layout_node.parent();
auto* parent_paintable = parent ? parent->paintable() : nullptr;
auto* parent_paintable = paintable.parent();
if (parent_paintable)
parent_paintable->before_children_paint(context, PaintPhase::Foreground);
auto containing_block = layout_node.containing_block();
auto containing_block = paintable.containing_block();
auto* containing_block_paintable = containing_block ? containing_block->paintable() : nullptr;
if (containing_block_paintable)
containing_block_paintable->apply_clip_overflow_rect(context, PaintPhase::Foreground);
@ -230,16 +214,16 @@ void StackingContext::paint_internal(PaintContext& context) const
paint_child(context, *child);
return TraversalDecision::SkipChildrenAndContinue;
} else {
paint_node(layout_node, context, PaintPhase::Background);
paint_node(layout_node, context, PaintPhase::Border);
paint_descendants(context, layout_node, StackingContextPaintPhase::BackgroundAndBorders);
paint_descendants(context, layout_node, StackingContextPaintPhase::Floats);
paint_descendants(context, layout_node, StackingContextPaintPhase::BackgroundAndBordersForInlineLevelAndReplaced);
paint_node(layout_node, context, PaintPhase::Foreground);
paint_descendants(context, layout_node, StackingContextPaintPhase::Foreground);
paint_node(layout_node, context, PaintPhase::Outline);
paint_node(layout_node, context, PaintPhase::Overlay);
paint_descendants(context, layout_node, StackingContextPaintPhase::FocusAndOverlay);
paint_node(paintable, context, PaintPhase::Background);
paint_node(paintable, context, PaintPhase::Border);
paint_descendants(context, paintable, StackingContextPaintPhase::BackgroundAndBorders);
paint_descendants(context, paintable, StackingContextPaintPhase::Floats);
paint_descendants(context, paintable, StackingContextPaintPhase::BackgroundAndBordersForInlineLevelAndReplaced);
paint_node(paintable, context, PaintPhase::Foreground);
paint_descendants(context, paintable, StackingContextPaintPhase::Foreground);
paint_node(paintable, context, PaintPhase::Outline);
paint_node(paintable, context, PaintPhase::Overlay);
paint_descendants(context, paintable, StackingContextPaintPhase::FocusAndOverlay);
}
if (parent_paintable)
parent_paintable->after_children_paint(context, PaintPhase::Foreground);
@ -252,15 +236,15 @@ void StackingContext::paint_internal(PaintContext& context) const
// Stacking contexts formed by positioned descendants with z-indices greater than or equal to 1 in z-index order
// (smallest first) then tree order. (Step 9)
for (auto* child : m_children) {
if (!child->paintable_box().layout_box().is_positioned())
if (!child->paintable_box().is_positioned())
continue;
if (child->paintable_box().computed_values().z_index().has_value() && child->m_box->computed_values().z_index().value() >= 1)
if (child->paintable_box().computed_values().z_index().has_value() && child->paintable_box().computed_values().z_index().value() >= 1)
paint_child(context, *child);
}
paint_node(m_box, context, PaintPhase::Outline);
paint_node(m_box, context, PaintPhase::Overlay);
paint_descendants(context, m_box, StackingContextPaintPhase::FocusAndOverlay);
paint_node(paintable_box(), context, PaintPhase::Outline);
paint_node(paintable_box(), context, PaintPhase::Overlay);
paint_descendants(context, paintable_box(), StackingContextPaintPhase::FocusAndOverlay);
}
Gfx::FloatMatrix4x4 StackingContext::get_transformation_matrix(CSS::Transformation const& transformation) const
@ -269,10 +253,10 @@ Gfx::FloatMatrix4x4 StackingContext::get_transformation_matrix(CSS::Transformati
auto value = [this, transformation](size_t index, CSS::Length const& reference_length = CSS::Length::make_px(0)) -> float {
return transformation.values[index].visit(
[this, reference_length](CSS::LengthPercentage const& value) -> double {
return value.resolved(m_box, reference_length).to_px(m_box).to_float();
return value.resolved(paintable_box().layout_node(), reference_length).to_px(paintable_box().layout_box()).to_float();
},
[this](CSS::AngleOrCalculated const& value) {
return value.resolved(m_box).to_degrees() * M_DEG2RAD;
return value.resolved(paintable_box().layout_node()).to_degrees() * M_DEG2RAD;
},
[](double value) {
return value;
@ -422,11 +406,11 @@ Gfx::AffineTransform StackingContext::affine_transform_matrix() const
void StackingContext::paint(PaintContext& context) const
{
Gfx::PainterStateSaver saver(context.painter());
if (m_box->is_fixed_position()) {
if (paintable_box().is_fixed_position()) {
context.painter().translate(-context.painter().translation());
}
auto opacity = m_box->computed_values().opacity();
auto opacity = paintable_box().computed_values().opacity();
if (opacity == 0.0f)
return;
@ -473,7 +457,7 @@ void StackingContext::paint(PaintContext& context) const
if (destination_rect.size() == bitmap->size()) {
context.painter().blit(destination_rect.location(), *bitmap, bitmap->rect(), opacity);
} else {
auto scaling_mode = CSS::to_gfx_scaling_mode(m_box->computed_values().image_rendering(), bitmap->rect(), destination_rect);
auto scaling_mode = CSS::to_gfx_scaling_mode(paintable_box().computed_values().image_rendering(), bitmap->rect(), destination_rect);
context.painter().draw_scaled_bitmap(destination_rect, *bitmap, bitmap->rect(), opacity, scaling_mode);
}
} else {
@ -485,11 +469,11 @@ void StackingContext::paint(PaintContext& context) const
Gfx::FloatPoint StackingContext::compute_transform_origin() const
{
auto style_value = m_box->computed_values().transform_origin();
auto style_value = paintable_box().computed_values().transform_origin();
// FIXME: respect transform-box property
auto reference_box = paintable_box().absolute_border_box_rect();
auto x = reference_box.left() + style_value.x.to_px(m_box, reference_box.width());
auto y = reference_box.top() + style_value.y.to_px(m_box, reference_box.height());
auto x = reference_box.left() + style_value.x.to_px(paintable_box().layout_node(), reference_box.width());
auto y = reference_box.top() + style_value.y.to_px(paintable_box().layout_node(), reference_box.height());
return { x.to_float(), y.to_float() };
}
@ -525,7 +509,7 @@ static TraversalDecision for_each_in_subtree_of_type_within_same_stacking_contex
Optional<HitTestResult> StackingContext::hit_test(CSSPixelPoint position, HitTestType type) const
{
if (!m_box->is_visible())
if (!paintable_box().is_visible())
return {};
auto transform_origin = this->transform_origin().to_type<CSSPixels>();
@ -536,7 +520,7 @@ Optional<HitTestResult> StackingContext::hit_test(CSSPixelPoint position, HitTes
};
auto transformed_position = affine_transform_matrix().inverse().value_or({}).map(offset_position).to_type<CSSPixels>() + transform_origin;
if (paintable_box().layout_box().is_fixed_position()) {
if (paintable_box().is_fixed_position()) {
auto scroll_offset = paintable_box().document().browsing_context()->viewport_scroll_offset();
transformed_position.translate_by(-scroll_offset);
}
@ -554,7 +538,7 @@ Optional<HitTestResult> StackingContext::hit_test(CSSPixelPoint position, HitTes
// 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.paintable_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())
@ -571,8 +555,7 @@ Optional<HitTestResult> StackingContext::hit_test(CSSPixelPoint position, HitTes
}
auto const& z_index = paintable_box.computed_values().z_index();
auto& layout_box = paintable_box.layout_box();
if (z_index.value_or(0) == 0 && layout_box.is_positioned() && !paintable_box.stacking_context()) {
if (z_index.value_or(0) == 0 && paintable_box.is_positioned() && !paintable_box.stacking_context()) {
auto candidate = paintable_box.hit_test(transformed_position, type);
if (candidate.has_value() && candidate->paintable->visible_for_hit_testing()) {
result = move(candidate);
@ -596,7 +579,7 @@ Optional<HitTestResult> StackingContext::hit_test(CSSPixelPoint position, HitTes
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)) {
if (paintable_box().layout_box().children_are_inline() && is<Layout::BlockContainer>(paintable_box().layout_box())) {
auto result = paintable_box().hit_test(transformed_position, type);
if (result.has_value() && result->paintable->visible_for_hit_testing())
return result;
@ -610,8 +593,7 @@ Optional<HitTestResult> StackingContext::hit_test(CSSPixelPoint position, HitTes
return TraversalDecision::SkipChildrenAndContinue;
}
auto& layout_box = paintable_box.layout_box();
if (layout_box.is_floating()) {
if (paintable_box.is_floating()) {
if (auto candidate = paintable_box.hit_test(transformed_position, type); candidate.has_value()) {
result = move(candidate);
return TraversalDecision::Break;
@ -623,7 +605,7 @@ Optional<HitTestResult> StackingContext::hit_test(CSSPixelPoint position, HitTes
return result;
// 3. the in-flow, non-inline-level, non-positioned descendants.
if (!m_box->children_are_inline()) {
if (!paintable_box().layout_box().children_are_inline()) {
for_each_in_subtree_of_type_within_same_stacking_context_in_reverse<PaintableBox>(paintable_box(), [&](PaintableBox const& paintable_box) {
// FIXME: Support more overflow variations.
if (paintable_box.computed_values().overflow_x() == CSS::Overflow::Hidden && paintable_box.computed_values().overflow_y() == CSS::Overflow::Hidden) {
@ -631,8 +613,7 @@ Optional<HitTestResult> StackingContext::hit_test(CSSPixelPoint position, HitTes
return TraversalDecision::SkipChildrenAndContinue;
}
auto& layout_box = paintable_box.layout_box();
if (!layout_box.is_absolutely_positioned() && !layout_box.is_floating()) {
if (!paintable_box.is_absolutely_positioned() && !paintable_box.is_floating()) {
if (auto candidate = paintable_box.hit_test(transformed_position, type); candidate.has_value()) {
result = move(candidate);
return TraversalDecision::Break;
@ -648,7 +629,7 @@ Optional<HitTestResult> StackingContext::hit_test(CSSPixelPoint position, HitTes
// 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.paintable_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())
@ -670,9 +651,9 @@ void StackingContext::dump(int indent) const
StringBuilder builder;
for (int i = 0; i < indent; ++i)
builder.append(' ');
builder.appendff("SC for {} {} [children: {}] (z-index: ", m_box->debug_description(), paintable_box().absolute_rect(), m_children.size());
if (m_box->computed_values().z_index().has_value())
builder.appendff("{}", m_box->computed_values().z_index().value());
builder.appendff("SC for {} {} [children: {}] (z-index: ", paintable_box().layout_box().debug_description(), paintable_box().absolute_rect(), m_children.size());
if (paintable_box().computed_values().z_index().has_value())
builder.appendff("{}", paintable_box().computed_values().z_index().value());
else
builder.append("auto"sv);
builder.append(')');

View file

@ -8,19 +8,18 @@
#include <AK/Vector.h>
#include <LibGfx/Matrix4x4.h>
#include <LibWeb/Layout/Node.h>
#include <LibWeb/Painting/Paintable.h>
namespace Web::Painting {
class StackingContext {
public:
StackingContext(Layout::Box&, StackingContext* parent, size_t index_in_tree_order);
StackingContext(PaintableBox&, StackingContext* parent, size_t index_in_tree_order);
StackingContext* parent() { return m_parent; }
StackingContext const* parent() const { return m_parent; }
PaintableBox const& paintable_box() const { return *m_box->paintable_box(); }
PaintableBox const& paintable_box() const { return *m_paintable_box; }
enum class StackingContextPaintPhase {
BackgroundAndBorders,
@ -30,7 +29,7 @@ public:
FocusAndOverlay,
};
void paint_descendants(PaintContext&, Layout::Node const&, StackingContextPaintPhase) const;
void paint_descendants(PaintContext&, Paintable const&, StackingContextPaintPhase) const;
void paint(PaintContext&) const;
Optional<HitTestResult> hit_test(CSSPixelPoint, HitTestType) const;
@ -42,7 +41,7 @@ public:
void sort();
private:
JS::NonnullGCPtr<Layout::Box> m_box;
JS::NonnullGCPtr<PaintableBox> m_paintable_box;
Gfx::FloatMatrix4x4 m_transform;
Gfx::FloatPoint m_transform_origin;
StackingContext* const m_parent { nullptr };

View file

@ -30,16 +30,15 @@ struct Traits<CellCoordinates> : public GenericTraits<CellCoordinates> {
namespace Web::Painting {
static void collect_cell_boxes(Vector<PaintableBox const*>& cell_boxes, Layout::Node const& box)
static void collect_cell_boxes(Vector<PaintableBox const*>& cell_boxes, PaintableBox const& table_paintable)
{
box.for_each_child([&](auto& child) {
table_paintable.for_each_child_of_type<PaintableBox>([&](auto& child) {
if (child.display().is_table_cell()) {
VERIFY(is<Layout::Box>(child));
if (child.paintable())
cell_boxes.append(static_cast<Layout::Box const&>(child).paintable_box());
cell_boxes.append(&child);
} else {
collect_cell_boxes(cell_boxes, child);
}
return TraversalDecision::Continue;
});
}
@ -356,12 +355,12 @@ static void paint_separate_cell_borders(PaintableBox const* cell_box, HashMap<Ce
paint_all_borders(context, cell_rect, cell_box->normalized_border_radii_data(), borders_data);
}
void paint_table_borders(PaintContext& context, Layout::Node const& box)
void paint_table_borders(PaintContext& context, PaintableBox const& table_paintable)
{
// Partial implementation of painting according to the collapsing border model:
// https://www.w3.org/TR/CSS22/tables.html#collapsing-borders
Vector<PaintableBox const*> cell_boxes;
collect_cell_boxes(cell_boxes, box);
collect_cell_boxes(cell_boxes, table_paintable);
Vector<BorderEdgePaintingInfo> border_edge_painting_info_list;
HashMap<CellCoordinates, PaintableBox const*> cell_coordinates_to_box;
size_t row_count = 0;

View file

@ -10,6 +10,6 @@
namespace Web::Painting {
void paint_table_borders(PaintContext&, Layout::Node const&);
void paint_table_borders(PaintContext&, PaintableBox const& table_paintable);
}

View file

@ -31,7 +31,7 @@ void ViewportPaintable::build_stacking_context_tree_if_needed()
void ViewportPaintable::build_stacking_context_tree()
{
set_stacking_context(make<StackingContext>(layout_box(), nullptr, 0));
set_stacking_context(make<StackingContext>(*this, nullptr, 0));
size_t index_in_tree_order = 1;
for_each_in_subtree_of_type<PaintableBox>([&](PaintableBox const& paintable) {
@ -43,7 +43,7 @@ void ViewportPaintable::build_stacking_context_tree()
}
auto* parent_context = paintable_box.enclosing_stacking_context();
VERIFY(parent_context);
paintable_box.set_stacking_context(make<Painting::StackingContext>(paintable_box.layout_box(), parent_context, index_in_tree_order++));
paintable_box.set_stacking_context(make<Painting::StackingContext>(paintable_box, parent_context, index_in_tree_order++));
return TraversalDecision::Continue;
});