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ladybird/Userland/Libraries/LibWeb/Painting/StackingContext.cpp
Aliaksandr Kalenik 5484062095 LibWeb: Apply scroll offset to PushStackingContext command 
In cases where the stacking context painting requires a separate
bitmap, the destination position needs to be translated by the
scrolling offset to ensure it ends up in the correct position.
2024-02-01 13:38:45 +01:00

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/*
* Copyright (c) 2020-2022, Andreas Kling <kling@serenityos.org>
* Copyright (c) 2022, Sam Atkins <atkinssj@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/Debug.h>
#include <AK/QuickSort.h>
#include <AK/StringBuilder.h>
#include <LibGfx/AffineTransform.h>
#include <LibGfx/Matrix4x4.h>
#include <LibGfx/Rect.h>
#include <LibWeb/CSS/ComputedValues.h>
#include <LibWeb/CSS/StyleValues/TransformationStyleValue.h>
#include <LibWeb/Layout/Box.h>
#include <LibWeb/Layout/ReplacedBox.h>
#include <LibWeb/Layout/Viewport.h>
#include <LibWeb/Painting/PaintableBox.h>
#include <LibWeb/Painting/SVGPaintable.h>
#include <LibWeb/Painting/StackingContext.h>
#include <LibWeb/Painting/TableBordersPainting.h>
#include <LibWeb/SVG/SVGMaskElement.h>
namespace Web::Painting {
static void paint_node(Paintable const& paintable, PaintContext& context, PaintPhase phase)
{
paintable.before_paint(context, phase);
paintable.paint(context, phase);
paintable.after_paint(context, phase);
}
StackingContext::StackingContext(Paintable& paintable, StackingContext* parent, size_t index_in_tree_order)
: m_paintable(paintable)
, m_parent(parent)
, m_index_in_tree_order(index_in_tree_order)
{
VERIFY(m_parent != this);
if (m_parent)
m_parent->m_children.append(this);
}
void StackingContext::sort()
{
quick_sort(m_children, [](auto& a, auto& b) {
auto a_z_index = a->paintable().computed_values().z_index().value_or(0);
auto b_z_index = b->paintable().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;
});
for (auto* child : m_children)
child->sort();
}
static PaintPhase to_paint_phase(StackingContext::StackingContextPaintPhase phase)
{
// There are not a fully correct mapping since some stacking context phases are combined.
switch (phase) {
case StackingContext::StackingContextPaintPhase::Floats:
case StackingContext::StackingContextPaintPhase::BackgroundAndBordersForInlineLevelAndReplaced:
case StackingContext::StackingContextPaintPhase::BackgroundAndBorders:
return PaintPhase::Background;
case StackingContext::StackingContextPaintPhase::Foreground:
return PaintPhase::Foreground;
case StackingContext::StackingContextPaintPhase::FocusAndOverlay:
return PaintPhase::Overlay;
default:
VERIFY_NOT_REACHED();
}
}
void StackingContext::paint_node_as_stacking_context(Paintable const& paintable, PaintContext& context)
{
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);
}
void StackingContext::paint_descendants(PaintContext& context, Paintable const& paintable, StackingContextPaintPhase phase)
{
paintable.before_children_paint(context, to_paint_phase(phase));
paintable.for_each_child([&context, phase](auto& child) {
auto* stacking_context = child.stacking_context();
auto const& z_index = child.computed_values().z_index();
// NOTE: Grid specification https://www.w3.org/TR/css-grid-2/#z-order says that grid items should be treated
// the same way as CSS2 defines for inline-blocks:
// "For each one of these, treat the element as if it created a new stacking context, but any positioned
// descendants and descendants which actually create a new stacking context should be considered part of
// the parent stacking context, not this new one."
auto should_be_treated_as_stacking_context = child.layout_node().is_grid_item() && !z_index.has_value();
if (should_be_treated_as_stacking_context) {
// FIXME: This may not be fully correct with respect to the paint phases.
if (phase == StackingContextPaintPhase::Foreground)
paint_node_as_stacking_context(child, context);
return;
}
if (stacking_context && z_index.has_value())
return;
if (child.is_positioned() && !z_index.has_value())
return;
if (stacking_context) {
// FIXME: This may not be fully correct with respect to the paint phases.
if (phase == StackingContextPaintPhase::Foreground) {
paint_child(context, *stacking_context);
}
// Note: Don't further recurse into descendants as paint_child() will do that.
return;
}
bool child_is_inline_or_replaced = child.is_inline() || is<Layout::ReplacedBox>(child);
switch (phase) {
case StackingContextPaintPhase::BackgroundAndBorders:
if (!child_is_inline_or_replaced && !child.is_floating()) {
paint_node(child, context, PaintPhase::Background);
bool is_table_with_collapsed_borders = child.display().is_table_inside() && child.computed_values().border_collapse() == CSS::BorderCollapse::Collapse;
if (!child.display().is_table_cell() && !is_table_with_collapsed_borders)
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, verify_cast<PaintableBox>(child));
}
}
break;
case StackingContextPaintPhase::Floats:
if (child.is_floating()) {
paint_node(child, context, PaintPhase::Background);
paint_node(child, context, PaintPhase::Border);
paint_descendants(context, child, StackingContextPaintPhase::BackgroundAndBorders);
}
paint_descendants(context, child, phase);
break;
case StackingContextPaintPhase::BackgroundAndBordersForInlineLevelAndReplaced:
if (child_is_inline_or_replaced) {
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, verify_cast<PaintableBox>(child));
paint_descendants(context, child, StackingContextPaintPhase::BackgroundAndBorders);
}
paint_descendants(context, child, phase);
break;
case StackingContextPaintPhase::Foreground:
paint_node(child, context, PaintPhase::Foreground);
paint_descendants(context, child, phase);
break;
case StackingContextPaintPhase::FocusAndOverlay:
paint_node(child, context, PaintPhase::Outline);
paint_node(child, context, PaintPhase::Overlay);
paint_descendants(context, child, phase);
break;
}
});
paintable.after_children_paint(context, to_paint_phase(phase));
}
void StackingContext::paint_child(PaintContext& context, StackingContext const& child)
{
auto parent_paintable = child.paintable().parent();
if (parent_paintable)
parent_paintable->before_children_paint(context, PaintPhase::Foreground);
child.paint(context);
if (parent_paintable)
parent_paintable->after_children_paint(context, PaintPhase::Foreground);
}
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(paintable(), context, PaintPhase::Background);
paint_node(paintable(), 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)
// NOTE: This doesn't check if a descendant is positioned as modern CSS allows for alternative methods to establish stacking contexts.
for (auto* child : m_children) {
if (child->paintable().computed_values().z_index().has_value() && child->paintable().computed_values().z_index().value() < 0)
paint_child(context, *child);
}
// Draw the background and borders for block-level children (step 4)
paint_descendants(context, paintable(), StackingContextPaintPhase::BackgroundAndBorders);
// Draw the non-positioned floats (step 5)
paint_descendants(context, paintable(), StackingContextPaintPhase::Floats);
// Draw inline content, replaced content, etc. (steps 6, 7)
paint_descendants(context, paintable(), StackingContextPaintPhase::BackgroundAndBordersForInlineLevelAndReplaced);
paint_node(paintable(), context, PaintPhase::Foreground);
paint_descendants(context, paintable(), 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.
paintable().for_each_in_subtree([&context](Paintable const& paintable) {
auto const& z_index = paintable.computed_values().z_index();
if (!paintable.is_positioned() || (z_index.has_value() && z_index.value() != 0)) {
return paintable.stacking_context()
? TraversalDecision::SkipChildrenAndContinue
: TraversalDecision::Continue;
}
// 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 exit_decision = TraversalDecision::Continue;
auto* parent_paintable = paintable.parent();
if (parent_paintable)
parent_paintable->before_children_paint(context, PaintPhase::Foreground);
if (auto* child = paintable.stacking_context()) {
paint_child(context, *child);
exit_decision = TraversalDecision::SkipChildrenAndContinue;
} else {
paint_node_as_stacking_context(paintable, context);
}
if (parent_paintable)
parent_paintable->after_children_paint(context, PaintPhase::Foreground);
return exit_decision;
});
// 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)
// NOTE: This doesn't check if a descendant is positioned as modern CSS allows for alternative methods to establish stacking contexts.
for (auto* child : m_children) {
if (child->paintable().computed_values().z_index().has_value() && child->paintable().computed_values().z_index().value() >= 1)
paint_child(context, *child);
}
paint_node(paintable(), context, PaintPhase::Outline);
if (context.should_paint_overlay()) {
paint_node(paintable(), context, PaintPhase::Overlay);
paint_descendants(context, paintable(), StackingContextPaintPhase::FocusAndOverlay);
}
}
// FIXME: This extracts the affine 2D part of the full transformation matrix.
// Use the whole matrix when we get better transformation support in LibGfx or use LibGL for drawing the bitmap
Gfx::AffineTransform StackingContext::affine_transform_matrix() const
{
if (paintable().is_paintable_box())
return Gfx::extract_2d_affine_transform(paintable_box().transform());
return Gfx::AffineTransform {};
}
static Gfx::FloatMatrix4x4 matrix_with_scaled_translation(Gfx::FloatMatrix4x4 matrix, float scale)
{
auto* m = matrix.elements();
m[0][3] *= scale;
m[1][3] *= scale;
m[2][3] *= scale;
return matrix;
}
void StackingContext::paint(PaintContext& context) const
{
auto opacity = paintable().computed_values().opacity();
if (opacity == 0.0f)
return;
RecordingPainterStateSaver saver(context.recording_painter());
auto to_device_pixels_scale = float(context.device_pixels_per_css_pixel());
Gfx::IntRect source_paintable_rect;
if (paintable().is_paintable_box()) {
source_paintable_rect = context.enclosing_device_rect(paintable_box().absolute_paint_rect()).to_type<int>();
} else if (paintable().is_inline()) {
source_paintable_rect = context.enclosing_device_rect(inline_paintable().bounding_rect()).to_type<int>();
} else {
VERIFY_NOT_REACHED();
}
auto transform_matrix = Gfx::FloatMatrix4x4::identity();
Gfx::FloatPoint transform_origin;
if (paintable().is_paintable_box()) {
transform_matrix = paintable_box().transform();
transform_origin = paintable_box().transform_origin().to_type<float>();
}
RecordingPainter::PushStackingContextParams push_stacking_context_params {
.opacity = opacity,
.is_fixed_position = paintable().is_fixed_position(),
.source_paintable_rect = source_paintable_rect,
.image_rendering = paintable().computed_values().image_rendering(),
.transform = {
.origin = transform_origin.scaled(to_device_pixels_scale),
.matrix = matrix_with_scaled_translation(transform_matrix, to_device_pixels_scale),
},
};
if (paintable().is_paintable_box()) {
if (auto masking_area = paintable_box().get_masking_area(); masking_area.has_value()) {
if (masking_area->is_empty())
return;
auto mask_bitmap = paintable_box().calculate_mask(context, *masking_area);
if (mask_bitmap) {
auto source_paintable_rect = context.enclosing_device_rect(*masking_area).to_type<int>();
push_stacking_context_params.source_paintable_rect = source_paintable_rect;
push_stacking_context_params.mask = StackingContextMask {
.mask_bitmap = mask_bitmap.release_nonnull(),
.mask_kind = *paintable_box().get_mask_type()
};
}
}
}
context.recording_painter().save();
if (paintable().is_paintable_box() && paintable_box().scroll_frame_id().has_value())
context.recording_painter().set_scroll_frame_id(*paintable_box().scroll_frame_id());
context.recording_painter().push_stacking_context(push_stacking_context_params);
paint_internal(context);
context.recording_painter().pop_stacking_context();
context.recording_painter().restore();
}
template<typename Callback>
static TraversalDecision for_each_in_inclusive_subtree_within_same_stacking_context_in_reverse(Paintable const& paintable, Callback callback)
{
if (paintable.stacking_context()) {
// Note: Include the stacking context (so we can hit test it), but don't recurse into it.
if (auto decision = callback(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_within_same_stacking_context_in_reverse(*child, callback) == TraversalDecision::Break)
return TraversalDecision::Break;
}
if (auto decision = callback(paintable); decision != TraversalDecision::Continue)
return decision;
return TraversalDecision::Continue;
}
template<typename Callback>
static TraversalDecision for_each_in_subtree_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_within_same_stacking_context_in_reverse(*child, callback) == TraversalDecision::Break)
return TraversalDecision::Break;
}
return TraversalDecision::Continue;
}
Optional<HitTestResult> StackingContext::hit_test(CSSPixelPoint position, HitTestType type) const
{
if (!paintable().is_visible())
return {};
CSSPixelPoint transform_origin { 0, 0 };
if (paintable().is_paintable_box())
transform_origin = paintable_box().transform_origin();
// NOTE: This CSSPixels -> Float -> CSSPixels conversion is because we can't AffineTransform::map() a CSSPixelPoint.
Gfx::FloatPoint offset_position {
(position.x() - transform_origin.x()).to_float(),
(position.y() - transform_origin.y()).to_float()
};
auto transformed_position = affine_transform_matrix().inverse().value_or({}).map(offset_position).to_type<CSSPixels>() + transform_origin;
if (paintable().is_fixed_position()) {
auto scroll_offset = paintable().document().navigable()->viewport_scroll_offset();
transformed_position.translate_by(-scroll_offset);
}
// NOTE: Hit testing basically happens in reverse painting order.
// https://www.w3.org/TR/CSS22/visuren.html#z-index
// 7. the child stacking contexts with positive stack levels (least positive first).
// 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.paintable().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;
}
// 6. the child stacking contexts with stack level 0 and the positioned descendants with stack level 0.
Optional<HitTestResult> result;
for_each_in_subtree_within_same_stacking_context_in_reverse(paintable(), [&](Paintable const& paintable) {
if (!paintable.is_paintable_box())
return TraversalDecision::Continue;
auto const& paintable_box = verify_cast<PaintableBox>(paintable);
auto const& z_index = paintable_box.computed_values().z_index();
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);
return TraversalDecision::Break;
}
}
if (paintable_box.stacking_context()) {
if (z_index.value_or(0) == 0) {
auto candidate = paintable_box.stacking_context()->hit_test(transformed_position, type);
if (candidate.has_value() && candidate->paintable->visible_for_hit_testing()) {
result = move(candidate);
return TraversalDecision::Break;
}
}
}
return TraversalDecision::Continue;
});
if (result.has_value())
return result;
// 5. the in-flow, inline-level, non-positioned descendants, including inline tables and inline blocks.
if (paintable().layout_node().children_are_inline() && is<Layout::BlockContainer>(paintable().layout_node())) {
auto result = paintable_box().hit_test(transformed_position, type);
if (result.has_value() && result->paintable->visible_for_hit_testing())
return result;
}
// 4. the non-positioned floats.
for_each_in_subtree_within_same_stacking_context_in_reverse(paintable(), [&](Paintable const& paintable) {
if (!paintable.is_paintable_box())
return TraversalDecision::Continue;
auto const& paintable_box = verify_cast<PaintableBox>(paintable);
if (paintable_box.is_floating()) {
if (auto candidate = paintable_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())
return result;
// 3. the in-flow, non-inline-level, non-positioned descendants.
if (!paintable().layout_node().children_are_inline()) {
for_each_in_subtree_within_same_stacking_context_in_reverse(paintable(), [&](Paintable const& paintable) {
if (!paintable.is_paintable_box())
return TraversalDecision::Continue;
auto const& paintable_box = verify_cast<PaintableBox>(paintable);
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;
}
}
return TraversalDecision::Continue;
});
if (result.has_value() && result->paintable->visible_for_hit_testing())
return result;
}
// 2. the child stacking contexts with negative stack levels (most negative first).
// 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.paintable().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;
}
// 1. the background and borders of the element forming the stacking context.
if (paintable().is_paintable_box()) {
if (paintable_box().absolute_border_box_rect().contains(transformed_position.x(), transformed_position.y())) {
return HitTestResult {
.paintable = const_cast<PaintableBox&>(paintable_box()),
};
}
}
return {};
}
void StackingContext::dump(int indent) const
{
StringBuilder builder;
for (int i = 0; i < indent; ++i)
builder.append(' ');
CSSPixelRect rect;
if (paintable().is_paintable_box()) {
rect = paintable_box().absolute_rect();
} else if (paintable().is_inline_paintable()) {
rect = inline_paintable().bounding_rect();
} else {
VERIFY_NOT_REACHED();
}
builder.appendff("SC for {} {} [children: {}] (z-index: ", paintable().layout_node().debug_description(), rect, m_children.size());
if (paintable().computed_values().z_index().has_value())
builder.appendff("{}", paintable().computed_values().z_index().value());
else
builder.append("auto"sv);
builder.append(')');
auto affine_transform = affine_transform_matrix();
if (!affine_transform.is_identity()) {
builder.appendff(", transform: {}", affine_transform);
}
dbgln("{}", builder.string_view());
for (auto& child : m_children)
child->dump(indent + 1);
}
}
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