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LibWeb: Special case SVG masks during layout

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Rather than try to lay out masks normally, this updates the TreeBuilder
to create layout nodes for masks as a child of their user (i.e. the
masked element). This allows each use of a mask to be laid out
differently, which makes supporting `maskContentUnits=objectBoundingBox`
fairly easy.

The `SVGFormattingContext` is then updated to lay out masks last (as
their sizing may depend on their parent), and treats them like
viewports.

This is pretty ad-hoc, but the SVG specification does not give any
guidance on how to actually implement this.
This commit is contained in:
MacDue 2024-03-11 18:26:58 +00:00 • committed by Andreas Kling
parent 15e3b0ebde
commit 163b6bb401
18 changed files with 232 additions and 76 deletions
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38
Userland/Libraries/LibWeb/Layout/SVGFormattingContext.cpp
View file

@ -14,6 +14,7 @@
#include <LibWeb/Layout/BlockFormattingContext.h>
#include <LibWeb/Layout/SVGFormattingContext.h>
#include <LibWeb/Layout/SVGGeometryBox.h>
#include <LibWeb/Layout/SVGMaskBox.h>
#include <LibWeb/Layout/SVGSVGBox.h>
#include <LibWeb/Layout/SVGTextBox.h>
#include <LibWeb/Layout/SVGTextPathBox.h>
@ -289,6 +290,8 @@ void SVGFormattingContext::run(Box const& box, LayoutMode layout_mode, Available
}();
for_each_in_subtree(box, [&](Node const& descendant) {
if (is<SVGMaskBox>(descendant))
return TraversalDecision::SkipChildrenAndContinue;
if (is<SVG::SVGViewport>(descendant.dom_node())) {
// Layout for a nested SVG viewport.
// https://svgwg.org/svg2-draft/coords.html#EstablishingANewSVGViewport.
@ -391,14 +394,19 @@ void SVGFormattingContext::run(Box const& box, LayoutMode layout_mode, Available
// https://svgwg.org/svg2-draft/struct.html#Groups
// 5.2. Grouping: the ‘g’ element
// The ‘g’ element is a container element for grouping together related graphics elements.
box.for_each_in_subtree_of_type<Box>([&](Box const& descendant) {
box.for_each_in_subtree_of_type<SVGBox>([&](SVGBox const& descendant) {
if (is_container_element(descendant)) {
Gfx::BoundingBox<CSSPixels> bounding_box;
descendant.for_each_in_subtree_of_type<Box>([&](Box const& child_of_svg_container) {
auto& box_state = m_state.get(child_of_svg_container);
for_each_in_subtree(descendant, [&](Node const& child_of_svg_container) {
if (!is<SVGBox>(child_of_svg_container))
return TraversalDecision::Continue;
// Masks do not change the bounding box of their parents.
if (is<SVGMaskBox>(child_of_svg_container))
return TraversalDecision::SkipChildrenAndContinue;
auto& box_state = m_state.get(static_cast<SVGBox const&>(child_of_svg_container));
bounding_box.add_point(box_state.offset);
bounding_box.add_point(box_state.offset.translated(box_state.content_width(), box_state.content_height()));
return IterationDecision::Continue;
return TraversalDecision::Continue;
});
auto& box_state = m_state.get_mutable(descendant);
@ -411,6 +419,28 @@ void SVGFormattingContext::run(Box const& box, LayoutMode layout_mode, Available
}
return IterationDecision::Continue;
});
// Lay out masks last (as their parent needs to be sized first).
box.for_each_in_subtree_of_type<SVGMaskBox>([&](SVGMaskBox const& mask_box) {
auto& mask_state = m_state.get_mutable(static_cast<Box const&>(mask_box));
auto parent_viewbox_transform = viewbox_transform;
if (mask_box.dom_node().mask_content_units() == SVG::MaskContentUnits::ObjectBoundingBox) {
auto* masked_node = mask_box.parent();
auto& masked_node_state = m_state.get(*masked_node);
mask_state.set_content_width(masked_node_state.content_width());
mask_state.set_content_height(masked_node_state.content_height());
parent_viewbox_transform = Gfx::AffineTransform {}.translate(masked_node_state.offset.to_type<float>());
} else {
mask_state.set_content_width(viewport_width);
mask_state.set_content_height(viewport_height);
}
// Pretend masks are a viewport so we can scale the contents depending on the `maskContentUnits`.
SVGFormattingContext nested_context(m_state, static_cast<Box const&>(mask_box), this, parent_viewbox_transform);
mask_state.set_has_definite_width(true);
mask_state.set_has_definite_height(true);
nested_context.run(static_cast<Box const&>(mask_box), layout_mode, available_space);
return IterationDecision::Continue;
});
}
}