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ladybird/Userland/Libraries/LibWeb/Layout/SVGFormattingContext.cpp
MacDue 163b6bb401 LibWeb: Special case SVG masks during layout 
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.
2024-03-12 08:51:50 +01:00

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/*
* Copyright (c) 2021-2023, Andreas Kling <kling@serenityos.org>
* Copyright (c) 2022, Sam Atkins <atkinssj@serenityos.org>
* Copyright (c) 2022, Tobias Christiansen <tobyase@serenityos.org>
* Copyright (c) 2023, MacDue <macdue@dueutil.tech>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/Debug.h>
#include <LibGfx/BoundingBox.h>
#include <LibGfx/Font/ScaledFont.h>
#include <LibGfx/TextLayout.h>
#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>
#include <LibWeb/SVG/SVGForeignObjectElement.h>
#include <LibWeb/SVG/SVGGElement.h>
#include <LibWeb/SVG/SVGMaskElement.h>
#include <LibWeb/SVG/SVGSVGElement.h>
#include <LibWeb/SVG/SVGSymbolElement.h>
#include <LibWeb/SVG/SVGUseElement.h>
namespace Web::Layout {
SVGFormattingContext::SVGFormattingContext(LayoutState& state, Box const& box, FormattingContext* parent, Gfx::AffineTransform parent_viewbox_transform)
: FormattingContext(Type::SVG, state, box, parent)
, m_parent_viewbox_transform(parent_viewbox_transform)
{
}
SVGFormattingContext::~SVGFormattingContext() = default;
CSSPixels SVGFormattingContext::automatic_content_width() const
{
return 0;
}
CSSPixels SVGFormattingContext::automatic_content_height() const
{
return 0;
}
struct ViewBoxTransform {
CSSPixelPoint offset;
double scale_factor_x;
double scale_factor_y;
};
// https://svgwg.org/svg2-draft/coords.html#PreserveAspectRatioAttribute
static ViewBoxTransform scale_and_align_viewbox_content(SVG::PreserveAspectRatio const& preserve_aspect_ratio,
SVG::ViewBox const& view_box, Gfx::FloatSize viewbox_scale, auto const& svg_box_state)
{
ViewBoxTransform viewbox_transform {};
if (preserve_aspect_ratio.align == SVG::PreserveAspectRatio::Align::None) {
viewbox_transform.scale_factor_x = viewbox_scale.width();
viewbox_transform.scale_factor_y = viewbox_scale.height();
viewbox_transform.offset = {};
return viewbox_transform;
}
switch (preserve_aspect_ratio.meet_or_slice) {
case SVG::PreserveAspectRatio::MeetOrSlice::Meet:
// meet (the default) - Scale the graphic such that:
// - aspect ratio is preserved
// - the entire ‘viewBox’ is visible within the SVG viewport
// - the ‘viewBox’ is scaled up as much as possible, while still meeting the other criteria
viewbox_transform.scale_factor_x = viewbox_transform.scale_factor_y = min(viewbox_scale.width(), viewbox_scale.height());
break;
case SVG::PreserveAspectRatio::MeetOrSlice::Slice:
// slice - Scale the graphic such that:
// aspect ratio is preserved
// the entire SVG viewport is covered by the ‘viewBox’
// the ‘viewBox’ is scaled down as much as possible, while still meeting the other criteria
viewbox_transform.scale_factor_x = viewbox_transform.scale_factor_y = max(viewbox_scale.width(), viewbox_scale.height());
break;
default:
VERIFY_NOT_REACHED();
}
// Handle X alignment:
if (svg_box_state.has_definite_width()) {
switch (preserve_aspect_ratio.align) {
case SVG::PreserveAspectRatio::Align::xMinYMin:
case SVG::PreserveAspectRatio::Align::xMinYMid:
case SVG::PreserveAspectRatio::Align::xMinYMax:
// Align the <min-x> of the element's ‘viewBox’ with the smallest X value of the SVG viewport.
viewbox_transform.offset.translate_by(0, 0);
break;
case SVG::PreserveAspectRatio::Align::None: {
// Do not force uniform scaling. Scale the graphic content of the given element non-uniformly
// if necessary such that the element's bounding box exactly matches the SVG viewport rectangle.
// FIXME: None is unimplemented (treat as xMidYMid)
[[fallthrough]];
}
case SVG::PreserveAspectRatio::Align::xMidYMin:
case SVG::PreserveAspectRatio::Align::xMidYMid:
case SVG::PreserveAspectRatio::Align::xMidYMax:
// Align the midpoint X value of the element's ‘viewBox’ with the midpoint X value of the SVG viewport.
viewbox_transform.offset.translate_by((svg_box_state.content_width() - CSSPixels::nearest_value_for(view_box.width * viewbox_transform.scale_factor_x)) / 2, 0);
break;
case SVG::PreserveAspectRatio::Align::xMaxYMin:
case SVG::PreserveAspectRatio::Align::xMaxYMid:
case SVG::PreserveAspectRatio::Align::xMaxYMax:
// Align the <min-x>+<width> of the element's ‘viewBox’ with the maximum X value of the SVG viewport.
viewbox_transform.offset.translate_by((svg_box_state.content_width() - CSSPixels::nearest_value_for(view_box.width * viewbox_transform.scale_factor_x)), 0);
break;
default:
VERIFY_NOT_REACHED();
}
}
if (svg_box_state.has_definite_width()) {
switch (preserve_aspect_ratio.align) {
case SVG::PreserveAspectRatio::Align::xMinYMin:
case SVG::PreserveAspectRatio::Align::xMidYMin:
case SVG::PreserveAspectRatio::Align::xMaxYMin:
// Align the <min-y> of the element's ‘viewBox’ with the smallest Y value of the SVG viewport.
viewbox_transform.offset.translate_by(0, 0);
break;
case SVG::PreserveAspectRatio::Align::None: {
// Do not force uniform scaling. Scale the graphic content of the given element non-uniformly
// if necessary such that the element's bounding box exactly matches the SVG viewport rectangle.
// FIXME: None is unimplemented (treat as xMidYMid)
[[fallthrough]];
}
case SVG::PreserveAspectRatio::Align::xMinYMid:
case SVG::PreserveAspectRatio::Align::xMidYMid:
case SVG::PreserveAspectRatio::Align::xMaxYMid:
// Align the midpoint Y value of the element's ‘viewBox’ with the midpoint Y value of the SVG viewport.
viewbox_transform.offset.translate_by(0, (svg_box_state.content_height() - CSSPixels::nearest_value_for(view_box.height * viewbox_transform.scale_factor_y)) / 2);
break;
case SVG::PreserveAspectRatio::Align::xMinYMax:
case SVG::PreserveAspectRatio::Align::xMidYMax:
case SVG::PreserveAspectRatio::Align::xMaxYMax:
// Align the <min-y>+<height> of the element's ‘viewBox’ with the maximum Y value of the SVG viewport.
viewbox_transform.offset.translate_by(0, (svg_box_state.content_height() - CSSPixels::nearest_value_for(view_box.height * viewbox_transform.scale_factor_y)));
break;
default:
VERIFY_NOT_REACHED();
}
}
return viewbox_transform;
}
static bool is_container_element(Node const& node)
{
// https://svgwg.org/svg2-draft/struct.html#GroupsOverview
auto* dom_node = node.dom_node();
if (!dom_node)
return false;
if (is<SVG::SVGUseElement>(dom_node))
return true;
if (is<SVG::SVGSymbolElement>(dom_node))
return true;
if (is<SVG::SVGGElement>(dom_node))
return true;
if (is<SVG::SVGMaskElement>(dom_node))
return true;
return false;
}
enum class TraversalDecision {
Continue,
SkipChildrenAndContinue,
Break,
};
// FIXME: Add TraversalDecision::SkipChildrenAndContinue to TreeNode's implementation.
template<typename Callback>
static TraversalDecision for_each_in_inclusive_subtree(Layout::Node const& node, Callback callback)
{
if (auto decision = callback(node); decision != TraversalDecision::Continue)
return decision;
for (auto* child = node.first_child(); child; child = child->next_sibling()) {
if (for_each_in_inclusive_subtree(*child, callback) == TraversalDecision::Break)
return TraversalDecision::Break;
}
return TraversalDecision::Continue;
}
// FIXME: Add TraversalDecision::SkipChildrenAndContinue to TreeNode's implementation.
template<typename Callback>
static TraversalDecision for_each_in_subtree(Layout::Node const& node, Callback callback)
{
for (auto* child = node.first_child(); child; child = child->next_sibling()) {
if (for_each_in_inclusive_subtree(*child, callback) == TraversalDecision::Break)
return TraversalDecision::Break;
}
return TraversalDecision::Continue;
}
void SVGFormattingContext::run(Box const& box, LayoutMode layout_mode, AvailableSpace const& available_space)
{
// NOTE: SVG doesn't have a "formatting context" in the spec, but this is the most
// obvious way to drive SVG layout in our engine at the moment.
auto& svg_viewport = dynamic_cast<SVG::SVGViewport const&>(*box.dom_node());
auto& svg_box_state = m_state.get_mutable(box);
// NOTE: We consider all SVG root elements to have definite size in both axes.
// I'm not sure if this is good or bad, but our viewport transform logic depends on it.
svg_box_state.set_has_definite_width(true);
svg_box_state.set_has_definite_height(true);
auto viewbox = svg_viewport.view_box();
// https://svgwg.org/svg2-draft/coords.html#ViewBoxAttribute
if (viewbox.has_value()) {
if (viewbox->width < 0 || viewbox->height < 0) {
// A negative value for <width> or <height> is an error and invalidates the ‘viewBox’ attribute.
viewbox = {};
} else if (viewbox->width == 0 || viewbox->height == 0) {
// A value of zero disables rendering of the element.
return;
}
}
auto viewbox_transform = [&] {
if (!viewbox.has_value())
return m_parent_viewbox_transform;
// FIXME: This should allow just one of width or height to be specified.
// E.g. We should be able to layout <svg width="100%"> where height is unspecified/auto.
if (!svg_box_state.has_definite_width() || !svg_box_state.has_definite_height()) {
dbgln_if(LIBWEB_CSS_DEBUG, "FIXME: Attempting to layout indefinitely sized SVG with a viewbox -- this likely won't work!");
}
auto scale_width = svg_box_state.has_definite_width() ? svg_box_state.content_width() / viewbox->width : 1;
auto scale_height = svg_box_state.has_definite_height() ? svg_box_state.content_height() / viewbox->height : 1;
// The initial value for preserveAspectRatio is xMidYMid meet.
auto preserve_aspect_ratio = svg_viewport.preserve_aspect_ratio().value_or(SVG::PreserveAspectRatio {});
auto viewbox_offset_and_scale = scale_and_align_viewbox_content(preserve_aspect_ratio, *viewbox, { scale_width, scale_height }, svg_box_state);
CSSPixelPoint offset = viewbox_offset_and_scale.offset;
return Gfx::AffineTransform { m_parent_viewbox_transform }.multiply(Gfx::AffineTransform {}
.translate(offset.to_type<float>())
.scale(viewbox_offset_and_scale.scale_factor_x, viewbox_offset_and_scale.scale_factor_y)
.translate({ -viewbox->min_x, -viewbox->min_y }));
}();
if (svg_box_state.has_definite_width() && svg_box_state.has_definite_height()) {
// Scale the box of the viewport based on the parent's viewBox transform.
// The viewBox transform is always just a simple scale + offset.
// FIXME: Avoid converting SVG box to floats.
Gfx::FloatRect svg_rect = { svg_box_state.offset.to_type<float>(),
{ float(svg_box_state.content_width()), float(svg_box_state.content_height()) } };
svg_rect = m_parent_viewbox_transform.map(svg_rect);
svg_box_state.set_content_offset(svg_rect.location().to_type<CSSPixels>());
svg_box_state.set_content_width(CSSPixels(svg_rect.width()));
svg_box_state.set_content_height(CSSPixels(svg_rect.height()));
svg_box_state.set_has_definite_width(true);
svg_box_state.set_has_definite_height(true);
}
auto root_offset = svg_box_state.offset;
box.for_each_child_of_type<BlockContainer>([&](BlockContainer const& child_box) {
if (is<SVG::SVGForeignObjectElement>(child_box.dom_node())) {
Layout::BlockFormattingContext bfc(m_state, child_box, this);
bfc.run(child_box, LayoutMode::Normal, available_space);
auto& child_state = m_state.get_mutable(child_box);
child_state.set_content_offset(child_state.offset.translated(root_offset));
}
return IterationDecision::Continue;
});
auto viewport_width = [&] {
if (viewbox.has_value())
return CSSPixels::nearest_value_for(viewbox->width);
if (svg_box_state.has_definite_width())
return svg_box_state.content_width();
dbgln_if(LIBWEB_CSS_DEBUG, "FIXME: Failed to resolve width of SVG viewport!");
return CSSPixels {};
}();
auto viewport_height = [&] {
if (viewbox.has_value())
return CSSPixels::nearest_value_for(viewbox->height);
if (svg_box_state.has_definite_height())
return svg_box_state.content_height();
dbgln_if(LIBWEB_CSS_DEBUG, "FIXME: Failed to resolve height of SVG viewport!");
return CSSPixels {};
}();
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.
SVGFormattingContext nested_context(m_state, static_cast<Box const&>(descendant), this, viewbox_transform);
auto& nested_viewport_state = m_state.get_mutable(static_cast<Box const&>(descendant));
auto resolve_dimension = [](auto& node, auto size, auto reference_value) {
// The value auto for width and height on the ‘svg’ element is treated as 100%.
// https://svgwg.org/svg2-draft/geometry.html#Sizing
if (size.is_auto())
return reference_value;
return size.to_px(node, reference_value);
};
auto nested_viewport_x = descendant.computed_values().x().to_px(descendant, viewport_width);
auto nested_viewport_y = descendant.computed_values().y().to_px(descendant, viewport_height);
auto nested_viewport_width = resolve_dimension(descendant, descendant.computed_values().width(), viewport_width);
auto nested_viewport_height = resolve_dimension(descendant, descendant.computed_values().height(), viewport_height);
nested_viewport_state.set_content_offset({ nested_viewport_x, nested_viewport_y });
nested_viewport_state.set_content_width(nested_viewport_width);
nested_viewport_state.set_content_height(nested_viewport_height);
nested_viewport_state.set_has_definite_width(true);
nested_viewport_state.set_has_definite_height(true);
nested_context.run(static_cast<Box const&>(descendant), layout_mode, available_space);
return TraversalDecision::SkipChildrenAndContinue;
}
if (is<SVGGraphicsBox>(descendant)) {
auto const& graphics_box = static_cast<SVGGraphicsBox const&>(descendant);
auto& dom_node = const_cast<SVGGraphicsBox&>(graphics_box).dom_node();
auto& graphics_box_state = m_state.get_mutable(graphics_box);
auto svg_transform = dom_node.get_transform();
graphics_box_state.set_computed_svg_transforms(Painting::SVGGraphicsPaintable::ComputedTransforms(viewbox_transform, svg_transform));
auto to_css_pixels_transform = Gfx::AffineTransform {}.multiply(viewbox_transform).multiply(svg_transform);
Gfx::Path path;
if (is<SVGGeometryBox>(descendant)) {
path = static_cast<SVG::SVGGeometryElement&>(dom_node).get_path({ viewport_width, viewport_height });
} else if (is<SVGTextBox>(descendant)) {
auto& text_element = static_cast<SVG::SVGTextPositioningElement&>(dom_node);
auto& font = graphics_box.first_available_font();
auto text_contents = text_element.text_contents();
Utf8View text_utf8 { text_contents };
auto text_width = font.width(text_utf8);
auto text_offset = text_element.get_offset();
// https://svgwg.org/svg2-draft/text.html#TextAnchoringProperties
switch (text_element.text_anchor().value_or(SVG::TextAnchor::Start)) {
case SVG::TextAnchor::Start:
// The rendered characters are aligned such that the start of the resulting rendered text is at the initial
// current text position.
break;
case SVG::TextAnchor::Middle: {
// The rendered characters are shifted such that the geometric middle of the resulting rendered text
// (determined from the initial and final current text position before applying the text-anchor property)
// is at the initial current text position.
text_offset.translate_by(-text_width / 2, 0);
break;
}
case SVG::TextAnchor::End: {
// The rendered characters are shifted such that the end of the resulting rendered text (final current text
// position before applying the text-anchor property) is at the initial current text position.
text_offset.translate_by(-text_width, 0);
break;
}
default:
VERIFY_NOT_REACHED();
}
path.move_to(text_offset);
path.text(text_utf8, font);
} else if (is<SVGTextPathBox>(descendant)) {
auto& text_path_element = static_cast<SVG::SVGTextPathElement&>(dom_node);
auto path_or_shape = text_path_element.path_or_shape();
if (!path_or_shape)
return TraversalDecision::Continue;
auto& font = graphics_box.first_available_font();
auto text_contents = text_path_element.text_contents();
Utf8View text_utf8 { text_contents };
auto shape_path = const_cast<SVG::SVGGeometryElement&>(*path_or_shape).get_path({ viewport_width, viewport_height });
path = shape_path.place_text_along(text_utf8, font);
}
auto path_bounding_box = to_css_pixels_transform.map(path.bounding_box()).to_type<CSSPixels>();
// Stroke increases the path's size by stroke_width/2 per side.
CSSPixels stroke_width = CSSPixels::nearest_value_for(graphics_box.dom_node().visible_stroke_width() * viewbox_transform.x_scale());
path_bounding_box.inflate(stroke_width, stroke_width);
graphics_box_state.set_content_offset(path_bounding_box.top_left());
graphics_box_state.set_content_width(path_bounding_box.width());
graphics_box_state.set_content_height(path_bounding_box.height());
graphics_box_state.set_has_definite_width(true);
graphics_box_state.set_has_definite_height(true);
graphics_box_state.set_computed_svg_path(move(path));
}
return TraversalDecision::Continue;
});
// 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<SVGBox>([&](SVGBox const& descendant) {
if (is_container_element(descendant)) {
Gfx::BoundingBox<CSSPixels> bounding_box;
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 TraversalDecision::Continue;
});
auto& box_state = m_state.get_mutable(descendant);
box_state.set_content_x(bounding_box.x());
box_state.set_content_y(bounding_box.y());
box_state.set_content_width(bounding_box.width());
box_state.set_content_height(bounding_box.height());
box_state.set_has_definite_width(true);
box_state.set_has_definite_height(true);
}
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;
});
}
}
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