ladybird/Libraries/LibWeb/CSS/Length.cpp
Callum Law 3b15c303f6 LibWeb: Use computed line-height for FontMetrics
We were already doing this within `compute_property_values` where
we resolved most relative lengths but the remainder was instead
incorrectly using the font's line-spacing
2025-09-23 15:57:32 +01:00

262 lines
10 KiB
C++

/*
* Copyright (c) 2020-2024, Andreas Kling <andreas@ladybird.org>
* Copyright (c) 2021, Tobias Christiansen <tobyase@serenityos.org>
* Copyright (c) 2022-2025, Sam Atkins <sam@ladybird.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/NonnullOwnPtr.h>
#include <AK/Variant.h>
#include <LibGfx/Font/Font.h>
#include <LibGfx/Rect.h>
#include <LibWeb/CSS/Length.h>
#include <LibWeb/CSS/Percentage.h>
#include <LibWeb/CSS/StyleComputer.h>
#include <LibWeb/DOM/Document.h>
#include <LibWeb/HTML/BrowsingContext.h>
#include <LibWeb/HTML/Window.h>
#include <LibWeb/Layout/Node.h>
namespace Web::CSS {
Length::FontMetrics::FontMetrics(CSSPixels font_size, Gfx::FontPixelMetrics const& pixel_metrics, CSSPixels line_height)
: font_size(font_size)
, x_height(pixel_metrics.x_height)
// FIXME: This is only approximately the cap height. The spec suggests measuring the "O" glyph:
// https://www.w3.org/TR/css-values-4/#cap
, cap_height(pixel_metrics.ascent)
, zero_advance(pixel_metrics.advance_of_ascii_zero)
, line_height(line_height)
{
}
Length::Length(double value, LengthUnit unit)
: m_unit(unit)
, m_value(value)
{
}
Length::~Length() = default;
Length Length::make_px(double value)
{
return Length(value, LengthUnit::Px);
}
Length Length::make_px(CSSPixels value)
{
return make_px(value.to_double());
}
Length Length::percentage_of(Percentage const& percentage) const
{
return Length { percentage.as_fraction() * raw_value(), m_unit };
}
CSSPixels Length::font_relative_length_to_px(Length::FontMetrics const& font_metrics, Length::FontMetrics const& root_font_metrics) const
{
switch (m_unit) {
case LengthUnit::Em:
return CSSPixels::nearest_value_for(m_value * font_metrics.font_size.to_double());
case LengthUnit::Rem:
return CSSPixels::nearest_value_for(m_value * root_font_metrics.font_size.to_double());
case LengthUnit::Ex:
return CSSPixels::nearest_value_for(m_value * font_metrics.x_height.to_double());
case LengthUnit::Rex:
return CSSPixels::nearest_value_for(m_value * root_font_metrics.x_height.to_double());
case LengthUnit::Cap:
return CSSPixels::nearest_value_for(m_value * font_metrics.cap_height.to_double());
case LengthUnit::Rcap:
return CSSPixels::nearest_value_for(m_value * root_font_metrics.cap_height.to_double());
case LengthUnit::Ch:
return CSSPixels::nearest_value_for(m_value * font_metrics.zero_advance.to_double());
case LengthUnit::Rch:
return CSSPixels::nearest_value_for(m_value * root_font_metrics.zero_advance.to_double());
case LengthUnit::Ic:
// FIXME: Use the "advance measure of the “水” (CJK water ideograph, U+6C34) glyph"
return CSSPixels::nearest_value_for(m_value * font_metrics.font_size.to_double());
case LengthUnit::Ric:
// FIXME: Use the "advance measure of the “水” (CJK water ideograph, U+6C34) glyph"
return CSSPixels::nearest_value_for(m_value * root_font_metrics.font_size.to_double());
case LengthUnit::Lh:
return CSSPixels::nearest_value_for(m_value * font_metrics.line_height.to_double());
case LengthUnit::Rlh:
return CSSPixels::nearest_value_for(m_value * root_font_metrics.line_height.to_double());
default:
VERIFY_NOT_REACHED();
}
}
CSSPixels Length::viewport_relative_length_to_px(CSSPixelRect const& viewport_rect) const
{
switch (m_unit) {
case LengthUnit::Vw:
case LengthUnit::Svw:
case LengthUnit::Lvw:
case LengthUnit::Dvw:
return viewport_rect.width() * (CSSPixels::nearest_value_for(m_value) / 100);
case LengthUnit::Vh:
case LengthUnit::Svh:
case LengthUnit::Lvh:
case LengthUnit::Dvh:
return viewport_rect.height() * (CSSPixels::nearest_value_for(m_value) / 100);
case LengthUnit::Vi:
case LengthUnit::Svi:
case LengthUnit::Lvi:
case LengthUnit::Dvi:
// FIXME: Select the width or height based on which is the inline axis.
return viewport_rect.width() * (CSSPixels::nearest_value_for(m_value) / 100);
case LengthUnit::Vb:
case LengthUnit::Svb:
case LengthUnit::Lvb:
case LengthUnit::Dvb:
// FIXME: Select the width or height based on which is the block axis.
return viewport_rect.height() * (CSSPixels::nearest_value_for(m_value) / 100);
case LengthUnit::Vmin:
case LengthUnit::Svmin:
case LengthUnit::Lvmin:
case LengthUnit::Dvmin:
return min(viewport_rect.width(), viewport_rect.height()) * (CSSPixels::nearest_value_for(m_value) / 100);
case LengthUnit::Vmax:
case LengthUnit::Svmax:
case LengthUnit::Lvmax:
case LengthUnit::Dvmax:
return max(viewport_rect.width(), viewport_rect.height()) * (CSSPixels::nearest_value_for(m_value) / 100);
default:
VERIFY_NOT_REACHED();
}
}
Length::ResolutionContext Length::ResolutionContext::for_element(DOM::AbstractElement const& element)
{
auto const* root_element = element.element().document().document_element();
VERIFY(element.computed_properties());
VERIFY(root_element);
VERIFY(root_element->computed_properties());
return Length::ResolutionContext {
.viewport_rect = element.element().navigable()->viewport_rect(),
.font_metrics = { element.computed_properties()->font_size(), element.computed_properties()->first_available_computed_font().pixel_metrics(), element.computed_properties()->line_height() },
.root_font_metrics = { root_element->computed_properties()->font_size(), root_element->computed_properties()->first_available_computed_font().pixel_metrics(), element.computed_properties()->line_height() }
};
}
Length::ResolutionContext Length::ResolutionContext::for_window(HTML::Window const& window)
{
auto const& initial_font = window.associated_document().style_computer().initial_font();
Gfx::FontPixelMetrics const& initial_font_metrics = initial_font.pixel_metrics();
Length::FontMetrics font_metrics { CSSPixels { initial_font.pixel_size() }, initial_font_metrics, InitialValues::line_height() };
return Length::ResolutionContext {
.viewport_rect = window.page().web_exposed_screen_area(),
.font_metrics = font_metrics,
.root_font_metrics = font_metrics,
};
}
Length::ResolutionContext Length::ResolutionContext::for_layout_node(Layout::Node const& node)
{
Layout::Node const* root_layout_node;
if (is<DOM::Document>(node.dom_node())) {
root_layout_node = &node;
} else {
auto const* root_element = node.document().document_element();
VERIFY(root_element);
VERIFY(root_element->layout_node());
root_layout_node = root_element->layout_node();
}
return Length::ResolutionContext {
.viewport_rect = node.navigable()->viewport_rect(),
.font_metrics = { node.computed_values().font_size(), node.first_available_font().pixel_metrics(), node.computed_values().line_height() },
.root_font_metrics = { root_layout_node->computed_values().font_size(), root_layout_node->first_available_font().pixel_metrics(), node.computed_values().line_height() },
};
}
CSSPixels Length::to_px(ResolutionContext const& context) const
{
return to_px(context.viewport_rect, context.font_metrics, context.root_font_metrics);
}
CSSPixels Length::to_px_slow_case(Layout::Node const& layout_node) const
{
if (!layout_node.document().browsing_context())
return 0;
if (is_font_relative()) {
auto* root_element = layout_node.document().document_element();
if (!root_element || !root_element->layout_node())
return 0;
FontMetrics font_metrics {
layout_node.computed_values().font_size(),
layout_node.first_available_font().pixel_metrics(),
layout_node.computed_values().line_height()
};
FontMetrics root_font_metrics {
root_element->layout_node()->computed_values().font_size(),
root_element->layout_node()->first_available_font().pixel_metrics(),
layout_node.computed_values().line_height()
};
return font_relative_length_to_px(font_metrics, root_font_metrics);
}
VERIFY(is_viewport_relative());
auto const& viewport_rect = layout_node.document().viewport_rect();
return viewport_relative_length_to_px(viewport_rect);
}
String Length::to_string(SerializationMode serialization_mode) const
{
// https://drafts.csswg.org/cssom/#serialize-a-css-value
// -> <length>
// The <number> component serialized as per <number> followed by the unit in its canonical form as defined in its
// respective specification.
// FIXME: Manually skip this for px so we avoid rounding errors in absolute_length_to_px.
// Maybe provide alternative functions that don't produce CSSPixels?
if (serialization_mode == SerializationMode::ResolvedValue && is_absolute() && m_unit != LengthUnit::Px) {
StringBuilder builder;
serialize_a_number(builder, absolute_length_to_px().to_double());
builder.append("px"sv);
return builder.to_string_without_validation();
}
StringBuilder builder;
serialize_a_number(builder, m_value);
builder.append(unit_name());
return builder.to_string_without_validation();
}
Optional<Length> Length::absolutize(CSSPixelRect const& viewport_rect, FontMetrics const& font_metrics, FontMetrics const& root_font_metrics) const
{
if (is_px())
return {};
if (is_absolute() || is_relative()) {
auto px = to_px(viewport_rect, font_metrics, root_font_metrics);
return CSS::Length::make_px(px);
}
return {};
}
Length Length::absolutized(CSSPixelRect const& viewport_rect, FontMetrics const& font_metrics, FontMetrics const& root_font_metrics) const
{
return absolutize(viewport_rect, font_metrics, root_font_metrics).value_or(*this);
}
Length Length::resolve_calculated(NonnullRefPtr<CalculatedStyleValue const> const& calculated, Layout::Node const& layout_node, Length const& reference_value)
{
CalculationResolutionContext context {
.percentage_basis = reference_value,
.length_resolution_context = ResolutionContext::for_layout_node(layout_node),
};
return calculated->resolve_length(context).value();
}
Length Length::resolve_calculated(NonnullRefPtr<CalculatedStyleValue const> const& calculated, Layout::Node const& layout_node, CSSPixels reference_value)
{
return resolve_calculated(calculated, layout_node, make_px(reference_value));
}
}