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LibWeb: Implement font-size: math

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This is a MathML extension, basically a big hack to make parts of
equations smaller, such as sub/superscripts. The important thing is, it
works. :^)
This commit is contained in:
Sam Atkins 2023-09-07 17:39:07 +01:00 • committed by Sam Atkins
parent 6476dea898
commit f7209fb9d4
5 changed files with 104 additions and 12 deletions
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62
Userland/Libraries/LibWeb/CSS/StyleComputer.cpp
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@ -1907,7 +1907,7 @@ RefPtr<Gfx::Font const> StyleComputer::font_matching_algorithm(FontFaceKey const
return {};
}
RefPtr<Gfx::Font const> StyleComputer::compute_font_for_style_values(DOM::Element const* element, Optional<CSS::Selector::PseudoElement> pseudo_element, StyleValue const& font_family, StyleValue const& font_size, StyleValue const& font_style, StyleValue const& font_weight, StyleValue const& font_stretch) const
RefPtr<Gfx::Font const> StyleComputer::compute_font_for_style_values(DOM::Element const* element, Optional<CSS::Selector::PseudoElement> pseudo_element, StyleValue const& font_family, StyleValue const& font_size, StyleValue const& font_style, StyleValue const& font_weight, StyleValue const& font_stretch, int math_depth) const
{
auto* parent_element = element_to_inherit_style_from(element, pseudo_element);
@ -1972,16 +1972,58 @@ RefPtr<Gfx::Font const> StyleComputer::compute_font_for_style_values(DOM::Elemen
auto const identifier = static_cast<IdentifierStyleValue const&>(font_size).id();
// https://w3c.github.io/csswg-drafts/css-fonts/#valdef-font-size-relative-size
// TODO: If the parent element has a keyword font size in the absolute size keyword mapping table,
// larger may compute the font size to the next entry in the table,
// and smaller may compute the font size to the previous entry in the table.
if (identifier == CSS::ValueID::Smaller || identifier == CSS::ValueID::Larger) {
if (parent_element && parent_element->computed_css_values()) {
font_size_in_px = CSSPixels::nearest_value_for(parent_element->computed_css_values()->computed_font().pixel_metrics().size);
if (identifier == ValueID::Math) {
auto math_scaling_factor = [&]() {
// https://w3c.github.io/mathml-core/#the-math-script-level-property
// If the specified value font-size is math then the computed value of font-size is obtained by multiplying
// the inherited value of font-size by a nonzero scale factor calculated by the following procedure:
// 1. Let A be the inherited math-depth value, B the computed math-depth value, C be 0.71 and S be 1.0
int inherited_math_depth = parent_element && parent_element->computed_css_values()
? parent_element->computed_css_values()->math_depth()
: InitialValues::math_depth();
int computed_math_depth = math_depth;
auto size_ratio = 0.71;
auto scale = 1.0;
// 2. If A = B then return S.
bool invert_scale_factor = false;
if (inherited_math_depth == computed_math_depth) {
return scale;
}
// If B < A, swap A and B and set InvertScaleFactor to true.
else if (computed_math_depth < inherited_math_depth) {
AK::swap(inherited_math_depth, computed_math_depth);
invert_scale_factor = true;
}
// Otherwise B > A and set InvertScaleFactor to false.
else {
invert_scale_factor = false;
}
// 3. Let E be B - A > 0.
double e = (computed_math_depth - inherited_math_depth) > 0;
// FIXME: 4. If the inherited first available font has an OpenType MATH table:
// - If A ≤ 0 and B ≥ 2 then multiply S by scriptScriptPercentScaleDown and decrement E by 2.
// - Otherwise if A = 1 then multiply S by scriptScriptPercentScaleDown / scriptPercentScaleDown and decrement E by 1.
// - Otherwise if B = 1 then multiply S by scriptPercentScaleDown and decrement E by 1.
// 5. Multiply S by C^E.
scale *= AK::pow(size_ratio, e);
// 6. Return S if InvertScaleFactor is false and 1/S otherwise.
if (!invert_scale_factor)
return scale;
return 1.0 / scale;
};
font_size_in_px = parent_font_size().scale_by(math_scaling_factor());
} else {
// https://w3c.github.io/csswg-drafts/css-fonts/#valdef-font-size-relative-size
// TODO: If the parent element has a keyword font size in the absolute size keyword mapping table,
// larger may compute the font size to the next entry in the table,
// and smaller may compute the font size to the previous entry in the table.
if (identifier == CSS::ValueID::Smaller || identifier == CSS::ValueID::Larger) {
if (parent_element && parent_element->computed_css_values()) {
font_size_in_px = CSSPixels::nearest_value_for(parent_element->computed_css_values()->computed_font().pixel_metrics().size);
}
}
font_size_in_px *= get_absolute_size_mapping(identifier);
}
font_size_in_px *= get_absolute_size_mapping(identifier);
} else {
Length::ResolutionContext const length_resolution_context {
.viewport_rect = viewport_rect(),
@ -2126,7 +2168,7 @@ void StyleComputer::compute_font(StyleProperties& style, DOM::Element const* ele
auto font_weight = style.property(CSS::PropertyID::FontWeight);
auto font_stretch = style.property(CSS::PropertyID::FontStretch);
auto found_font = compute_font_for_style_values(element, pseudo_element, font_family, font_size, font_style, font_weight, font_stretch);
auto found_font = compute_font_for_style_values(element, pseudo_element, font_family, font_size, font_style, font_weight, font_stretch, style.math_depth());
style.set_property(CSS::PropertyID::FontSize, LengthStyleValue::create(CSS::Length::make_px(CSSPixels::nearest_value_for(found_font->pixel_size()))), nullptr);
style.set_property(CSS::PropertyID::FontWeight, NumberStyleValue::create(font_weight->to_font_weight()));