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b55023fad3
Previously we would resolve font features (https://drafts.csswg.org/css-fonts-4/#feature-variation-precedence) per element, while this works for the current subset of the font feature resolution algorithm that we support, some as yet unimplemented parts require us to know whether we are resolving against a CSS @font-face rule, and if so which one (e.g. applying descriptors from the @font-face rule, deciding which @font-feature-values rules to apply, etc). To achieve this we store the data required to resolve font features in a struct and pass that to `FontComputer` which resolves the font features and stores them with the computed `Font`. We no longer need to invalidate the font shaping cache when features change since the features are defined per font (and therefore won't ever change).
280 lines
12 KiB
C++
280 lines
12 KiB
C++
/*
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* Copyright (c) 2026, Callum Law <callumlaw1709@outlook.com>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include "FontFeatureData.h"
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#include <AK/HashMap.h>
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namespace Web::CSS {
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Gfx::ShapeFeatures FontFeatureData::to_shape_features() const
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{
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HashMap<StringView, u8> merged_features;
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auto font_variant_features = [&]() {
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HashMap<StringView, u8> features;
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// 6.4 https://drafts.csswg.org/css-fonts/#font-variant-ligatures-prop
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auto disable_all_ligatures = [&]() {
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features.set("liga"sv, 0);
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features.set("clig"sv, 0);
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features.set("dlig"sv, 0);
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features.set("hlig"sv, 0);
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features.set("calt"sv, 0);
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};
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if (font_variant_ligatures.has_value()) {
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auto ligature = font_variant_ligatures.value();
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if (ligature.none) {
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// Specifies that all types of ligatures and contextual forms covered by this property are explicitly disabled.
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disable_all_ligatures();
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} else {
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switch (ligature.common) {
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case Gfx::FontVariantLigatures::Common::Common:
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// Enables display of common ligatures (OpenType features: liga, clig).
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features.set("liga"sv, 1);
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features.set("clig"sv, 1);
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break;
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case Gfx::FontVariantLigatures::Common::NoCommon:
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// Disables display of common ligatures (OpenType features: liga, clig).
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features.set("liga"sv, 0);
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features.set("clig"sv, 0);
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break;
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case Gfx::FontVariantLigatures::Common::Unset:
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break;
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}
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switch (ligature.discretionary) {
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case Gfx::FontVariantLigatures::Discretionary::Discretionary:
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// Enables display of discretionary ligatures (OpenType feature: dlig).
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features.set("dlig"sv, 1);
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break;
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case Gfx::FontVariantLigatures::Discretionary::NoDiscretionary:
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// Disables display of discretionary ligatures (OpenType feature: dlig).
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features.set("dlig"sv, 0);
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break;
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case Gfx::FontVariantLigatures::Discretionary::Unset:
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break;
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}
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switch (ligature.historical) {
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case Gfx::FontVariantLigatures::Historical::Historical:
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// Enables display of historical ligatures (OpenType feature: hlig).
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features.set("hlig"sv, 1);
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break;
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case Gfx::FontVariantLigatures::Historical::NoHistorical:
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// Disables display of historical ligatures (OpenType feature: hlig).
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features.set("hlig"sv, 0);
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break;
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case Gfx::FontVariantLigatures::Historical::Unset:
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break;
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}
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switch (ligature.contextual) {
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case Gfx::FontVariantLigatures::Contextual::Contextual:
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// Enables display of contextual ligatures (OpenType feature: calt).
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features.set("calt"sv, 1);
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break;
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case Gfx::FontVariantLigatures::Contextual::NoContextual:
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// Disables display of contextual ligatures (OpenType feature: calt).
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features.set("calt"sv, 0);
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break;
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case Gfx::FontVariantLigatures::Contextual::Unset:
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break;
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}
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}
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} else if (text_rendering == TextRendering::Optimizespeed) {
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// AD-HOC: Disable ligatures if font-variant-ligatures is set to normal and text rendering is set to optimize speed.
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disable_all_ligatures();
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} else {
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// A value of normal specifies that common default features are enabled, as described in detail in the next section.
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features.set("liga"sv, 1);
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features.set("clig"sv, 1);
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}
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// 6.5 https://drafts.csswg.org/css-fonts/#font-variant-position-prop
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switch (font_variant_position) {
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case FontVariantPosition::Normal:
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// None of the features listed below are enabled.
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break;
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case FontVariantPosition::Sub:
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// Enables display of subscripts (OpenType feature: subs).
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features.set("subs"sv, 1);
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break;
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case FontVariantPosition::Super:
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// Enables display of superscripts (OpenType feature: sups).
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features.set("sups"sv, 1);
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break;
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default:
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break;
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}
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// 6.6 https://drafts.csswg.org/css-fonts/#font-variant-caps-prop
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switch (font_variant_caps) {
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case FontVariantCaps::Normal:
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// None of the features listed below are enabled.
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break;
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case FontVariantCaps::SmallCaps:
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// Enables display of small capitals (OpenType feature: smcp). Small-caps glyphs typically use the form of uppercase letters but are reduced to the size of lowercase letters.
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features.set("smcp"sv, 1);
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break;
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case FontVariantCaps::AllSmallCaps:
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// Enables display of small capitals for both upper and lowercase letters (OpenType features: c2sc, smcp).
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features.set("c2sc"sv, 1);
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features.set("smcp"sv, 1);
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break;
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case FontVariantCaps::PetiteCaps:
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// Enables display of petite capitals (OpenType feature: pcap).
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features.set("pcap"sv, 1);
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break;
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case FontVariantCaps::AllPetiteCaps:
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// Enables display of petite capitals for both upper and lowercase letters (OpenType features: c2pc, pcap).
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features.set("c2pc"sv, 1);
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features.set("pcap"sv, 1);
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break;
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case FontVariantCaps::Unicase:
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// Enables display of mixture of small capitals for uppercase letters with normal lowercase letters (OpenType feature: unic).
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features.set("unic"sv, 1);
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break;
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case FontVariantCaps::TitlingCaps:
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// Enables display of titling capitals (OpenType feature: titl).
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features.set("titl"sv, 1);
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break;
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default:
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break;
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}
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// 6.7 https://drafts.csswg.org/css-fonts/#font-variant-numeric-prop
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if (font_variant_numeric.has_value()) {
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auto numeric = font_variant_numeric.value();
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if (numeric.figure == Gfx::FontVariantNumeric::Figure::Oldstyle) {
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// Enables display of old-style numerals (OpenType feature: onum).
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features.set("onum"sv, 1);
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} else if (numeric.figure == Gfx::FontVariantNumeric::Figure::Lining) {
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// Enables display of lining numerals (OpenType feature: lnum).
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features.set("lnum"sv, 1);
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}
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if (numeric.spacing == Gfx::FontVariantNumeric::Spacing::Proportional) {
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// Enables display of proportional numerals (OpenType feature: pnum).
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features.set("pnum"sv, 1);
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} else if (numeric.spacing == Gfx::FontVariantNumeric::Spacing::Tabular) {
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// Enables display of tabular numerals (OpenType feature: tnum).
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features.set("tnum"sv, 1);
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}
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if (numeric.fraction == Gfx::FontVariantNumeric::Fraction::Diagonal) {
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// Enables display of diagonal fractions (OpenType feature: frac).
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features.set("frac"sv, 1);
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} else if (numeric.fraction == Gfx::FontVariantNumeric::Fraction::Stacked) {
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// Enables display of stacked fractions (OpenType feature: afrc).
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features.set("afrc"sv, 1);
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features.set("afrc"sv, 1);
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}
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if (numeric.ordinal) {
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// Enables display of letter forms used with ordinal numbers (OpenType feature: ordn).
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features.set("ordn"sv, 1);
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}
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if (numeric.slashed_zero) {
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// Enables display of slashed zeros (OpenType feature: zero).
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features.set("zero"sv, 1);
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}
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}
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// 6.10 https://drafts.csswg.org/css-fonts/#font-variant-east-asian-prop
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if (font_variant_east_asian.has_value()) {
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auto east_asian = font_variant_east_asian.value();
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switch (east_asian.variant) {
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case Gfx::FontVariantEastAsian::Variant::Jis78:
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// Enables display of JIS78 forms (OpenType feature: jp78).
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features.set("jp78"sv, 1);
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break;
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case Gfx::FontVariantEastAsian::Variant::Jis83:
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// Enables display of JIS83 forms (OpenType feature: jp83).
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features.set("jp83"sv, 1);
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break;
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case Gfx::FontVariantEastAsian::Variant::Jis90:
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// Enables display of JIS90 forms (OpenType feature: jp90).
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features.set("jp90"sv, 1);
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break;
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case Gfx::FontVariantEastAsian::Variant::Jis04:
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// Enables display of JIS04 forms (OpenType feature: jp04).
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features.set("jp04"sv, 1);
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break;
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case Gfx::FontVariantEastAsian::Variant::Simplified:
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// Enables display of simplified forms (OpenType feature: smpl).
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features.set("smpl"sv, 1);
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break;
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case Gfx::FontVariantEastAsian::Variant::Traditional:
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// Enables display of traditional forms (OpenType feature: trad).
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features.set("trad"sv, 1);
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break;
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default:
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break;
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}
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switch (east_asian.width) {
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case Gfx::FontVariantEastAsian::Width::FullWidth:
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// Enables display of full-width forms (OpenType feature: fwid).
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features.set("fwid"sv, 1);
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break;
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case Gfx::FontVariantEastAsian::Width::Proportional:
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// Enables display of proportional-width forms (OpenType feature: pwid).
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features.set("pwid"sv, 1);
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break;
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default:
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break;
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}
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if (east_asian.ruby) {
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// Enables display of ruby forms (OpenType feature: ruby).
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features.set("ruby"sv, 1);
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}
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}
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// FIXME: vkrn should be enabled for vertical text.
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switch (font_kerning) {
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case FontKerning::Auto:
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// AD-HOC: Disable kerning if font-kerning is set to normal and text rendering is set to optimize speed.
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features.set("kern"sv, text_rendering != TextRendering::Optimizespeed ? 1 : 0);
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break;
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case FontKerning::Normal:
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features.set("kern"sv, 1);
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break;
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case FontKerning::None:
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features.set("kern"sv, 0);
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break;
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default:
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break;
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}
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return features;
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};
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// https://www.w3.org/TR/css-fonts-3/#feature-precedence
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// FIXME: 1. Font features enabled by default, including features required for a given script.
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// FIXME: 2. If the font is defined via an @font-face rule, the font features implied by the font-feature-settings descriptor in the @font-face rule.
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// 3. Font features implied by the value of the ‘font-variant’ property, the related ‘font-variant’ subproperties and any other CSS property that uses OpenType features (e.g. the ‘font-kerning’ property).
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merged_features.update(font_variant_features());
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// FIXME: 4. Feature settings determined by properties other than ‘font-variant’ or ‘font-feature-settings’. For example, setting a non-default value for the ‘letter-spacing’ property disables common ligatures.
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// 5. Font features implied by the value of ‘font-feature-settings’ property.
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for (auto const& [key, value] : font_feature_settings)
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merged_features.set(key.bytes_as_string_view(), value);
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Gfx::ShapeFeatures shape_features;
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shape_features.ensure_capacity(merged_features.size());
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for (auto& it : merged_features)
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shape_features.unchecked_append({ { it.key[0], it.key[1], it.key[2], it.key[3] }, static_cast<u32>(it.value) });
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return shape_features;
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}
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}
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