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//! Implementation of font shaping for Arabic scripts
//!
//! Code herein follows the specification at:
//! <https://github.com/n8willis/opentype-shaping-documents/blob/master/opentype-shaping-arabic-general.md>
use unicode_joining_type::{get_joining_type, JoiningType};
use crate::error::{ParseError, ShapingError};
use crate::gsub::{self, Feature, FeatureMask, GlyphData, GlyphOrigin, RawGlyph};
use crate::layout::{FeatureTableSubstitution, GDEFTable, LayoutCache, LayoutTable, GSUB};
use crate::tag;
use crate::unicode::mcc::{
modified_combining_class, sort_by_modified_combining_class, ModifiedCombiningClass,
};
#[derive(Clone)]
struct ArabicData {
joining_type: JoiningType,
feature_tag: u32,
}
impl GlyphData for ArabicData {
fn merge(data1: ArabicData, _data2: ArabicData) -> ArabicData {
// TODO hold off for future Unicode normalisation changes
data1
// Arabic glyphs are represented as `RawGlyph` structs with `ArabicData` for its `extra_data`.
type ArabicGlyph = RawGlyph<ArabicData>;
impl ArabicGlyph {
fn is_transparent(&self) -> bool {
self.extra_data.joining_type == JoiningType::Transparent || self.multi_subst_dup()
fn is_left_joining(&self) -> bool {
self.extra_data.joining_type == JoiningType::LeftJoining
|| self.extra_data.joining_type == JoiningType::DualJoining
|| self.extra_data.joining_type == JoiningType::JoinCausing
fn is_right_joining(&self) -> bool {
self.extra_data.joining_type == JoiningType::RightJoining
fn feature_tag(&self) -> u32 {
self.extra_data.feature_tag
fn set_feature_tag(&mut self, feature_tag: u32) {
self.extra_data.feature_tag = feature_tag
impl From<&RawGlyph<()>> for ArabicGlyph {
fn from(raw_glyph: &RawGlyph<()>) -> ArabicGlyph {
// Since there's no `Char` to work out the `ArabicGlyph`s joining type when the glyph's
// `glyph_origin` is `GlyphOrigin::Direct`, we fallback to `JoiningType::NonJoining` as
// the safest approach
let joining_type = match raw_glyph.glyph_origin {
GlyphOrigin::Char(c) => get_joining_type(c),
GlyphOrigin::Direct => JoiningType::NonJoining,
ArabicGlyph {
unicodes: raw_glyph.unicodes.clone(),
glyph_index: raw_glyph.glyph_index,
liga_component_pos: raw_glyph.liga_component_pos,
glyph_origin: raw_glyph.glyph_origin,
flags: raw_glyph.flags,
variation: raw_glyph.variation,
extra_data: ArabicData {
joining_type,
// For convenience, we loosely follow the spec (`2. Computing letter joining
// states`) here by initialising all `ArabicGlyph`s to `tag::ISOL`
feature_tag: tag::ISOL,
},
impl From<&ArabicGlyph> for RawGlyph<()> {
fn from(arabic_glyph: &ArabicGlyph) -> RawGlyph<()> {
RawGlyph {
unicodes: arabic_glyph.unicodes.clone(),
glyph_index: arabic_glyph.glyph_index,
liga_component_pos: arabic_glyph.liga_component_pos,
glyph_origin: arabic_glyph.glyph_origin,
flags: arabic_glyph.flags,
variation: arabic_glyph.variation,
extra_data: (),
pub fn gsub_apply_arabic(
gsub_cache: &LayoutCache<GSUB>,
gsub_table: &LayoutTable<GSUB>,
gdef_table: Option<&GDEFTable>,
script_tag: u32,
lang_tag: Option<u32>,
feature_variations: Option<&FeatureTableSubstitution<'_>>,
extra_features: FeatureMask,
raw_glyphs: &mut Vec<RawGlyph<()>>,
max_glyphs: usize,
) -> Result<(), ShapingError> {
match gsub_table.find_script(script_tag)? {
Some(s) => {
if s.find_langsys_or_default(lang_tag)?.is_none() {
return Ok(());
None => return Ok(()),
let arabic_glyphs = &mut raw_glyphs.iter().map(ArabicGlyph::from).collect();
// 1. Compound character composition and decomposition
apply_lookups(
Feature::CCMP.mask(),
gsub_cache,
gsub_table,
gdef_table,
script_tag,
lang_tag,
feature_variations,
arabic_glyphs,
max_glyphs,
|_, _| true,
)?;
// 2. Computing letter joining states
{
let mut previous_i = arabic_glyphs
.iter()
.position(|g| !g.is_transparent())
.unwrap_or(0);
for i in (previous_i + 1)..arabic_glyphs.len() {
if arabic_glyphs[i].is_transparent() {
continue;
if arabic_glyphs[previous_i].is_left_joining() && arabic_glyphs[i].is_right_joining() {
arabic_glyphs[i].set_feature_tag(tag::FINA);
match arabic_glyphs[previous_i].feature_tag() {
tag::ISOL => arabic_glyphs[previous_i].set_feature_tag(tag::INIT),
tag::FINA => arabic_glyphs[previous_i].set_feature_tag(tag::MEDI),
_ => {}
previous_i = i;
// 3. Applying the stch feature
//
// TODO hold off for future generalised solution (including the Syriac Abbreviation Mark)
// 4. Applying the language-form substitution features from GSUB
const LANGUAGE_FEATURES: &[(Feature, bool)] = &[
(Feature::LOCL, true),
(Feature::ISOL, false),
(Feature::FINA, false),
(Feature::MEDI, false),
(Feature::INIT, false),
(Feature::RLIG, true),
(Feature::RCLT, true),
(Feature::CALT, true),
];
for &(feature, is_global) in LANGUAGE_FEATURES {
feature.mask(),
|g, feature_tag| is_global || g.feature_tag() == feature_tag,
// 5. Applying the typographic-form substitution features from GSUB
let typographic_features = Feature::LIGA | Feature::MSET;
typographic_features | extra_features,
// 6. Mark reordering
// Handled in the text preprocessing stage.
*raw_glyphs = arabic_glyphs.iter().map(RawGlyph::from).collect();
Ok(())
fn apply_lookups(
feature_mask: FeatureMask,
arabic_glyphs: &mut Vec<ArabicGlyph>,
pred: impl Fn(&ArabicGlyph, u32) -> bool + Copy,
) -> Result<(), ParseError> {
let index = gsub::get_lookups_cache_index(
feature_mask,
let lookups = &gsub_cache.cached_lookups.lock().unwrap()[index];
for &(lookup_index, feature_tag) in lookups {
gsub::gsub_apply_lookup(
lookup_index,
feature_tag,
None,
0,
arabic_glyphs.len(),
|g| pred(g, feature_tag),
/// Reorder Arabic marks per AMTRA. See: <https://www.unicode.org/reports/tr53/>.
pub(super) fn reorder_marks(cs: &mut [char]) {
sort_by_modified_combining_class(cs);
for css in
cs.split_mut(|&c| modified_combining_class(c) == ModifiedCombiningClass::NotReordered)
reorder_marks_shadda(css);
reorder_marks_other_combining(css, ModifiedCombiningClass::Above);
reorder_marks_other_combining(css, ModifiedCombiningClass::Below);
fn reorder_marks_shadda(cs: &mut [char]) {
use std::cmp::Ordering;
// 2a. Move any Shadda characters to the beginning of S, where S is a max
// length substring of non-starter characters.
fn comparator(c1: &char, _c2: &char) -> Ordering {
if modified_combining_class(*c1) == ModifiedCombiningClass::CCC33 {
Ordering::Less
} else {
Ordering::Equal
cs.sort_by(comparator)
fn reorder_marks_other_combining(cs: &mut [char], mcc: ModifiedCombiningClass) {
debug_assert!(mcc == ModifiedCombiningClass::Below || mcc == ModifiedCombiningClass::Above);
// Get the start index of a possible sequence of characters with canonical
// combining class equal to `mcc`. (Assumes that `glyphs` is normalised to
// NFD.)
let first = cs.iter().position(|&c| modified_combining_class(c) == mcc);
if let Some(first) = first {
// 2b/2c. If the sequence of characters _begins_ with any MCM characters,
// move the sequence of such characters to the beginning of S.
let count = cs[first..]
.take_while(|&&c| is_modifier_combining_mark(c))
.count();
cs[..(first + count)].rotate_right(count);
fn is_modifier_combining_mark(ch: char) -> bool {
// https://www.unicode.org/reports/tr53/tr53-6.html#MCM
match ch {
| '\u{0654}' // ARABIC HAMZA ABOVE
| '\u{0655}' // ARABIC HAMZA BELOW
| '\u{0658}' // ARABIC MARK NOON GHUNNA
| '\u{06DC}' // ARABIC SMALL HIGH SEEN
| '\u{06E3}' // ARABIC SMALL LOW SEEN
| '\u{06E7}' // ARABIC SMALL HIGH YEH
| '\u{06E8}' // ARABIC SMALL HIGH NOON
| '\u{08CA}' // ARABIC SMALL HIGH FARSI YEH
| '\u{08CB}' // ARABIC SMALL HIGH YEH BARREE WITH TWO DOTS BELOW
| '\u{08CD}' // ARABIC SMALL HIGH ZAH
| '\u{08CE}' // ARABIC LARGE ROUND DOT ABOVE
| '\u{08CF}' // ARABIC LARGE ROUND DOT BELOW
| '\u{08D3}' // ARABIC SMALL LOW WAW
| '\u{08F3}' => true, // ARABIC SMALL HIGH WAW
_ => false,
#[cfg(test)]
mod tests {
use super::*;
// https://www.unicode.org/reports/tr53/#Demonstrating_AMTRA.
mod reorder_marks {
#[test]
fn test_artificial() {
let cs = vec![
'\u{0618}', '\u{0619}', '\u{064E}', '\u{064F}', '\u{0654}', '\u{0658}', '\u{0653}',
'\u{0654}', '\u{0651}', '\u{0656}', '\u{0651}', '\u{065C}', '\u{0655}', '\u{0650}',
let cs_exp = vec![
'\u{0654}', '\u{0658}', '\u{0651}', '\u{0651}', '\u{0618}', '\u{064E}', '\u{0619}',
'\u{064F}', '\u{0650}', '\u{0656}', '\u{065C}', '\u{0655}', '\u{0653}', '\u{0654}',
test_reorder_marks(&cs, &cs_exp);
// Variant of `test_artificial` where U+0656 is replaced with U+0655
// to test the reordering of MCM characters for the ccc = 220 group.
fn test_artificial_custom() {
'\u{0654}', '\u{0651}', '\u{0655}', '\u{0651}', '\u{065C}', '\u{0655}', '\u{0650}',
'\u{0655}', '\u{0654}', '\u{0658}', '\u{0651}', '\u{0651}', '\u{0618}', '\u{064E}',
'\u{0619}', '\u{064F}', '\u{0650}', '\u{065C}', '\u{0655}', '\u{0653}', '\u{0654}',
fn test_example1() {
let cs1 = vec!['\u{0627}', '\u{064F}', '\u{0654}'];
let cs1_exp = vec!['\u{0627}', '\u{0654}', '\u{064F}'];
test_reorder_marks(&cs1, &cs1_exp);
let cs2 = vec!['\u{0627}', '\u{064F}', '\u{034F}', '\u{0654}'];
test_reorder_marks(&cs2, &cs2);
let cs3 = vec!['\u{0649}', '\u{0650}', '\u{0655}'];
let cs3_exp = vec!['\u{0649}', '\u{0655}', '\u{0650}'];
test_reorder_marks(&cs3, &cs3_exp);
let cs4 = vec!['\u{0649}', '\u{0650}', '\u{034F}', '\u{0655}'];
test_reorder_marks(&cs4, &cs4);
fn test_example2a() {
let cs = vec!['\u{0635}', '\u{06DC}', '\u{0652}'];
test_reorder_marks(&cs, &cs);
fn test_example2b() {
let cs1 = vec!['\u{0647}', '\u{0652}', '\u{06DC}'];
let cs1_exp = vec!['\u{0647}', '\u{06DC}', '\u{0652}'];
let cs2 = vec!['\u{0647}', '\u{0652}', '\u{034F}', '\u{06DC}'];
fn test_example3() {
let cs1 = vec!['\u{0640}', '\u{0650}', '\u{0651}', '\u{06E7}'];
// The expected output in https://www.unicode.org/reports/tr53/#Example3
// [U+0640, U+0650, U+06E7, U+0651]
// is incorrect, in that it fails to account for U+0651 Shadda moving to
// the front of U+0650 Kasra, per step 2a of AMTRA.
// U+06E7 Small High Yeh should then move to the front of Shadda per step
// 2b, resulting in:
let cs1_exp = vec!['\u{0640}', '\u{06E7}', '\u{0651}', '\u{0650}'];
let cs2 = vec!['\u{0640}', '\u{0650}', '\u{0651}', '\u{034F}', '\u{06E7}'];
// As above, Shadda should move to the front of Kasra, so the expected
// output in https://www.unicode.org/reports/tr53/#Example3
// [U+0640, U+0650, U+0651, U+034F, U+06E7]
// (i.e. no changes) is also incorrect.
let cs2_exp = vec!['\u{0640}', '\u{0651}', '\u{0650}', '\u{034F}', '\u{06E7}'];
test_reorder_marks(&cs2, &cs2_exp);
fn test_example4a() {
let cs = vec!['\u{0640}', '\u{0652}', '\u{034F}', '\u{06E8}'];
fn test_example4b() {
let cs1 = vec!['\u{06C6}', '\u{064F}', '\u{06E8}'];
let cs1_exp = vec!['\u{06C6}', '\u{06E8}', '\u{064F}'];
let cs2 = vec!['\u{06C6}', '\u{064F}', '\u{034F}', '\u{06E8}'];
fn test_reorder_marks(cs: &Vec<char>, cs_exp: &Vec<char>) {
let mut cs_act = cs.clone();
reorder_marks(&mut cs_act);
assert_eq!(cs_exp, &cs_act);