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[gpos] Share cursive attachment across glyph-ID widths #498

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Merged
behdad merged 1 commit into from
Oct 5, 2026
Merged

[gpos] Share cursive attachment across glyph-ID widths #498

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210 changes: 112 additions & 98 deletions harfrust/src/ot/gpos/cursive.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,7 @@ use crate::ot::apply::{Apply, SkippingIterator};
use crate::ot::gpos::attach_type;
use crate::ot::lookup_flags;
use crate::{Direction, GlyphPosition};
use read_fonts::tables::gpos::{CursivePosFormat1, CursivePosFormat2};
use read_fonts::tables::gpos::{AnchorTable, CursivePosFormat1, CursivePosFormat2};

macro_rules! impl_cursive_pos {
($format:ident) => {
Expand Down Expand Up @@ -44,103 +44,7 @@ macro_rules! impl_cursive_pos {
return None;
};

let (exit_x, exit_y) = ctx.layout.ot.resolve_anchor(&exit_prev);
let (entry_x, entry_y) = ctx.layout.ot.resolve_anchor(&entry_this);
let exit_x = ctx.scale_x(exit_x);
let exit_y = ctx.scale_y(exit_y);
let entry_x = ctx.scale_x(entry_x);
let entry_y = ctx.scale_y(entry_y);

let direction = ctx.buffer.direction;
let j = ctx.buffer.idx;
ctx.buffer.unsafe_to_break(Some(i), Some(j + 1));

let pos = &mut ctx.buffer.pos;
match direction {
Direction::LeftToRight => {
pos[i].x_advance = exit_x.saturating_add(pos[i].x_offset);
let d = entry_x.saturating_add(pos[j].x_offset);
pos[j].x_advance = pos[j].x_advance.saturating_sub(d);
pos[j].x_offset = pos[j].x_offset.saturating_sub(d);
}
Direction::RightToLeft => {
let d = exit_x.saturating_add(pos[i].x_offset);
pos[i].x_advance = pos[i].x_advance.saturating_sub(d);
pos[i].x_offset = pos[i].x_offset.saturating_sub(d);
pos[j].x_advance = entry_x.saturating_add(pos[j].x_offset);
}
Direction::TopToBottom => {
pos[i].y_advance = exit_y.saturating_add(pos[i].y_offset);
let d = entry_y.saturating_add(pos[j].y_offset);
pos[j].y_advance = pos[j].y_advance.saturating_sub(d);
pos[j].y_offset = pos[j].y_offset.saturating_sub(d);
}
Direction::BottomToTop => {
let d = exit_y.saturating_add(pos[i].y_offset);
pos[i].y_advance = pos[i].y_advance.saturating_sub(d);
pos[i].y_offset = pos[i].y_offset.saturating_sub(d);
pos[j].y_advance = entry_y;
}
Direction::Invalid => {}
}

// Cross-direction adjustment

// We attach child to parent (think graph theory and rooted trees whereas
// the root stays on baseline and each node aligns itself against its
// parent.
//
// Optimize things for the case of RightToLeft, as that's most common in
// Arabic.
let mut child = i;
let mut parent = j;
let mut x_offset = entry_x.saturating_sub(exit_x);
let mut y_offset = entry_y.saturating_sub(exit_y);

// Low bits are lookup flags, so we want to truncate.
if ctx.lookup_props as u16 & lookup_flags::RIGHT_TO_LEFT == 0 {
core::mem::swap(&mut child, &mut parent);
x_offset = x_offset.saturating_neg();
y_offset = y_offset.saturating_neg();
}

// If child was already connected to someone else, walk through its old
// chain and reverse the link direction, such that the whole tree of its
// previous connection now attaches to new parent. Watch out for case
// where new parent is on the path from old chain...
reverse_cursive_minor_offset(pos, child, direction, parent);

pos[child].set_attach_type(attach_type::CURSIVE);
let chain = parent as isize - child as isize;
pos[child].set_attach_chain(chain as i16);
// If the distance between the two glyphs does not fit in the i16 chain
// field it would be truncated to a bogus value; leave the glyph
// unattached instead of storing a poisoned chain. Matches HarfBuzz.
if isize::from(pos[child].attach_chain()) != chain {
pos[child].set_attach_chain(0);
}

ctx.buffer.scratch_flags |= HB_BUFFER_SCRATCH_FLAG_HAS_GPOS_ATTACHMENT;
if direction.is_horizontal() {
pos[child].y_offset = y_offset;
} else {
pos[child].x_offset = x_offset;
}

// If parent was attached to child, separate them.
// https://github.com/harfbuzz/harfbuzz/issues/2469
if pos[parent].attach_chain() == -pos[child].attach_chain() {
pos[parent].set_attach_chain(0);

if direction.is_horizontal() {
pos[parent].y_offset = 0;
} else {
pos[parent].x_offset = 0;
}
}

ctx.buffer.idx += 1;
Some(())
apply_cursive_attachment(ctx, i, &entry_this, &exit_prev)
}
}
};
Expand All @@ -149,6 +53,116 @@ macro_rules! impl_cursive_pos {
impl_cursive_pos!(CursivePosFormat1);
impl_cursive_pos!(CursivePosFormat2);

// Keep the format-independent attachment logic shared by both widths.
#[inline(never)]
fn apply_cursive_attachment(
ctx: &mut ApplyContext,
i: usize,
entry_anchor: &AnchorTable<'_>,
exit_anchor: &AnchorTable<'_>,
) -> Option<()> {
let (exit_x, exit_y) = ctx.layout.ot.resolve_anchor(exit_anchor);
let (entry_x, entry_y) = ctx.layout.ot.resolve_anchor(entry_anchor);
let exit_x = ctx.scale_x(exit_x);
let exit_y = ctx.scale_y(exit_y);
let entry_x = ctx.scale_x(entry_x);
let entry_y = ctx.scale_y(entry_y);

let direction = ctx.buffer.direction;
let j = ctx.buffer.idx;
ctx.buffer.unsafe_to_break(Some(i), Some(j + 1));

let pos = &mut ctx.buffer.pos;
match direction {
Direction::LeftToRight => {
pos[i].x_advance = exit_x.saturating_add(pos[i].x_offset);
let d = entry_x.saturating_add(pos[j].x_offset);
pos[j].x_advance = pos[j].x_advance.saturating_sub(d);
pos[j].x_offset = pos[j].x_offset.saturating_sub(d);
}
Direction::RightToLeft => {
let d = exit_x.saturating_add(pos[i].x_offset);
pos[i].x_advance = pos[i].x_advance.saturating_sub(d);
pos[i].x_offset = pos[i].x_offset.saturating_sub(d);
pos[j].x_advance = entry_x.saturating_add(pos[j].x_offset);
}
Direction::TopToBottom => {
pos[i].y_advance = exit_y.saturating_add(pos[i].y_offset);
let d = entry_y.saturating_add(pos[j].y_offset);
pos[j].y_advance = pos[j].y_advance.saturating_sub(d);
pos[j].y_offset = pos[j].y_offset.saturating_sub(d);
}
Direction::BottomToTop => {
let d = exit_y.saturating_add(pos[i].y_offset);
pos[i].y_advance = pos[i].y_advance.saturating_sub(d);
pos[i].y_offset = pos[i].y_offset.saturating_sub(d);
pos[j].y_advance = entry_y;
}
Direction::Invalid => {}
}

// Cross-direction adjustment

// We attach child to parent (think graph theory and rooted trees whereas
// the root stays on baseline and each node aligns itself against its
// parent.
//
// Optimize things for the case of RightToLeft, as that's most common in
// Arabic.
let mut child = i;
let mut parent = j;
let mut x_offset = entry_x.saturating_sub(exit_x);
let mut y_offset = entry_y.saturating_sub(exit_y);

// Low bits are lookup flags, so we want to truncate.
if ctx.lookup_props as u16 & lookup_flags::RIGHT_TO_LEFT == 0 {
core::mem::swap(&mut child, &mut parent);
x_offset = x_offset.saturating_neg();
y_offset = y_offset.saturating_neg();
}

// If child was already connected to someone else, walk through its old
// chain and reverse the link direction, such that the whole tree of its
// previous connection now attaches to new parent. Watch out for case
// where new parent is on the path from old chain...
reverse_cursive_minor_offset(pos, child, direction, parent);

let child_pos = &mut pos[child];
child_pos.set_attach_type(attach_type::CURSIVE);
let chain = parent as isize - child as isize;
child_pos.set_attach_chain(chain as i16);
// If the distance between the two glyphs does not fit in the i16 chain
// field it would be truncated to a bogus value; leave the glyph
// unattached instead of storing a poisoned chain. Matches HarfBuzz.
if isize::from(child_pos.attach_chain()) != chain {
child_pos.set_attach_chain(0);
}

ctx.buffer.scratch_flags |= HB_BUFFER_SCRATCH_FLAG_HAS_GPOS_ATTACHMENT;
if direction.is_horizontal() {
child_pos.y_offset = y_offset;
} else {
child_pos.x_offset = x_offset;
}
let child_chain = child_pos.attach_chain();

// If parent was attached to child, separate them.
// https://github.com/harfbuzz/harfbuzz/issues/2469
let parent_pos = &mut pos[parent];
if parent_pos.attach_chain() == -child_chain {
parent_pos.set_attach_chain(0);

if direction.is_horizontal() {
parent_pos.y_offset = 0;
} else {
parent_pos.x_offset = 0;
}
}

ctx.buffer.idx += 1;
Some(())
}

fn reverse_cursive_minor_offset(
pos: &mut [GlyphPosition],
i: usize,
Expand Down
61 changes: 37 additions & 24 deletions harfrust/src/ot/tests/extended.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -608,42 +608,55 @@ fn single_pos4_rejects_coverage_indices_outside_the_value_array() {
}

#[test]
fn cursive_pos2_attaches_wide_glyphs_in_all_directions() {
let subtable = [
fn cursive_pos_formats_attach_glyphs_in_all_directions() {
let narrow = [
0, 1, 0, 14, 0, 2, // Header and two records.
0, 0, 0, 22, // First glyph's exit anchor.
0, 28, 0, 0, // Second glyph's entry anchor.
0, 1, 0, 2, 0, 1, 0, 2, // Coverage.
0, 1, 0, 100, 0, 50, // Exit anchor.
0, 1, 0, 20, 0, 10, // Entry anchor.
];
let wide = [
0, 2, 0, 0, 0, 21, 0, 0, 2, // Header and two records.
0, 0, 0, 0, 0, 32, // First glyph's exit anchor.
0, 0, 38, 0, 0, 0, // Second glyph's entry anchor.
0, 3, 0, 0, 2, 1, 0, 0, 1, 0, 1, // Coverage.
0, 1, 0, 100, 0, 50, // Exit anchor.
0, 1, 0, 20, 0, 10, // Entry anchor.
];
for (direction, expected) in [
(Direction::LeftToRight, [[0, 0, 100, 0], [-20, 40, -20, 0]]),
(Direction::RightToLeft, [[-100, 0, -100, 0], [0, 40, 20, 0]]),
(Direction::TopToBottom, [[0, 0, 0, 50], [80, -10, 0, -10]]),
(Direction::BottomToTop, [[0, -50, 0, -50], [80, 0, 0, 10]]),
for (subtable, glyphs) in [
(narrow.as_slice(), [1, 2]),
(wide.as_slice(), [65536, 65537]),
] {
let output = apply_subtable_configured(3, false, &subtable, &[65536, 65537], |ctx| {
ctx.buffer.set_direction(direction);
});
for (pos, expected) in output.glyph_positions().iter().zip(expected) {
for (direction, expected) in [
(Direction::LeftToRight, [[0, 0, 100, 0], [-20, 40, -20, 0]]),
(Direction::RightToLeft, [[-100, 0, -100, 0], [0, 40, 20, 0]]),
(Direction::TopToBottom, [[0, 0, 0, 50], [80, -10, 0, -10]]),
(Direction::BottomToTop, [[0, -50, 0, -50], [80, 0, 0, 10]]),
] {
let output = apply_subtable_configured(3, false, subtable, &glyphs, |ctx| {
ctx.buffer.set_direction(direction);
});
for (pos, expected) in output.glyph_positions().iter().zip(expected) {
assert_eq!(
[pos.x_offset, pos.y_offset, pos.x_advance, pos.y_advance],
expected
);
}
assert_eq!(output.glyph_positions()[1].attach_chain(), -1);
assert_eq!(
[pos.x_offset, pos.y_offset, pos.x_advance, pos.y_advance],
expected
output.glyph_positions()[1].attach_type(),
gpos::attach_type::CURSIVE
);
}
assert_eq!(output.glyph_positions()[1].attach_chain(), -1);
assert_eq!(
output.glyph_positions()[1].attach_type(),
gpos::attach_type::CURSIVE
);
}

let output = apply_subtable_configured(3, false, &subtable, &[65536, 65537], |ctx| {
ctx.lookup_props |= u32::from(lookup_flags::RIGHT_TO_LEFT);
});
assert_eq!(output.glyph_positions()[0].attach_chain(), 1);
assert_eq!(output.glyph_positions()[0].y_offset, -40);
let output = apply_subtable_configured(3, false, subtable, &glyphs, |ctx| {
ctx.lookup_props |= u32::from(lookup_flags::RIGHT_TO_LEFT);
});
assert_eq!(output.glyph_positions()[0].attach_chain(), 1);
assert_eq!(output.glyph_positions()[0].y_offset, -40);
}
}

#[test]
Expand Down
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