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[skrifa] autohint: CJK edge hinting (#1138)
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Completes the CJK hinting algorithm
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@dfrg
dfrg authored Sep 7, 2024
1 parent f2735a4 commit 007d558
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Showing 7 changed files with 736 additions and 256 deletions.
187 changes: 178 additions & 9 deletions skrifa/src/outline/autohint/hint.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -20,29 +20,49 @@ use super::{
axis::{Axis, Dimension},
metrics::{fixed_div, fixed_mul, Scale},
outline::{Outline, Point},
style::ScriptGroup,
};
use core::cmp::Ordering;

/// Align all points of an edge to the same coordinate value.
///
/// See <https://gitlab.freedesktop.org/freetype/freetype/-/blob/57617782464411201ce7bbc93b086c1b4d7d84a5/src/autofit/afhints.c#L1324>
pub(crate) fn align_edge_points(outline: &mut Outline, axis: &Axis) -> Option<()> {
pub(crate) fn align_edge_points(
outline: &mut Outline,
axis: &Axis,
group: ScriptGroup,
scale: &Scale,
) -> Option<()> {
let edges = axis.edges.as_slice();
let segments = axis.segments.as_slice();
let points = outline.points.as_mut_slice();
// Snapping is configurable for CJK
// See <https://gitlab.freedesktop.org/freetype/freetype/-/blob/57617782464411201ce7bbc93b086c1b4d7d84a5/src/autofit/afcjk.c#L2195>
let snap = group == ScriptGroup::Default
|| ((axis.dim == Axis::HORIZONTAL && scale.flags & Scale::HORIZONTAL_SNAP != 0)
|| (axis.dim == Axis::VERTICAL && scale.flags & Scale::VERTICAL_SNAP != 0));
for segment in segments {
let Some(edge) = segment.edge(edges) else {
continue;
};
let delta = edge.pos - edge.opos;
let mut point_ix = segment.first();
let last_ix = segment.last();
loop {
let point = points.get_mut(point_ix)?;
if axis.dim == Axis::HORIZONTAL {
point.x = edge.pos;
if snap {
point.x = edge.pos;
} else {
point.x += delta;
}
point.flags.set_marker(PointMarker::TOUCHED_X);
} else {
point.y = edge.pos;
if snap {
point.y = edge.pos;
} else {
point.y += delta;
}
point.flags.set_marker(PointMarker::TOUCHED_Y);
}
if point_ix == last_ix {
Expand All @@ -67,7 +87,8 @@ pub(crate) fn align_strong_points(outline: &mut Outline, axis: &mut Axis) -> Opt
} else {
PointMarker::TOUCHED_Y
};
'points: for point in &mut outline.points {
let points = outline.points.as_mut_slice();
'points: for point in points {
// Skip points that are already touched; do weak interpolation in the
// next pass
if point
Expand Down Expand Up @@ -326,15 +347,17 @@ mod tests {
};

#[test]
fn hinted_coords_and_metrics() {
fn hinted_coords_and_metrics_default() {
let font = FontRef::new(font_test_data::NOTOSERIFHEBREW_AUTOHINT_METRICS).unwrap();
let (outline, metrics) = hint_latin_outline(
let (outline, metrics) = hint_outline(
&font,
16.0,
Default::default(),
GlyphId::new(9),
&style::STYLE_CLASSES[style::StyleClass::HEBR],
);
// Expected values were painfully extracted from FreeType with some
// printf debugging
#[rustfmt::skip]
let expected_coords = [
(133, -256),
Expand Down Expand Up @@ -388,12 +411,158 @@ mod tests {
assert_eq!(metrics, expected_metrics);
}

#[test]
fn hinted_coords_and_metrics_cjk() {
let font = FontRef::new(font_test_data::NOTOSERIFTC_AUTOHINT_METRICS).unwrap();
let (outline, metrics) = hint_outline(
&font,
16.0,
Default::default(),
GlyphId::new(9),
&style::STYLE_CLASSES[style::StyleClass::HANI],
);
// Expected values were painfully extracted from FreeType with some
// printf debugging
let expected_coords = [
(279, 768),
(568, 768),
(618, 829),
(618, 829),
(634, 812),
(657, 788),
(685, 758),
(695, 746),
(692, 720),
(667, 720),
(288, 720),
(704, 704),
(786, 694),
(785, 685),
(777, 672),
(767, 670),
(767, 163),
(767, 159),
(750, 148),
(728, 142),
(716, 142),
(704, 142),
(402, 767),
(473, 767),
(473, 740),
(450, 598),
(338, 357),
(236, 258),
(220, 270),
(274, 340),
(345, 499),
(390, 675),
(344, 440),
(398, 425),
(464, 384),
(496, 343),
(501, 307),
(486, 284),
(458, 281),
(441, 291),
(434, 314),
(398, 366),
(354, 416),
(334, 433),
(832, 841),
(934, 830),
(932, 819),
(914, 804),
(896, 802),
(896, 30),
(896, 5),
(885, -35),
(848, -60),
(809, -65),
(807, -51),
(794, -27),
(781, -19),
(767, -11),
(715, 0),
(673, 5),
(673, 21),
(673, 21),
(707, 18),
(756, 15),
(799, 13),
(807, 13),
(821, 13),
(832, 23),
(832, 35),
(407, 624),
(594, 624),
(594, 546),
(396, 546),
(569, 576),
(558, 576),
(599, 614),
(677, 559),
(671, 552),
(654, 547),
(636, 545),
(622, 458),
(572, 288),
(488, 130),
(357, -5),
(259, -60),
(246, -45),
(327, 9),
(440, 150),
(516, 311),
(558, 486),
(128, 542),
(158, 581),
(226, 576),
(223, 562),
(207, 543),
(193, 539),
(193, -44),
(193, -46),
(175, -56),
(152, -64),
(141, -64),
(128, -64),
(195, 850),
(300, 820),
(295, 799),
(259, 799),
(234, 712),
(163, 543),
(80, 395),
(33, 338),
(19, 347),
(54, 410),
(120, 575),
(176, 759),
];
let coords = outline
.points
.iter()
.map(|point| (point.x, point.y))
.collect::<Vec<_>>();
assert_eq!(coords, expected_coords);
let expected_metrics = latin::HintedMetrics {
x_scale: 67109,
edge_metrics: Some(latin::EdgeMetrics {
left_opos: 141,
left_pos: 128,
right_opos: 933,
right_pos: 896,
}),
};
assert_eq!(metrics, expected_metrics);
}

/// Empty glyphs (like spaces) have no edges and therefore no edge
/// metrics
#[test]
fn missing_edge_metrics() {
let font = FontRef::new(font_test_data::CUBIC_GLYF).unwrap();
let (_outline, metrics) = hint_latin_outline(
let (_outline, metrics) = hint_outline(
&font,
16.0,
Default::default(),
Expand All @@ -413,7 +582,7 @@ mod tests {
#[test]
fn skia_ahem_test_case() {
let font = FontRef::new(font_test_data::AHEM).unwrap();
let outline = hint_latin_outline(
let outline = hint_outline(
&font,
24.0,
Default::default(),
Expand All @@ -440,7 +609,7 @@ mod tests {
assert_eq!(float_coords, expected_float_coords);
}

fn hint_latin_outline(
fn hint_outline(
font: &FontRef,
size: f32,
coords: &[F2Dot14],
Expand Down
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