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[skrifa] autohint: CJK edge hinting #1138

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merged 5 commits into from
Sep 7, 2024
Merged

[skrifa] autohint: CJK edge hinting #1138

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9f8731b
[skrifa] autohint: CJK edges
dfrg Sep 5, 2024
03dfbe7
[skrifa] autohint: CJK edge hinting
dfrg Sep 6, 2024
c7eb6fe
Merge branch 'main' into autohint-cjk-edge-hinting
dfrg Sep 7, 2024
f5ceca1
review feedback
dfrg Sep 7, 2024
1431652
Merge branch 'main' into autohint-cjk-edge-hinting
dfrg Sep 7, 2024
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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 = [
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might be useful to just note where these came from..

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Noted that these are generated with some lovely printf debugging in FreeType

(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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