//! Latin specific autohinting support.
use super::{
super::unscaled::UnscaledOutlineBuf,
cycling::{cycle_backward, cycle_forward},
metrics::{UnscaledBlue, UnscaledBlues, MAX_BLUES},
script::{blue_flags, ScriptClass},
};
use crate::{FontRef, MetadataProvider};
use raw::types::F2Dot14;
use raw::TableProvider;
impl UnscaledBlue {
fn is_latin_any_top(&self) -> bool {
self.flags & (blue_flags::LATIN_TOP | blue_flags::LATIN_SUB_TOP) != 0
}
}
impl UnscaledBlues {
/// Computes the set of blues for Latin style hinting.
///
/// See <https://gitlab.freedesktop.org/freetype/freetype/-/blob/57617782464411201ce7bbc93b086c1b4d7d84a5/src/autofit/aflatin.c#L314>
pub fn new_latin(font: &FontRef, coords: &[F2Dot14], script: &ScriptClass) -> Self {
const MAX_INLINE_POINTS: usize = 64;
const BLUE_STRING_MAX_LEN: usize = 51;
let mut blues = Self::new();
let mut outline_buf = UnscaledOutlineBuf::<MAX_INLINE_POINTS>::new();
let mut flats = [0; BLUE_STRING_MAX_LEN];
let mut rounds = [0; BLUE_STRING_MAX_LEN];
let glyphs = font.outline_glyphs();
let charmap = font.charmap();
let units_per_em = font
.head()
.map(|head| head.units_per_em())
.unwrap_or_default() as i32;
let flat_threshold = units_per_em / 14;
// Walk over each of the blue character sets for our script.
for (blue_chars, blue_flags) in script.blues {
let is_top_like =
(blue_flags & (blue_flags::LATIN_TOP | blue_flags::LATIN_SUB_TOP)) != 0;
let is_top = blue_flags & blue_flags::LATIN_TOP != 0;
let is_x_height = blue_flags & blue_flags::LATIN_X_HEIGHT != 0;
let is_neutral = blue_flags & blue_flags::LATIN_NEUTRAL != 0;
let is_long = blue_flags & blue_flags::LATIN_LONG != 0;
let mut ascender = i16::MIN;
let mut descender = i16::MAX;
let mut n_flats = 0;
let mut n_rounds = 0;
for ch in *blue_chars {
// TODO: do some shaping
let y_offset = 0;
let Some(gid) = charmap.map(*ch) else {
continue;
};
if gid.to_u32() == 0 {
continue;
}
let Some(glyph) = glyphs.get(gid) else {
continue;
};
outline_buf.clear();
if glyph.draw_unscaled(coords, None, &mut outline_buf).is_err() {
continue;
}
let outline = outline_buf.as_ref();
// Reject glyphs that don't produce any rendering
if outline.points.len() <= 2 {
continue;
}
let mut best_y: Option<i16> = None;
let mut best_y_extremum = if is_top { i32::MIN } else { i32::MAX };
let mut best_is_round = false;
// Find the extreme point depending on whether this is a top or
// bottom blue
let best_contour_and_point = if is_top_like {
outline.find_last_contour(|point| {
if best_y.is_none() || Some(point.y) > best_y {
best_y = Some(point.y);
ascender = ascender.max(point.y + y_offset);
true
} else {
descender = descender.min(point.y + y_offset);
false
}
})
} else {
outline.find_last_contour(|point| {
if best_y.is_none() || Some(point.y) < best_y {
best_y = Some(point.y);
descender = descender.min(point.y + y_offset);
true
} else {
ascender = ascender.max(point.y + y_offset);
false
}
})
};
let Some((best_contour_range, best_point_ix)) = best_contour_and_point else {
continue;
};
let best_contour = &outline.points[best_contour_range];
// If we have a contour and point then best_y is guaranteed to
// be Some
let mut best_y = best_y.unwrap() as i32;
let best_x = best_contour[best_point_ix].x as i32;
// Now determine whether the point belongs to a straight or
// round segment by examining the previous and next points.
let [mut on_point_first, mut on_point_last] =
if best_contour[best_point_ix].is_on_curve() {
[Some(best_point_ix); 2]
} else {
[None; 2]
};
let mut segment_first = best_point_ix;
let mut segment_last = best_point_ix;
// Look for the previous and next points on the contour that
// are not on the same Y coordinate, then threshold the
// "closeness"
for (ix, prev) in cycle_backward(best_contour, best_point_ix) {
let dist = (prev.y as i32 - best_y).abs();
// Allow a small distance or angle (20 == roughly 2.9 degrees)
if dist > 5 && ((prev.x as i32 - best_x).abs() <= (20 * dist)) {
break;
}
segment_first = ix;
if prev.is_on_curve() {
on_point_first = Some(ix);
if on_point_last.is_none() {
on_point_last = Some(ix);
}
}
}
let mut next_ix = 0;
for (ix, next) in cycle_forward(best_contour, best_point_ix) {
// Save next_ix which is used in "long" blue computation
// later
next_ix = ix;
let dist = (next.y as i32 - best_y).abs();
// Allow a small distance or angle (20 == roughly 2.9 degrees)
if dist > 5 && ((next.x as i32 - best_x).abs() <= (20 * dist)) {
break;
}
segment_last = ix;
if next.is_on_curve() {
on_point_last = Some(ix);
if on_point_first.is_none() {
on_point_first = Some(ix);
}
}
}
if is_long {
// Taken verbatim from FreeType:
//
// "If this flag is set, we have an additional constraint to
// get the blue zone distance: Find a segment of the topmost
// (or bottommost) contour that is longer than a heuristic
// threshold. This ensures that small bumps in the outline
// are ignored (for example, the `vertical serifs' found in
// many Hebrew glyph designs).
//
// If this segment is long enough, we are done. Otherwise,
// search the segment next to the extremum that is long
// enough, has the same direction, and a not too large
// vertical distance from the extremum. Note that the
// algorithm doesn't check whether the found segment is
// actually the one (vertically) nearest to the extremum.""
//
// See <https://gitlab.freedesktop.org/freetype/freetype/-/blob/57617782464411201ce7bbc93b086c1b4d7d84a5/src/autofit/aflatin.c#L641>
// heuristic threshold value
let length_threshold = units_per_em / 25;
let dist =
best_contour[segment_last].x as i32 - best_contour[segment_first].x as i32;
if dist < length_threshold
&& segment_last - segment_first + 2 <= best_contour.len()
{
// heuristic threshold value
let height_threshold = units_per_em / 4;
// find previous point with different x value
let mut prev_ix = best_point_ix;
for (ix, prev) in cycle_backward(best_contour, best_point_ix) {
if prev.x as i32 != best_x {
prev_ix = ix;
break;
}
}
// skip for degenerate case
if prev_ix == best_point_ix {
continue;
}
let is_ltr = (best_contour[prev_ix].x as i32) < best_x;
let mut first = segment_last;
let mut last = first;
let mut p_first = None;
let mut p_last = None;
let mut hit = false;
loop {
if !hit {
// no hit, adjust first point
first = last;
// also adjust first and last on curve point
if best_contour[first].is_on_curve() {
p_first = Some(first);
p_last = Some(first);
} else {
p_first = None;
p_last = None;
}
hit = true;
}
if last < best_contour.len() - 1 {
last += 1;
} else {
last = 0;
}
if (best_y - best_contour[first].y as i32).abs() > height_threshold {
// vertical distance too large
hit = false;
continue;
}
let dist =
(best_contour[last].y as i32 - best_contour[first].y as i32).abs();
if dist > 5
&& (best_contour[last].x as i32 - best_contour[first].x as i32)
.abs()
<= 20 * dist
{
hit = false;
continue;
}
if best_contour[last].is_on_curve() {
p_last = Some(last);
if p_first.is_none() {
p_first = Some(last);
}
}
let first_x = best_contour[first].x as i32;
let last_x = best_contour[last].x as i32;
let is_cur_ltr = first_x < last_x;
let dx = (last_x - first_x).abs();
if is_cur_ltr == is_ltr && dx >= length_threshold {
loop {
if last < best_contour.len() - 1 {
last += 1;
} else {
last = 0;
}
let dy = (best_contour[last].y as i32
- best_contour[first].y as i32)
.abs();
if dy > 5
&& (best_contour[next_ix].x as i32
- best_contour[first].x as i32)
.abs()
<= 20 * dist
{
if last > 0 {
last -= 1;
} else {
last = best_contour.len() - 1;
}
break;
}
p_last = Some(last);
if best_contour[last].is_on_curve() {
p_last = Some(last);
if p_first.is_none() {
p_first = Some(last);
}
}
if last == segment_first {
break;
}
}
best_y = best_contour[first].y as i32;
segment_first = first;
segment_last = last;
on_point_first = p_first;
on_point_last = p_last;
break;
}
if last == segment_first {
break;
}
}
}
}
best_y += y_offset as i32;
// Is the segment round?
// 1. horizontal distance between first and last oncurve point
// is larger than a heuristic flat threshold, then it's flat
// 2. either first or last point of segment is offcurve then
// it's round
let is_round = match (on_point_first, on_point_last) {
(Some(first), Some(last))
if (best_contour[last].x as i32 - best_contour[first].x as i32).abs()
> flat_threshold =>
{
false
}
_ => {
!best_contour[segment_first].is_on_curve()
|| !best_contour[segment_last].is_on_curve()
}
};
if is_round && is_neutral {
// Ignore round segments for neutral zone
continue;
}
// This seems to ignore LATIN_SUB_TOP?
if is_top {
if best_y > best_y_extremum {
best_y_extremum = best_y;
best_is_round = is_round;
}
} else if best_y < best_y_extremum {
best_y_extremum = best_y;
best_is_round = is_round;
}
if best_y_extremum != i32::MIN && best_y_extremum != i32::MAX {
if best_is_round {
rounds[n_rounds] = best_y_extremum;
n_rounds += 1;
} else {
flats[n_flats] = best_y_extremum;
n_flats += 1;
}
}
}
if n_flats == 0 && n_rounds == 0 {
continue;
}
rounds[..n_rounds].sort_unstable();
flats[..n_flats].sort_unstable();
let (mut blue_ref, mut blue_shoot) = if n_flats == 0 {
let val = rounds[n_rounds / 2];
(val, val)
} else if n_rounds == 0 {
let val = flats[n_flats / 2];
(val, val)
} else {
(flats[n_flats / 2], rounds[n_rounds / 2])
};
if blue_shoot != blue_ref {
let over_ref = blue_shoot > blue_ref;
if is_top_like ^ over_ref {
let val = (blue_shoot + blue_ref) / 2;
blue_ref = val;
blue_shoot = val;
}
}
let mut blue = UnscaledBlue {
position: blue_ref,
overshoot: blue_shoot,
ascender: ascender.into(),
descender: descender.into(),
flags: blue_flags
& (blue_flags::LATIN_TOP
| blue_flags::LATIN_SUB_TOP
| blue_flags::LATIN_NEUTRAL),
};
if is_x_height {
blue.flags |= blue_flags::LATIN_BLUE_ADJUSTMENT;
}
blues.push(blue);
}
// sort bottoms
let mut sorted_indices: [usize; MAX_BLUES] = core::array::from_fn(|ix| ix);
let blue_values = blues.as_mut_slice();
let len = blue_values.len();
if len == 0 {
return blues;
}
// sort from bottom to top
for i in 1..len {
for j in (1..=i).rev() {
let first = &blue_values[sorted_indices[j - 1]];
let second = &blue_values[sorted_indices[j]];
let a = if first.is_latin_any_top() {
first.position
} else {
first.overshoot
};
let b = if second.is_latin_any_top() {
second.position
} else {
second.overshoot
};
if b >= a {
break;
}
sorted_indices.swap(j, j - 1);
}
}
// and adjust tops
for i in 0..len - 1 {
let index1 = sorted_indices[i];
let index2 = sorted_indices[i + 1];
let first = &blue_values[index1];
let second = &blue_values[index2];
let a = if first.is_latin_any_top() {
first.overshoot
} else {
first.position
};
let b = if second.is_latin_any_top() {
second.overshoot
} else {
second.position
};
if a > b {
if first.is_latin_any_top() {
blue_values[index1].overshoot = b;
} else {
blue_values[index1].position = b;
}
}
}
blues
}
}
#[cfg(test)]
mod tests {
use super::{blue_flags, UnscaledBlue};
use raw::FontRef;
#[test]
fn latin_blues() {
let font = FontRef::new(font_test_data::NOTOSERIFHEBREW_AUTOHINT_METRICS).unwrap();
let script = &super::super::script::SCRIPT_CLASSES[super::ScriptClass::LATN];
let blues = super::UnscaledBlues::new_latin(&font, &[], script);
let values = blues.as_slice();
let expected = [
UnscaledBlue {
position: 714,
overshoot: 725,
ascender: 725,
descender: -230,
flags: blue_flags::LATIN_TOP,
},
UnscaledBlue {
position: 0,
overshoot: -10,
ascender: 725,
descender: -10,
flags: 0,
},
UnscaledBlue {
position: 760,
overshoot: 760,
ascender: 770,
descender: -240,
flags: blue_flags::LATIN_TOP,
},
UnscaledBlue {
position: 536,
overshoot: 546,
ascender: 546,
descender: -10,
flags: blue_flags::LATIN_TOP | blue_flags::LATIN_BLUE_ADJUSTMENT,
},
UnscaledBlue {
position: 0,
overshoot: -10,
ascender: 546,
descender: -10,
flags: 0,
},
UnscaledBlue {
position: -240,
overshoot: -240,
ascender: 760,
descender: -240,
flags: 0,
},
];
assert_eq!(values, &expected);
}
#[test]
fn latin_long_blues() {
let font = FontRef::new(font_test_data::NOTOSERIFHEBREW_AUTOHINT_METRICS).unwrap();
// Hebrew triggers "long" blue code path
let script = &super::super::script::SCRIPT_CLASSES[super::ScriptClass::HEBR];
let blues = super::UnscaledBlues::new_latin(&font, &[], script);
let values = blues.as_slice();
assert_eq!(values.len(), 3);
let expected = [
UnscaledBlue {
position: 592,
overshoot: 592,
ascender: 647,
descender: -240,
flags: blue_flags::LATIN_TOP,
},
UnscaledBlue {
position: 0,
overshoot: -9,
ascender: 647,
descender: -9,
flags: 0,
},
UnscaledBlue {
position: -240,
overshoot: -240,
ascender: 647,
descender: -240,
flags: 0,
},
];
assert_eq!(values, &expected);
}
}
Codebase Browser
chromium