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OneCAD/crates/sketch/src/text.rs
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Rust
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//! Sketch text: glyph outlines of a font as lines, conics and cubic splines, so text closes
//! into profiles that can be extruded. TrueType quadratic Béziers are conics with rho = 0.5;
//! OpenType (CFF) cubic Béziers are cubic control splines, both exact. A glyph's counters (the
//! holes of A, B, 8…) are loops inside its outline; profile detection makes them holes.
//!
//! The default font is embedded (Liberation Sans, SIL OFL 1.1; see `assets/fonts/liberation-sans/OFL.txt` and
//! ATTRIBUTION.md); [`crate::fonts`] finds others by file path or installed family name.
use serde::{Deserialize, Serialize};
use solidcraft_geom::Vec2;
use crate::fonts::font_data_styled;
use crate::link::{LinkGeom, LinkKind, LinkSource, MAX_LINK_ENTITIES};
use crate::model::{Result, Sketch, SketchError};
/// Most characters in one text.
pub const MAX_TEXT_CHARS: usize = 1000;
struct Outline {
out: Vec<LinkGeom>,
start: Vec2,
cur: Vec2,
map: Box<dyn Fn(f32, f32) -> Vec2>,
}
impl Outline {
fn line(&mut self, to: Vec2) {
if self.cur.dist(to) > 1e-9 {
self.out.push(LinkGeom::Line(self.cur, to));
}
self.cur = to;
}
fn quad(&mut self, apex: Vec2, to: Vec2) {
let (a, b) = (self.cur, to);
let chord = b - a;
let off = chord.cross(apex - a).abs() / chord.len().max(1e-12);
if off < 1e-6 || a.dist(b) < 1e-9 {
self.line(to);
return;
}
self.out.push(LinkGeom::Conic { a, apex, b, rho: 0.5 });
self.cur = to;
}
fn cubic(&mut self, c1: Vec2, c2: Vec2, to: Vec2) {
let (a, b) = (self.cur, to);
let chord = b - a;
let l = chord.len().max(1e-12);
let off = (chord.cross(c1 - a).abs() / l).max(chord.cross(c2 - a).abs() / l);
// Straight (controls on the chord, between its ends): a line.
let between = |c: Vec2| (c - a).dot(chord) >= -1e-9 && (c - b).dot(chord) <= 1e-9;
if a.dist(b) < 1e-9 || (off < 1e-6 && between(c1) && between(c2)) {
self.line(to);
return;
}
self.out.push(LinkGeom::Spline { pts: vec![a, c1, c2, b], control: true, degree: 3, periodic: false });
self.cur = to;
}
}
impl ttf_parser::OutlineBuilder for Outline {
fn move_to(&mut self, x: f32, y: f32) {
let p = (self.map)(x, y);
self.start = p;
self.cur = p;
}
fn line_to(&mut self, x: f32, y: f32) {
let p = (self.map)(x, y);
self.line(p);
}
fn quad_to(&mut self, x1: f32, y1: f32, x: f32, y: f32) {
let (c, p) = ((self.map)(x1, y1), (self.map)(x, y));
self.quad(c, p);
}
fn curve_to(&mut self, x1: f32, y1: f32, x2: f32, y2: f32, x: f32, y: f32) {
let (c1, c2, p) = ((self.map)(x1, y1), (self.map)(x2, y2), (self.map)(x, y));
self.cubic(c1, c2, p);
}
fn close(&mut self) {
let s = self.start;
self.line(s);
}
}
/// Where each line of a text sits against its anchor (`at`, or a point of its path).
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum TextAlign {
/// The line starts at the anchor.
#[default]
Left,
/// The line is centred on it.
Center,
/// The line ends at it.
Right,
}
impl TextAlign {
fn is_left(&self) -> bool {
*self == TextAlign::Left
}
}
/// How a text is set: the style of its font, where its lines sit, the space between its letters
/// and lines, and the sketch curve its baseline follows (instead of the straight line from `at`).
#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
pub struct TextStyle {
#[serde(default, skip_serializing_if = "is_false")]
pub bold: bool,
#[serde(default, skip_serializing_if = "is_false")]
pub italic: bool,
#[serde(default, skip_serializing_if = "TextAlign::is_left")]
pub align: TextAlign,
/// Extra space between letters (mm; negative brings them closer).
#[serde(default, skip_serializing_if = "is_zero")]
pub letter_spacing: f64,
/// The distance between lines as a multiple of the font's own.
#[serde(default = "one", skip_serializing_if = "is_one")]
pub line_spacing: f64,
/// The id of a curve of the same sketch the baseline follows (`at` and the angle then do not
/// place the text).
#[serde(default, skip_serializing_if = "Option::is_none")]
pub path: Option<String>,
/// Along the path the other way round, so the text sits on its other side.
#[serde(default, skip_serializing_if = "is_false")]
pub reverse: bool,
}
impl Default for TextStyle {
fn default() -> Self {
TextStyle { bold: false, italic: false, align: TextAlign::Left, letter_spacing: 0.0, line_spacing: 1.0, path: None, reverse: false }
}
}
impl TextStyle {
/// Nothing but the defaults (what a text saved before styles had).
pub fn is_plain(&self) -> bool {
*self == TextStyle::default()
}
}
fn is_false(b: &bool) -> bool {
!*b
}
fn is_zero(x: &f64) -> bool {
*x == 0.0
}
fn one() -> f64 {
1.0
}
fn is_one(x: &f64) -> bool {
*x == 1.0
}
/// How far a slanted (made-up italic) glyph leans: 12 degrees.
const SLANT_DEG: f64 = 12.0;
/// Largest letter spacing (mm either way) and line spacing factor accepted.
const MAX_LETTER_SPACING: f64 = 1e5;
const LINE_SPACING_RANGE: (f64, f64) = (0.05, 100.0);
/// Outline geometry of `text` in the built-in font (see [`text_geometry_in`]).
pub fn text_geometry(text: &str, at: Vec2, height: f64, angle: f64) -> Result<Vec<LinkGeom>> {
text_geometry_in(None, text, at, height, angle)
}
/// Outline geometry of `text` in `font` (None: the built-in font; else a font file path or an
/// installed family name, see [`crate::fonts::font_data`]) with its baseline starting at `at`,
/// capital height `height` (mm), rotated by `angle` (radians) about `at`. Lines break at `\n`.
pub fn text_geometry_in(font: Option<&str>, text: &str, at: Vec2, height: f64, angle: f64) -> Result<Vec<LinkGeom>> {
text_geometry_styled(font, text, at, height, angle, &TextStyle::default(), None)
}
/// Outline geometry of `text` set in `style` (see [`text_geometry_in`]). With `path` (the
/// points of the curve [`TextStyle::path`] names) the baseline follows it: each letter stands on
/// the curve, turned with it, and the lines after the first run below it.
pub fn text_geometry_styled(
font: Option<&str>,
text: &str,
at: Vec2,
height: f64,
angle: f64,
style: &TextStyle,
path: Option<&[Vec2]>,
) -> Result<Vec<LinkGeom>> {
if text.chars().count() > MAX_TEXT_CHARS {
return Err(SketchError::TooLarge);
}
if !(height.is_finite() && height > 1e-6 && height < 1e6 && angle.is_finite() && at.is_finite()) {
return Err(SketchError::Invalid("text height must be positive".into()));
}
if !(style.letter_spacing.is_finite() && style.letter_spacing.abs() <= MAX_LETTER_SPACING) {
return Err(SketchError::Invalid("the letter spacing must be a finite length".into()));
}
if !(style.line_spacing.is_finite() && (LINE_SPACING_RANGE.0..=LINE_SPACING_RANGE.1).contains(&style.line_spacing)) {
return Err(SketchError::Invalid(format!(
"the line spacing must be between {} and {} times the font's",
LINE_SPACING_RANGE.0, LINE_SPACING_RANGE.1
)));
}
let (data, slant) = font_data_styled(font, style.bold, style.italic)?;
let face = ttf_parser::Face::parse(data.bytes(), data.index).map_err(|e| SketchError::Invalid(format!("font: {e}")))?;
let k = height / cap_height(&face);
let line_gap = f64::from(face.ascender()) - f64::from(face.descender()) + f64::from(face.line_gap());
let line_gap = if line_gap > 0.0 { line_gap * k } else { height * 1.5 } * style.line_spacing;
let shear = if slant { SLANT_DEG.to_radians().tan() } else { 0.0 };
// Each line's glyphs (glyph, where its origin is along the line, its advance) and width.
let lines: Vec<(Vec<(ttf_parser::GlyphId, f64, f64)>, f64)> = text
.split('\n')
.map(|line| {
let mut pen = 0.0f64;
let mut glyphs = Vec::new();
for ch in line.chars() {
let Some(gid) = face.glyph_index(ch).or_else(|| face.glyph_index('?')) else { continue };
let advance = f64::from(face.glyph_hor_advance(gid).unwrap_or(0)) * k;
glyphs.push((gid, pen, advance));
pen += advance + style.letter_spacing;
}
let width = glyphs.last().map(|(_, x, advance)| x + advance).unwrap_or(0.0);
(glyphs, width)
})
.collect();
let along = path.map(|pts| Path::new(pts, style.reverse)).transpose()?;
let anchor = along.as_ref().map(|p| p.anchor(style.align)).unwrap_or(0.0);
let (sin, cos) = angle.sin_cos();
let mut out = Vec::new();
for (row, (glyphs, width)) in lines.iter().enumerate() {
let base_y = -(row as f64) * line_gap;
let start = match style.align {
TextAlign::Left => 0.0,
TextAlign::Center => -width / 2.0,
TextAlign::Right => -width,
};
for &(gid, x, advance) in glyphs {
// The glyph's frame: its origin on the baseline and the way the baseline runs.
let (origin, dir) = match &along {
None => {
let dir = Vec2::new(cos, sin);
(at + dir * (start + x) + Vec2::new(-sin, cos) * base_y, dir)
}
Some(p) => {
let (mid, dir) = p.frame(anchor + start + x + advance / 2.0, advance);
(mid - dir * (advance / 2.0) + Vec2::new(-dir.y, dir.x) * base_y, dir)
}
};
let up = Vec2::new(-dir.y, dir.x);
let map = Box::new(move |gx: f32, gy: f32| {
let (gx, gy) = (f64::from(gx) * k, f64::from(gy) * k);
origin + dir * (gx + gy * shear) + up * gy
});
let mut ob = Outline { out: Vec::new(), start: origin, cur: origin, map };
let _ = face.outline_glyph(gid, &mut ob);
out.extend(ob.out);
// A font can give a glyph any number of points: stop where the link would be refused anyway.
if out.len() > MAX_LINK_ENTITIES {
return Err(SketchError::TooLarge);
}
}
}
if out.iter().any(|g| !geom_finite(g)) {
return Err(SketchError::Invalid("the text does not fit its path".into()));
}
Ok(out)
}
fn geom_finite(g: &LinkGeom) -> bool {
match g {
LinkGeom::Line(a, b) => a.is_finite() && b.is_finite(),
LinkGeom::Conic { a, apex, b, rho } => a.is_finite() && apex.is_finite() && b.is_finite() && rho.is_finite(),
LinkGeom::Spline { pts, .. } => pts.iter().all(|p| p.is_finite()),
_ => true,
}
}
/// A curve a text follows, as points with the distance along it to each: oriented so the text
/// reads left to right (an open curve runs rightwards, a closed one clockwise, the text on its
/// outside) unless reversed.
struct Path {
pts: Vec<Vec2>,
along: Vec<f64>,
closed: bool,
}
impl Path {
fn new(points: &[Vec2], reverse: bool) -> Result<Path> {
let mut pts: Vec<Vec2> = Vec::with_capacity(points.len());
for p in points {
if !p.is_finite() {
return Err(SketchError::Invalid("the text's path is not a finite curve".into()));
}
if pts.last().is_none_or(|q: &Vec2| q.dist(*p) > 1e-9) {
pts.push(*p);
}
}
let (Some(first), Some(last)) = (pts.first().copied(), pts.last().copied()) else {
return Err(SketchError::Invalid("the text's path has no length".into()));
};
let length: f64 = pts.iter().zip(pts.iter().skip(1)).map(|(a, b)| a.dist(*b)).sum();
if pts.len() < 2 || length < 1e-9 {
return Err(SketchError::Invalid("the text's path has no length".into()));
}
let closed = first.dist(last) <= 1e-9 * length.max(1.0);
let readable = if closed {
// Clockwise: the text stands on the outside.
let area: f64 = pts.iter().zip(pts.iter().skip(1)).map(|(a, b)| a.cross(*b)).sum::<f64>() + last.cross(first);
area <= 0.0
} else {
last.x >= first.x - 1e-9 * length
};
if readable == reverse {
pts.reverse();
}
let mut along = Vec::with_capacity(pts.len());
let mut total = 0.0;
for (i, p) in pts.iter().enumerate() {
if let Some(prev) = i.checked_sub(1).and_then(|j| pts.get(j)) {
total += prev.dist(*p);
}
along.push(total);
}
Ok(Path { pts, along, closed })
}
fn length(&self) -> f64 {
self.along.last().copied().unwrap_or(0.0)
}
/// Where the lines are aligned to: an open curve's start, middle or end; on a closed curve
/// its top, whatever the alignment.
fn anchor(&self, align: TextAlign) -> f64 {
if self.closed {
return self.pts.iter().zip(&self.along).max_by(|(p, _), (q, _)| p.y.total_cmp(&q.y)).map(|(_, s)| *s).unwrap_or(0.0);
}
match align {
TextAlign::Left => 0.0,
TextAlign::Center => self.length() / 2.0,
TextAlign::Right => self.length(),
}
}
/// The point at distance `s` along the curve (around a closed one; past the ends of an open
/// one, straight on).
fn point(&self, s: f64) -> Vec2 {
let length = self.length();
let s = if self.closed { s.rem_euclid(length) } else { s };
let (first, last) = (self.pts.first().copied().unwrap_or_default(), self.pts.last().copied().unwrap_or_default());
if !self.closed && s <= 0.0 {
let d = self.pts.get(1).and_then(|q| (*q - first).normalized()).unwrap_or(Vec2::X);
return first + d * s;
}
if !self.closed && s >= length {
let n = self.pts.len();
let d = n.checked_sub(2).and_then(|i| self.pts.get(i)).and_then(|q| (last - *q).normalized()).unwrap_or(Vec2::X);
return last + d * (s - length);
}
let i = self.along.partition_point(|a| *a < s).clamp(1, self.pts.len().saturating_sub(1).max(1));
match (self.pts.get(i - 1), self.pts.get(i), self.along.get(i - 1), self.along.get(i)) {
(Some(a), Some(b), Some(sa), Some(sb)) if sb > sa => *a + (*b - *a) * ((s - sa) / (sb - sa)),
(Some(a), ..) => *a,
_ => first,
}
}
/// The point at `s` and the way the curve runs there, over a glyph `width` wide (the chord
/// across it, so a glyph sits evenly on a bend).
fn frame(&self, s: f64, width: f64) -> (Vec2, Vec2) {
let h = (width / 2.0).max(self.length() * 1e-4).max(1e-9);
let dir = (self.point(s + h) - self.point(s - h)).normalized().unwrap_or(Vec2::X);
(self.point(s), dir)
}
}
impl Sketch {
/// The outline geometry of a text source of this sketch: its path, when it has one, is a
/// curve of this sketch as it is now.
pub fn text_source_geometry(&self, src: &LinkSource) -> Result<Vec<LinkGeom>> {
let LinkSource::Text { text, at, height, angle, font, style } = src else {
return Err(SketchError::Invalid("not a text".into()));
};
let path = match &style.path {
None => None,
Some(id) => {
let ci = self.curve_index(id).ok_or_else(|| SketchError::Invalid(format!("the text's path `{id}` is not a curve of this sketch")))?;
let of_text =
self.curves.get(ci).and_then(|c| c.link.as_deref()).and_then(|l| self.link(l)).is_some_and(|l| l.kind == LinkKind::Text);
if of_text {
return Err(SketchError::Invalid("a text cannot follow the outline of a text".into()));
}
Some(self.polyline(ci))
}
};
text_geometry_styled(font.as_deref(), text, *at, *height, *angle, style, path.as_deref())
}
}
/// The font's capital height in font units: from its OS/2 table, else the top of its `H`, else
/// 70 % of the em.
fn cap_height(face: &ttf_parser::Face) -> f64 {
face.capital_height()
.map(f64::from)
.filter(|c| *c > 0.0)
.or_else(|| face.glyph_index('H').and_then(|g| face.glyph_bounding_box(g)).map(|b| f64::from(b.y_max)).filter(|c| *c > 0.0))
.unwrap_or(f64::from(face.units_per_em().max(1)) * 0.7)
}
#[cfg(test)]
#[path = "text_style_tests.rs"]
mod style_tests;
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn letters_have_closed_outlines_at_the_cap_height() {
let g = text_geometry("HO", Vec2::new(5.0, 0.0), 10.0, 0.0).unwrap();
assert!(!g.is_empty());
let ys: Vec<f64> = g
.iter()
.flat_map(|x| match *x {
LinkGeom::Line(a, b) => vec![a.y, b.y],
LinkGeom::Conic { a, b, .. } => vec![a.y, b.y],
_ => vec![],
})
.collect();
let top = ys.iter().cloned().fold(f64::MIN, f64::max);
assert!((top - 10.0).abs() < 0.3, "{top}");
assert!(g.iter().any(|x| matches!(x, LinkGeom::Conic { .. })), "O has curves");
assert!(text_geometry("x", Vec2::ZERO, -1.0, 0.0).is_err());
assert!(text_geometry(&"x".repeat(2000), Vec2::ZERO, 1.0, 0.0).is_err());
// Empty text makes nothing (not an error here; the command rejects it).
assert!(text_geometry("", Vec2::ZERO, 1.0, 0.0).unwrap().is_empty());
}
#[test]
fn a_font_file_gives_the_same_outlines_and_unknown_fonts_are_errors() {
let path = std::path::Path::new(env!("CARGO_MANIFEST_DIR")).join("../../assets/fonts/liberation-sans/LiberationSans-Regular.ttf");
let by_file = text_geometry_in(Some(&path.to_string_lossy()), "A7_L", Vec2::ZERO, 8.0, 0.0).unwrap();
assert_eq!(by_file, text_geometry("A7_L", Vec2::ZERO, 8.0, 0.0).unwrap());
let e = text_geometry_in(Some("No Such Family 12345"), "A", Vec2::ZERO, 8.0, 0.0).unwrap_err().to_string();
assert!(e.contains("unknown font"), "{e}");
}
#[test]
fn cubic_outlines_stay_exact_splines() {
let mut ob = Outline { out: Vec::new(), start: Vec2::ZERO, cur: Vec2::ZERO, map: Box::new(|x, y| Vec2::new(f64::from(x), f64::from(y))) };
ttf_parser::OutlineBuilder::move_to(&mut ob, 0.0, 0.0);
ttf_parser::OutlineBuilder::curve_to(&mut ob, 0.0, 10.0, 10.0, 10.0, 10.0, 0.0);
// A cubic with its controls on the chord is a line.
ttf_parser::OutlineBuilder::curve_to(&mut ob, 7.0, 0.0, 3.0, 0.0, 0.0, 0.0);
assert_eq!(ob.out.len(), 2);
assert!(matches!(&ob.out[0], LinkGeom::Spline { pts, control: true, degree: 3, .. } if pts.len() == 4));
assert!(matches!(ob.out[1], LinkGeom::Line(..)));
}
}
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