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effectcraft/crates/svg/src/pathdata.rs

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//! SVG path data (SVG 1.1 §8.3 / SVG 2 §9.3): every command, implicit repeats, relative
//! coordinates, smooth curves and elliptical arcs (converted to cubics through kurbo's `SvgArc`).
//! Parsing stops at the first error, keeping what was read (as the specification asks).
use kurbo::{BezPath, Point, SvgArc, Vec2};
/// Tokenizer over numbers and command letters.
struct Lex<'a> {
b: &'a [u8],
i: usize,
}
impl Lex<'_> {
fn skip_sep(&mut self) {
while self.i < self.b.len() && (self.b[self.i].is_ascii_whitespace() || self.b[self.i] == b',') {
self.i += 1;
}
}
fn command(&mut self) -> Option<u8> {
self.skip_sep();
let c = *self.b.get(self.i)?;
if c.is_ascii_alphabetic() && c != b'e' && c != b'E' {
self.i += 1;
Some(c)
} else {
None
}
}
fn at_number(&mut self) -> bool {
self.skip_sep();
self.b.get(self.i).is_some_and(|c| c.is_ascii_digit() || matches!(c, b'-' | b'+' | b'.'))
}
fn number(&mut self) -> Option<f64> {
self.skip_sep();
let start = self.i;
let b = self.b;
let mut i = self.i;
if i < b.len() && matches!(b[i], b'-' | b'+') {
i += 1;
}
let mut digits = false;
while i < b.len() && b[i].is_ascii_digit() {
i += 1;
digits = true;
}
if i < b.len() && b[i] == b'.' {
i += 1;
while i < b.len() && b[i].is_ascii_digit() {
i += 1;
digits = true;
}
}
if !digits {
return None;
}
if i < b.len() && matches!(b[i], b'e' | b'E') {
let mut j = i + 1;
if j < b.len() && matches!(b[j], b'-' | b'+') {
j += 1;
}
if j < b.len() && b[j].is_ascii_digit() {
while j < b.len() && b[j].is_ascii_digit() {
j += 1;
}
i = j;
}
}
self.i = i;
std::str::from_utf8(&b[start..i]).ok()?.parse().ok()
}
/// Arc flags may be written without separators ("a1 1 0 00 1 1").
fn flag(&mut self) -> Option<bool> {
self.skip_sep();
let c = *self.b.get(self.i)?;
self.i += 1;
match c {
b'0' => Some(false),
b'1' => Some(true),
_ => None,
}
}
}
/// All numbers in a list (`points`, `viewBox`, transform arguments).
pub fn numbers(s: &str) -> Vec<f64> {
let mut l = Lex { b: s.as_bytes(), i: 0 };
let mut v = vec![];
while l.at_number() {
match l.number() {
Some(x) => v.push(x),
None => break,
}
}
v
}
/// Parse path data into a kurbo path.
pub fn parse_path_data(d: &str) -> BezPath {
let mut l = Lex { b: d.as_bytes(), i: 0 };
let mut p = BezPath::new();
let mut cur = Point::ZERO;
let mut start = Point::ZERO;
// Last control point of the previous C/S (cubic) or Q/T (quad) command.
let mut last_cubic: Option<Point> = None;
let mut last_quad: Option<Point> = None;
let mut cmd: Option<u8> = None;
let mut open = false;
loop {
let c = match l.command() {
Some(c) => c,
None => match cmd {
// Implicit repeat (a moveto repeats as lineto). Z takes no numbers, so a number
// after it is an error: repeating Z would loop forever without consuming input.
Some(c) if l.at_number() && !c.eq_ignore_ascii_case(&b'z') => match c {
b'M' => b'L',
b'm' => b'l',
other => other,
},
_ => break,
},
};
let rel = c.is_ascii_lowercase();
let base = if rel { cur.to_vec2() } else { Vec2::ZERO };
let pt = |l: &mut Lex| -> Option<Point> { Some(Point::new(l.number()?, l.number()?) + base) };
let ok = (|| -> Option<()> {
match c.to_ascii_uppercase() {
b'M' => {
cur = pt(&mut l)?;
p.move_to(cur);
start = cur;
open = true;
last_cubic = None;
last_quad = None;
}
b'Z' => {
if open {
p.close_path();
}
cur = start;
last_cubic = None;
last_quad = None;
}
_ if !open => {
// A segment without a preceding moveto starts at the current point.
p.move_to(cur);
open = true;
return segment(&mut l, c, base, &mut p, &mut cur, &mut last_cubic, &mut last_quad);
}
_ => return segment(&mut l, c, base, &mut p, &mut cur, &mut last_cubic, &mut last_quad),
}
Some(())
})();
if ok.is_none() {
break;
}
cmd = Some(c);
if c.eq_ignore_ascii_case(&b'z') {
// After Z a new segment starts from the subpath start (an unused move is dropped
// below).
p.move_to(start);
open = true;
}
}
strip_trailing_moves(p)
}
fn segment(l: &mut Lex, c: u8, base: Vec2, p: &mut BezPath, cur: &mut Point, last_cubic: &mut Option<Point>, last_quad: &mut Option<Point>) -> Option<()> {
let num = |l: &mut Lex| l.number();
let pt = |l: &mut Lex| -> Option<Point> { Some(Point::new(l.number()?, l.number()?) + base) };
match c.to_ascii_uppercase() {
b'L' => {
*cur = pt(l)?;
p.line_to(*cur);
*last_cubic = None;
*last_quad = None;
}
b'H' => {
let x = num(l)? + base.x;
*cur = Point::new(x, cur.y);
p.line_to(*cur);
*last_cubic = None;
*last_quad = None;
}
b'V' => {
let y = num(l)? + base.y;
*cur = Point::new(cur.x, y);
p.line_to(*cur);
*last_cubic = None;
*last_quad = None;
}
b'C' => {
let (c1, c2, e) = (pt(l)?, pt(l)?, pt(l)?);
p.curve_to(c1, c2, e);
*last_cubic = Some(c2);
*last_quad = None;
*cur = e;
}
b'S' => {
let c1 = last_cubic.map_or(*cur, |c| *cur + (*cur - c));
let (c2, e) = (pt(l)?, pt(l)?);
p.curve_to(c1, c2, e);
*last_cubic = Some(c2);
*last_quad = None;
*cur = e;
}
b'Q' => {
let (q, e) = (pt(l)?, pt(l)?);
p.quad_to(q, e);
*last_quad = Some(q);
*last_cubic = None;
*cur = e;
}
b'T' => {
let q = last_quad.map_or(*cur, |c| *cur + (*cur - c));
let e = pt(l)?;
p.quad_to(q, e);
*last_quad = Some(q);
*last_cubic = None;
*cur = e;
}
b'A' => {
let rx = num(l)?.abs();
let ry = num(l)?.abs();
let rot = num(l)?;
let large = l.flag()?;
let sweep = l.flag()?;
let e = pt(l)?;
let arc = SvgArc { from: *cur, to: e, radii: Vec2::new(rx, ry), x_rotation: rot.to_radians(), large_arc: large, sweep };
match kurbo::Arc::from_svg_arc(&arc) {
Some(a) => a.to_cubic_beziers(0.1, |c1, c2, end| p.curve_to(c1, c2, end)),
None => p.line_to(e),
}
*cur = e;
*last_cubic = None;
*last_quad = None;
}
_ => return None,
}
Some(())
}
/// Drop move-tos that start no segment (from closepath bookkeeping).
fn strip_trailing_moves(p: BezPath) -> BezPath {
use kurbo::PathEl;
let els = p.elements();
let mut out = BezPath::new();
for (i, e) in els.iter().enumerate() {
if let PathEl::MoveTo(_) = e {
let next_is_seg = els.get(i + 1).is_some_and(|n| !matches!(n, PathEl::MoveTo(_)));
if !next_is_seg {
continue;
}
}
out.push(*e);
}
out
}
#[cfg(test)]
mod tests {
use super::*;
use kurbo::PathEl;
#[test]
fn commands() {
let p = parse_path_data("M10,10 L20,10 h10 v10 H10 z m5 5 l1-1.5.5.5e1 C 0 0 1 1 2 2 s3 3 4 4 Q1 1 2 2 t3 3 A5 5 0 0 1 20 20 a5 5 0 1010 0");
let els = p.elements();
assert_eq!(els[0], PathEl::MoveTo(Point::new(10.0, 10.0)));
assert_eq!(els[2], PathEl::LineTo(Point::new(30.0, 10.0)));
assert_eq!(els[3], PathEl::LineTo(Point::new(30.0, 20.0)));
assert!(els.iter().any(|e| matches!(e, PathEl::ClosePath)));
// Relative move after Z is relative to the subpath start (10,10).
assert!(els.contains(&PathEl::MoveTo(Point::new(15.0, 15.0))));
// "l1-1.5.5.5e1": two implicit linetos (1,-1.5) then (.5,5).
assert!(els.contains(&PathEl::LineTo(Point::new(16.0, 13.5))));
assert!(els.contains(&PathEl::LineTo(Point::new(16.5, 18.5))));
assert!(els.iter().filter(|e| matches!(e, PathEl::CurveTo(..))).count() >= 4);
}
#[test]
fn errors_keep_prefix() {
let p = parse_path_data("M0 0 L10 0 L10 x10 L0 10");
assert_eq!(p.elements().len(), 2);
assert!(parse_path_data("garbage").elements().is_empty());
assert!(parse_path_data("").elements().is_empty());
}
#[test]
fn number_after_close_stops_instead_of_looping() {
// "Z9": Z was repeated implicitly without consuming the number, appending close-paths
// until memory ran out.
let p = parse_path_data("M0 0 L10 0 L10 10 Z9 C1 2 3 4 5 6");
assert_eq!(p.elements().len(), 4);
assert!(parse_path_data("M0 0 L10 0 z 9 9").elements().len() <= 4);
}
#[test]
fn number_lists() {
assert_eq!(numbers("0 0,100 50"), vec![0.0, 0.0, 100.0, 50.0]);
assert_eq!(numbers("-1-2.5.5"), vec![-1.0, -2.5, 0.5]);
assert_eq!(numbers("1e2,2E-1"), vec![100.0, 0.2]);
}
}
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