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Browse / github.com/storytold/cadcraft / patch
Keep repeated-knot spline corners when tessellating
PNG/SVG tessellation clips repeated-knot spline corners while saved DXF remains exact (0.12.0) ## Summary CADCraft 0.12.0 on Windows can clip sharp, repeated-knot corners when tessellating a spline for PNG/SVG output, even though saving and reopening the DXF preserves the exact spline geometry. A new analytic 20 × 12 mm rectangle reproduces the issue. This fixture contains no production/project data, fonts or identifiers and is offered under CC0-1.0. ## Reproduce 1. Extract the attached synthetic test package. 2. Use the supplied DXF with CADCraft 0.12.0, or run the included generator with Python and ezdxf: `python generate_synthetic_corner.py --cadcraft PATH_TO_CADCRAFT_CLI` 3. Th
- Status
- open
- Score
- 0.00
- Adopters
- 0 other operators
- Author
- Silvertree2010 (imported from pull request #2129, open)
- Base
e86d895ba1086a7efc2a83048348f89098282d08- Size
- +88 −1 in 1 file
- Review
- pending
- Shared
- 2026-10-28
- Id
04edcb9a96f67cab47bee876
How it went
No other operator has reported using it yet.
Diff
raw · crates/geom/src/spline.rs
@@ -117,7 +117,28 @@ impl Spline { if !self.is_valid() { return self.control.clone(); }- self.samples(self.sample_count(tol)).collect()+ let n = self.sample_count(tol);+ let spans = self.knot_spans().count();+ if spans == 0 || spans > MAX_SAMPLES {+ return self.samples(n).collect();+ }+ // Sample each knot span on its own grid, its ends included, so a corner at a repeated+ // knot (C0 when the multiplicity reaches the degree) is a vertex of the result. The `n`+ // segments are shared out by span length, at least one per span; when that would pass+ // `MAX_SAMPLES` the share shrinks to keep within it.+ let (lo, hi) = self.domain();+ // The span's share of the domain first, so huge knots do not overflow the product.+ let segments = |budget: usize, (a, b): (f64, f64)| 1usize.max((budget as f64 * ((b - a) / (hi - lo))).round() as usize);+ let budget = if self.knot_spans().map(|s| segments(n, s)).sum::<usize>() <= MAX_SAMPLES { n } else { MAX_SAMPLES - spans };+ let mut out = Vec::with_capacity(n + spans + 1);+ out.push(self.eval_valid(lo, lo, hi));+ for (a, b) in self.knot_spans() {+ let seg = segments(budget, (a, b));+ for i in 1..=seg {+ out.push(self.eval_valid(a + (b - a) * i as f64 / seg as f64, lo, hi));+ }+ }+ out } /// How many segments a tessellation at `tol` takes: the control-polygon length guides it,@@ -631,4 +652,70 @@ mod tests { assert!(s.is_valid()); assert!(s.tessellate(1e-3).len() > 4); }++ /// A 20 × 12 rectangle as one closed cubic with triple internal knots at irrational+ /// parameters (#2055): every corner is a C0 knot no uniform parameter grid hits.+ fn rectangle(scale: f64) -> Spline {+ let (a, b, c) = (2f64.sqrt() / 100.0, 3f64.sqrt() / 50.0, 5f64.sqrt() / 40.0);+ let mut knots = vec![0.0; 4];+ for k in [a, b, c] {+ knots.extend([k; 3]);+ }+ knots.extend([1.0; 4]);+ let pts = [+ (0.0, 0.0),+ (20.0 / 3.0, 0.0),+ (40.0 / 3.0, 0.0),+ (20.0, 0.0),+ (20.0, 4.0),+ (20.0, 8.0),+ (20.0, 12.0),+ (40.0 / 3.0, 12.0),+ (20.0 / 3.0, 12.0),+ (0.0, 12.0),+ (0.0, 8.0),+ (0.0, 4.0),+ (0.0, 0.0),+ ];+ let control = pts.iter().map(|&(x, y)| Vec2::new(x * scale, y * scale)).collect();+ Spline { degree: 3, knots, control, weights: vec![1.0; 13], closed: true, ..Spline::default() }+ }++ #[test]+ fn tessellation_keeps_repeated_knot_corners() {+ for scale in [1.0, 1000.0] {+ let s = rectangle(scale);+ assert!(s.is_valid());+ let corners = [(0.0, 0.0), (20.0, 0.0), (20.0, 12.0), (0.0, 12.0)].map(|(x, y)| Vec2::new(x * scale, y * scale));+ for tol in [0.1, 0.01, 0.001, 1e-6] {+ let pts = s.tessellate(tol * scale);+ assert!(pts.len() <= MAX_SAMPLES + 1, "{} points", pts.len());+ for c in corners {+ let near = pts.iter().map(|p| p.dist(c)).fold(f64::INFINITY, f64::min);+ assert!(near <= 1e-9 * scale, "corner {c:?} missing at tol {tol}, nearest vertex {near}");+ }+ assert!(pts.windows(2).all(|w| w[0] != w[1]), "zero-length join at tol {tol}");+ }+ }+ }++ #[test]+ fn tessellation_of_a_smooth_rational_span_stays_within_tolerance() {+ // A quarter circle as a rational quadratic Bezier.+ let h = std::f64::consts::FRAC_1_SQRT_2;+ let s = Spline {+ degree: 2,+ knots: vec![0.0, 0.0, 0.0, 1.0, 1.0, 1.0],+ control: vec![Vec2::new(10.0, 0.0), Vec2::new(10.0, 10.0), Vec2::new(0.0, 10.0)],+ weights: vec![1.0, h, 1.0],+ ..Spline::default()+ };+ for tol in [0.1, 0.01, 0.001] {+ let pts = s.tessellate(tol);+ for w in pts.windows(2) {+ let mid = (w[0] + w[1]) * 0.5;+ assert!(10.0 - mid.dist(Vec2::ZERO) <= tol, "chord sag over {tol}");+ }+ }+ } }