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Type: a hairline gap between vertical edges of a frame still splits the line

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Crossings of the middle of a line's band that lay within a few units of rounding of each other were joined as a seam, so two contours of an area type frame 1e-7 pt apart at x = 1e8 held one line across the gap between them. A vertical edge crosses the middle at its own x with no rounding, so a gap at one is no longer joined.
This commit is contained in:
dotCooCoo
2026-11-13 09:55:08 -08:00
parent ef331e8fad
commit 6664a9bdb1
1 changed files with 21 additions and 3 deletions
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crates/text/src/layout/region.rs
+21 -3
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@@ -226,10 +226,21 @@ fn band_intervals(polys: &[Vec<Point>], top: f64, bottom: f64) -> Vec<(f64, f64)
let (top, bottom) = (top.min(bottom), top.max(bottom));
// Contours that meet along an edge cross the middle of the band at the same x, up to a few
// units of rounding: the intervals on either side of it join (an edge that bounds the
// shape there is still subtracted below).
let mut mid = poly_intervals(polys, (top + bottom) * 0.5);
// shape there is still subtracted below). A vertical edge crosses the middle at its own x with
// no rounding, so a gap at one is never taken for a seam.
let y = (top + bottom) * 0.5;
let mut upright: Vec<f64> = polys
.iter()
.flat_map(|poly| poly.iter().zip(poly.iter().cycle().skip(1)))
.filter(|(a, b)| a.x == b.x && (a.y <= y) != (b.y <= y))
.map(|(a, _)| a.x)
.collect();
upright.sort_by(f64::total_cmp);
let upright = |x: f64| upright.binary_search_by(|v| v.total_cmp(&x)).is_ok();
let mut mid = poly_intervals(polys, y);
mid.dedup_by(|next, prev| {
let seam = next.0 - prev.1 <= 8.0 * f64::EPSILON * prev.1.abs().max(next.0.abs()).max(1.0);
let gap = next.0 - prev.1;
let seam = gap <= 8.0 * f64::EPSILON * prev.1.abs().max(next.0.abs()).max(1.0) && (gap <= 0.0 || !(upright(prev.1) || upright(next.0)));
if seam {
prev.1 = prev.1.max(next.1);
}
@@ -609,6 +620,13 @@ fn lines_cross_an_edge_two_contours_share() {
]);
let cells = Region::cells(&apart, &LayoutOptions::default(), &[]);
assert_spans(&cells[0].spans(40.0, 60.0), &[(x, x + 50.0), (x + 50.01, x + 100.0)]);
// So does a gap of 1e-7 pt between vertical edges there, a few units of rounding wide.
let apart = polygon_path(&[
&[(x, 0.0), (x + 50.0, 0.0), (x + 50.0, 100.0), (x, 100.0)],
&[(x + 50.0 + 1e-7, 0.0), (x + 100.0, 0.0), (x + 100.0, 100.0), (x + 50.0 + 1e-7, 100.0)],
]);
let cells = Region::cells(&apart, &LayoutOptions::default(), &[]);
assert_spans(&cells[0].spans(40.0, 60.0), &[(x, x + 50.0), (x + 50.0 + 1e-7, x + 100.0)]);
}
/// A frame of 200 thin slanted strips, whose edges in the band overlap in x far more than