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Refactor eval_pathseg_euclidean() to use kurbo's faster/more accurate inv_arclen() #3969

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Merged
Keavon merged 1 commit into from
Mar 28, 2026
+4 −28
Merged

Refactor eval_pathseg_euclidean() to use kurbo's faster/more accurate inv_arclen() #3969

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32 changes: 4 additions & 28 deletions node-graph/libraries/vector-types/src/vector/algorithms/bezpath_algorithms.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,7 @@ use crate::vector::misc::{PointSpacingType, dvec2_to_point, point_to_dvec2};
use core_types::math::polynomial::pathseg_to_parametric_polynomial;
use glam::{DMat2, DVec2};
use kurbo::common::{solve_cubic, solve_quadratic};
use kurbo::{BezPath, CubicBez, DEFAULT_ACCURACY, Line, ParamCurve, ParamCurveDeriv, PathEl, PathSeg, Point, QuadBez, Rect, Shape, Vec2};
use kurbo::{BezPath, CubicBez, DEFAULT_ACCURACY, Line, ParamCurve, ParamCurveArclen, ParamCurveDeriv, PathEl, PathSeg, Point, QuadBez, Rect, Shape, Vec2};
use std::f64::consts::{FRAC_PI_2, PI};

/// Splits the [`BezPath`] at segment index at `t` value which lie in the range of [0, 1].
Expand Down Expand Up @@ -342,34 +342,10 @@ pub(crate) fn pathseg_length_centroid_and_length(segment: PathSeg, accuracy: Opt
}
}

/// Finds the t value of point on the given path segment i.e fractional distance along the segment's total length.
/// It uses a binary search to find the value `t` such that the ratio `length_up_to_t / total_length` approximates the input `distance`.
/// Finds the parametric `t` value on the given path segment corresponding to a fractional arc-length `distance` (0–1).
/// Delegates to kurbo's `inv_arclen` which uses the ITP method with incremental arc-length computation.
pub fn eval_pathseg_euclidean(segment: PathSeg, distance: f64, accuracy: f64) -> f64 {
let mut low_t = 0.;
let mut mid_t = 0.5;
let mut high_t = 1.;

let total_length = segment.perimeter(accuracy);

if !total_length.is_finite() || total_length <= f64::EPSILON {
return 0.;
}

let distance = distance.clamp(0., 1.);

while high_t - low_t > accuracy {
let current_length = segment.subsegment(0.0..mid_t).perimeter(accuracy);
let current_distance = current_length / total_length;

if current_distance > distance {
high_t = mid_t;
} else {
low_t = mid_t;
}
mid_t = (high_t + low_t) / 2.;
}

mid_t
segment.inv_arclen(distance.clamp(0., 1.) * segment.arclen(accuracy), accuracy)
}

/// Converts from a bezpath (composed of multiple segments) to a point along a certain segment represented.
Expand Down
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