Function series_points_are_paired

src/plot_state.rs:1071–1095

(a: &[[f64; 2]], b: &[[f64; 2]])

            }
        }
    }
    out
}

fn find_segment_covering_x(points: &[[f64; 2]], x: f64) -> Option<usize> {
    if points.len() < 2 {
        return None;
    }
    let eps = 1e-12;
    let mut idx = 0usize;
    while idx + 1 < points.len() {
        let x0 = points[idx][0];
        let x1 = points[idx + 1][0];
        if x >= x0 - eps && x <= x1 + eps {
            return Some(idx);
        }
        idx += 1;
    }
    None
}

fn y_at_x_in_segment(points: &[[f64; 2]], seg_idx: usize, x: f64) -> Option<f64> {
    let p0 = *points.get(seg_idx)?;
    let p1 = *points.get(seg_idx + 1)?;
    let x0 = p0[0];
    let x1 = p1[0];
    let eps = 1e-9;
    if x < x0 - eps || x > x1 + eps {