Function advance_segment_to_x

src/plot_state.rs:1054–1059

(points: &[[f64; 2]], seg_idx: &mut usize, x: f64)

        })
        .collect()
}

/// Keep only strictly increasing-x points in their original order.
///
/// This avoids sorting and lets fill interpolation run in linear time.
/// Out-of-order (or duplicate-x) points are skipped.
fn monotonic_increasing_x(points: Vec<[f64; 2]>) -> Vec<[f64; 2]> {
    let mut out = Vec::with_capacity(points.len());
    let mut last_x: Option<f64> = None;