Function build_fill_span

src/plot_state.rs:1184–1302

(
    widget: &PlotWidget,
    begin: ShapeId,
    end: ShapeId,
    color: Color,
    x_domain: Option<(f64, f64)>,
    y_domain: Option<(f64, f64)>,
    axis_ranges: ([f64; 2], [f64; 2]),
)

    if a.len() < 2 || b.len() < 2 {
        return None;
    }

    let overlap_min = a.first()?[0].max(b.first()?[0]);
    let overlap_max = a.last()?[0].min(b.last()?[0]);
    if overlap_min >= overlap_max {
        return None;
    }

    let mut seg_a = find_segment_covering_x(&a, overlap_min)?;
    let mut seg_b = find_segment_covering_x(&b, overlap_min)?;

    let mut x_curr = overlap_min;
    let mut y_a_curr = y_at_x_in_segment(&a, seg_a, x_curr)?;
    let mut y_b_curr = y_at_x_in_segment(&b, seg_b, x_curr)?;

    let eps = 1e-12;
    loop {
        let next_a = a.get(seg_a + 1).map(|p| p[0]).unwrap_or(f64::INFINITY);
        let next_b = b.get(seg_b + 1).map(|p| p[0]).unwrap_or(f64::INFINITY);
        let x_next = next_a.min(next_b).min(overlap_max);

        if x_next <= x_curr + eps {
            break;
        }

        let y_a_next = y_at_x_in_segment(&a, seg_a, x_next)?;
        let y_b_next = y_at_x_in_segment(&b, seg_b, x_next)?;

        push_quad_as_triangles(
            vertices,
            [x_curr, y_a_curr],
            [x_curr, y_b_curr],
            [x_next, y_a_next],
            [x_next, y_b_next],
        );

        x_curr = x_next;
        y_a_curr = y_a_next;
        y_b_curr = y_b_next;

        if x_curr >= overlap_max - eps {
            break;
        }

        advance_segment_to_x(&a, &mut seg_a, x_curr);
        advance_segment_to_x(&b, &mut seg_b, x_curr);

        if seg_a + 1 >= a.len() || seg_b + 1 >= b.len() {
            break;
        }
    }

    Some(())
}

fn build_fill_span(
    widget: &PlotWidget,
    begin: ShapeId,