Class SeriesSpan

src/plot_state.rs:1305–1314

                series,
                widget.x_axis_scale,
                widget.y_axis_scale,
                axis_ranges,
            );
            for segment in points.windows(2) {
                let p0 = segment[0];
                let p1 = segment[1];
                let q0 = [x_plot, p0[1]];
                let q1 = [x_plot, p1[1]];
                push_quad_as_triangles(&mut vertices, p0, q0, p1, q1);
            }
        }
        (FillEndpoint::HLine(hline0), FillEndpoint::HLine(hline1)) => {
            let (x0, x1) = x_domain?;