Add dotted line style

[KmolYuan]

A flexible line style that can insert custom markers at equal intervals and supports shifting.
#295 #321 #324 #483

New Types

• plotters::series::line_series::DottedLineSeries
• plotters::element::basic_shapes::DottedPathElement

Options in fn new(...) -> Self:

• points: The iterator of the points
• shift: The shift of the first marker
• spacing: The spacing between markers
• func: The marker function (Similar to the legend function, already mapped coordinates impl Fn(BackendCoord) -> Marker + 'static where Marker: IntoDynElement<'static, DB, BackendCoord>)

Examples

Basic Example

let mk_f = |c| Circle::new(c, 3, BLACK);
chart
    .draw_series(DottedLineSeries::new(points, /*shift*/ 0, /*spacing*/ 20, mk_f))?
    .label("Legend Text")
    .legend(move |c| {
        EmptyElement::at(c)
            + DottedPathElement::new([(gap, 0), (font - gap, 0)], 0, 20, mk_f)
    });

Left: point distance less than spacing
Right: point distance greater than spacing

Dash-dotted Line Example

Combined with the new dashed-line style! 🎉 (#483)

chart.draw_series(DashedLineSeries::new(points.clone(), 30, 16, color))?;
let dot_size = color.stroke_width / 2;
let mk_f = move |c| Circle::new(c, dot_size, color.filled());
chart
    .draw_series(DottedLineSeries::new(points, 30 + 8, 30 + 16, mk_f))?
    .label("Legend Text")
    .legend(move |c| {
        let points = [(gap, 0), (font - gap, 0)];
        EmptyElement::at(c)
            + DashedPathElement::new(points, 30, 16, color)
            + DottedPathElement::new(points, 30 + 8, 30 + 16, mk_f)
    });

Left: point distance less than spacing
Right: point distance greater than spacing

[AaronErhardt]

Looks good, thanks!