Add dashed line style.

[KmolYuan]

A simple work similar to LineSeries and PathElement.

New Types

Added DashedLineSeries (under line_series feature) and DashedPathElement.

• plotters::series::line_series::DashedLineSeries - A simple type just making std::iter::once(element) by implementing IntoIterator, and has the same options as the element type.
• plotters::element::basic_shapes::DashedPathElement - A element type drawing dashed lines pixel-wised.

Options

• points: The iterator of the points.
• size: The dash size.
• spacing: The dash-to-dash spacing (gap size).
• style: The shape style.

⚠️ Known Issue

• If the points are too dense, it will become a solid line. (solved)
• Distortion in rounding coordinates, mainly in SVG.

Preview

Use blue line. The cross markers are the input points.

let series = DashedLineSeries::new(points, 10, 5, color);
chart.draw_series(series)?.label(label).legend(move |(x, y)| {
    DashedPathElement::new([(x, y), (x + 20, y)], 10, 5, color)
});

Another SVG example of my work is 3D coordinates. The curves are projected on a sphere, the main shape using a red dashed line, and the mechanism behind the sphere is shown with gray dashed lines.

[KmolYuan]

This is a solution for anyone who wants to use dashed lines.
References: #321 #295 #324

[AaronErhardt]

Looks good to me. Is it ready to merge?

[KmolYuan]

@AaronErhardt Sure, thanks for your review!

[gitmalong]

Does this also allow configure_series_labels to use a dashed border?

[KmolYuan]

@gitmalong

Does this also allow configure_series_labels to use a dashed border?

Currently not. It needs a custom drawing function setting for the border style.