An ordinal scale to map discrete values (text or numeric) to a plotting coordinate system.

An ordinal scale is commonly used for the category axis in barcharts. It has to be able to generate the centre-point of the bar (e.g. for tick annotations) as well as the available width the bar or bar-group has to fill.

In order to do that the ordinal scale requires a 'padding' option to be set (defaults to 0.5 in the scale) that defines the gaps between the bars / categories. The ordinal scale has two mapping functions for the data domain to the plotting range. One returns the centre point (range_to_domain_fn) and one returns the "band" the category can occupy (domain_to_range_band_fn).

An OrdinalScale is initialised with a list of values which represent the categories. The scale generates a tick for each value in that list.

Typical usage of this scale would be as follows:

iex> category_scale
...> = Contex.OrdinalScale.new(["Hippo", "Turtle", "Rabbit"])
...> |> Contex.Scale.set_range(0.0, 9.0)
...> |> Contex.OrdinalScale.padding(2)
...> category_scale.domain_to_range_fn.("Turtle")
4.5
iex> category_scale.domain_to_range_band_fn.("Hippo")
{1.0, 2.0}
iex> category_scale.domain_to_range_band_fn.("Turtle")
{4.0, 5.0}