Module series_pattern 

SeriesPattern — the non-colour channel that identifies a chart series.

A chart that tells its series apart by colour and nothing else fails WCAG 1.4.1 (Use of Color), whatever palette it uses. A CVD-safe palette like Okabe–Ito answers a different question — whether the colours are distinguishable from one another — and does not answer this one: a reader with monochrome vision, a monochrome printout, a display in bright sun, or a forced-colours setting has no colour channel at all. It also does not answer the wrap-around problem, where a ninth series repeats the first’s colour exactly.

So every series carries a second, orthogonal identity: a pattern. One value drives all three renderings a chart needs, so a series looks like itself whether it is drawn as a line, a bar, a slice, or a legend swatch:

	line	marker	filled area
Solid	solid	circle	plain
Dashed	long dash	square	45° hatch
Dotted	dotted	triangle	back-hatch
DashDot	dash-dot	diamond	cross-hatch
ShortDash	short dash	cross	horizontal
WideDash	wide dash	plus	vertical

Six patterns against the theme palette’s eight colours means the pair (colour, pattern) does not repeat until the 24th series — where colour alone repeated at the 9th.

A series with no explicit pattern is assigned one from its position by SeriesPattern::for_index, so the channel exists without any application code. Whether a chart draws it is the chart’s decision (the stock charts draw it once more than one series is visible, since a single-series chart has nothing to disambiguate).

Enums

SeriesHatch

How a filled region (a bar, an area, a pie slice) carries its series’ pattern. None is a plain fill; the rest are line hatches at the named angle, drawn in a contrasting tone over the fill.

SeriesMarker

The marker glyph drawn at a line chart’s data points, and next to a series in a legend. Shape, not colour — that is the whole point.

SeriesPattern

The non-colour visual channel identifying one chart series.