Core Concepts

The composition model

goplotlib uses three types arranged in a simple hierarchy:

Figure (size, theme)
  └── Axes (plot area, scales, labels)
        ├── LineChart (xs, ys, style)
        ├── BarChart  (categories, values, style)
        └── ScatterChart (xs, ys, style)

Figure

plot.Figure is the root container. It defines:

Width and height in pixels (WithWidth, WithHeight). Default: 900×550.
Theme — the visual style applied to every Axes it contains (WithTheme). Default: theme.Light.
Figure-level title shown centered above all Axes (WithTitle).

You create a Figure with plot.New(opts...) and render it with fig.SVG() (returns []byte) or fig.SaveSVG(path).

Axes

plot.Axes is a single rectangular plot area. One Axes occupies the full Figure. An Axes is responsible for:

Computing linear (or categorical) data scales from the union of all series’ ranges.
Drawing the grid, spines, tick marks, and tick labels.
Rendering each series clipped to the plot rectangle.
Drawing the legend when multiple labeled series are present.

Add an Axes by calling fig.AddAxes(). Configure it with method chaining:

ax := fig.AddAxes()
ax.SetTitle("My chart").
   SetXLabel("time").
   SetYLabel("value").
   Legend(plot.LegendOutsideRight)

Legend positioning

The legend appears automatically when multiple labeled series are present. Six positions are available — four inside the plot area and two outside it:

Position	Behaviour
`LegendTopRight` (default)	Inside, top-right corner
`LegendTopLeft`	Inside, top-left corner
`LegendBottomRight`	Inside, bottom-right corner
`LegendBottomLeft`	Inside, bottom-left corner
`LegendOutsideRight`	Vertical list to the right of the plot — never overlaps data
`LegendOutsideBottom`	Horizontal row below the plot — never overlaps data

Use ax.NoLegend() (or plot.LegendNone) to hide it entirely.

Chart (series)

A chart is a single data series. You never construct chart types directly — instead you call the corresponding Axes method, which creates the series and registers it:

Method	Series type
`ax.Line(xs, ys, chart.LineStyle{...})`	`chart.LineChart`
`ax.Bar(categories, values, chart.BarStyle{...})`	`chart.BarChart`
`ax.Scatter(xs, ys, chart.ScatterStyle{...})`	`chart.ScatterChart`

All three methods return the *Axes so you can chain multiple calls:

ax.Line(xs, ys1, chart.LineStyle{Label: "series A"}).
   Line(xs, ys2, chart.LineStyle{Label: "series B"})

Colors and themes

When a series is added without an explicit Color field in its style struct, the Figure automatically assigns the next color from the active theme’s palette. The Classic palette is used by Light, Dark, and Minimal themes. The FiveThirtyEight theme has its own palette.

You can override any series color explicitly:

ax.Line(xs, ys, chart.LineStyle{Color: color.Parse("#e63946")})