Documentation
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Overview ¶
Package scale maps data values onto visual positions and generates the ticks that label them.
A Scale owns two things: the domain→range mapping, and the choice of tick positions and labels for that domain. Keeping both in one place is what lets a time axis label itself in calendar units while a linear axis labels itself with round numbers, without either the geom or the layout knowing which is which.
Index ¶
Constants ¶
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Variables ¶
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Functions ¶
Types ¶
type LinearOption ¶
type LinearOption func(*linear)
LinearOption configures a linear scale.
func Domain ¶
func Domain(min, max float64) LinearOption
Domain pins the data domain explicitly, disabling training.
func Format ¶
func Format(fn func(v float64) string) LinearOption
Format overrides tick label formatting.
func Nice ¶
func Nice() LinearOption
Nice expands the domain outwards to the tick sequence's own bounds, so the axis starts and ends on a labelled tick rather than on the extreme data value. This is what most charts want and what CONCEPT.md §13 shows.
func Zero ¶
func Zero() LinearOption
Zero forces the domain to include zero. Bar charts need this: a bar chart whose baseline is off-screen misleads.
type Scale ¶
type Scale interface {
// Train extends the scale's data domain to include vs. Values that are
// NaN or infinite are ignored. Calling Train repeatedly accumulates.
Train(vs ...float64)
// SetRange sets the device-space output interval. lo may be greater than
// hi, which is how a Y axis is flipped so that larger values are higher on
// screen.
SetRange(lo, hi float32)
// Domain reports the current data domain, after any nicing.
Domain() (min, max float64)
// Map converts a data value to a device position. Values outside the
// domain map outside the range; clipping is the caller's business.
Map(v float64) float32
// Invert converts a device position back to a data value. It is the
// inverse of Map over the whole real line, not just the range.
Invert(pos float32) float64
// Ticks returns tick positions and labels, aiming for about want ticks.
// The result is ordered ascending by Value.
Ticks(want int) []Tick
}
Scale maps data values onto a device-space range.
A scale is trained on data, given a device range, and then queried. The order matters: Map and Ticks are only meaningful once both the domain and the range are set.
type Tick ¶
type Tick struct {
// Value is the tick's position in data space.
Value float64
// Pos is the tick's position in device space, already mapped.
Pos float32
// Label is the formatted text for the tick. An empty label means a tick
// mark and grid line are drawn but nothing is written.
Label string
// Minor marks a tick that subdivides the axis without a label.
Minor bool
}
Tick is one labelled position on an axis.
type TimeOption ¶
type TimeOption func(*timeScale)
TimeOption configures a time scale.
func In ¶
func In(loc *time.Location) TimeOption
In sets the location used to compute calendar ticks and format labels. The default is time.UTC, so that a chart renders identically wherever it is built — a server rendering in the client's local zone is a bug, not a feature.
func TimeFormat ¶
TimeFormat overrides tick label formatting. The unit the tick sequence settled on is passed so a caller can vary detail with zoom level.
Source Files