unit

Documentation

Overview

Package unit defines units of length such as inches or pixels.

Functions like Inches and Pixels return a Value in the corresponding unit. For example:

v := unit.Inches(4.5)

represents four and a half inches.

Converting between pixels (px), physical units (dp, pt, in, mm) and font-face-relative measures (em, ex, ch) depends on the context, such as the screen's DPI resolution and the active font face. That context is represented by the Converter type.

Conversions may be lossy. Converting 4.5 inches to pixels and back may result in something slightly different than 4.5. Similarly, converting 4 inches and 0.5 inches to pixels and then adding the results won't necessarily equal the conversion of 4.5 inches to pixels.

Note that what CSS (Cascading Style Sheets) calls "px" differs from what this package calls "px". For legacy reasons, the CSS semantics are that 1 inch should roughly equal 96csspx regardless of the actual DPI resolution, as per https://developer.mozilla.org/en/docs/Web/CSS/length. This package's semantics are that 1px means exactly one physical pixel, always. This package represents 1csspx as 1.666666667dp, since there are 160 density independent pixels per inch, the same definition as Android.

Index

• Constants
• type Converter
• type Unit
• type Value
  • func Chs(f float64) Value
  • func DIPs(f float64) Value
  • func Ems(f float64) Value
  • func Exs(f float64) Value
  • func Inches(f float64) Value
  • func Millimetres(f float64) Value
  • func Pixels(f float64) Value
  • func Points(f float64) Value
  • func (v Value) String() string

Constants

const (
	DensityIndependentPixelsPerInch = 160
	MillimetresPerInch              = 25.4
	PointsPerInch                   = 72
)

Types

type Converter

type Converter interface {
	// Convert converts v to the given unit.
	Convert(v Value, to Unit) Value

	// Pixels converts v to a 26.6 fixed-point number of physical pixels.
	Pixels(v Value) fixed.Int26_6
}

Converter converts values from one unit to another. Conversions may be lossy.

type Unit

type Unit uint8

Unit is a unit of length, such as inches or pixels.

const (
	// Px is a physical pixel, regardless of the DPI resolution.
	Px Unit = iota

	// Dp is 1 density independent pixel: 1/160th of an inch.
	Dp
	// Pt is 1 point: 1/72th of an inch.
	Pt
	// Mm is 1 millimetre: 1/25.4th of an inch.
	Mm
	// In is 1 inch.
	//
	// If the context does not specify a DPI resolution, the recommended
	// fallback value for conversion is 72 pixels per inch.
	In

	// Em is the height of the active font face, disregarding extra leading
	// such as from double-spaced lines of text.
	//
	// If the context does not specify an active font face, the recommended
	// fallback value for conversion is 12pt.
	Em
	// Ex is the x-height of the active font face.
	//
	// If the context does not specify an x-height, the recommended fallback
	// value for conversion is 0.5em.
	Ex
	// Ch is the character width of the numeral zero glyph '0' of the active
	// font face.
	//
	// If the context does not specify a '0' glyph, the recommended fallback
	// value for conversion is 0.5em.
	Ch
)

type Value

type Value struct {
	F float64
	U Unit
}

Value is a number and a unit.

func Chs

func Chs(f float64) Value

Chs returns the given number of Ch as a Value.

func DIPs

func DIPs(f float64) Value

DIPs returns the given number of Dp as a Value.

func Ems

func Ems(f float64) Value

Ems returns the given number of Em as a Value.

func Exs

func Exs(f float64) Value

Exs returns the given number of Ex as a Value.

func Inches

func Inches(f float64) Value

Inches returns the given number of In as a Value.

func Millimetres

func Millimetres(f float64) Value

Millimetres returns the given number of Mm as a Value.

func Pixels

func Pixels(f float64) Value

Pixels returns the given number of Px as a Value.

func Points

func Points(f float64) Value

Points returns the given number of Pt as a Value.

func (Value) String

func (v Value) String() string

String implements the fmt.Stringer interface.