font

Documentation

Overview

Package font defines an interface for font faces, for drawing text on an image.

Other packages provide font face implementations. For example, a truetype package would provide one based on .ttf font files.

Index

• type Drawer
  • func (d *Drawer) DrawString(s string)
  • func (d *Drawer) MeasureString(s string) (advance fixed.Int26_6)
• type Face
• type Hinting
• type Stretch
• type Style
• type Weight

Types

type Drawer

type Drawer struct {
	// Dst is the destination image.
	Dst draw.Image
	// Src is the source image.
	Src image.Image
	// Face provides the glyph mask images.
	Face Face
	// Dot is the baseline location to draw the next glyph. The majority of the
	// affected pixels will be above and to the right of the dot, but some may
	// be below or to the left. For example, drawing a 'j' in an italic face
	// may affect pixels below and to the left of the dot.
	Dot fixed.Point26_6
}

Drawer draws text on a destination image.

A Drawer is not safe for concurrent use by multiple goroutines, since its Face is not.

func (*Drawer) DrawString

func (d *Drawer) DrawString(s string)

DrawString draws s at the dot and advances the dot's location.

func (*Drawer) MeasureString

func (d *Drawer) MeasureString(s string) (advance fixed.Int26_6)

MeasureString returns how far dot would advance by drawing s.

type Face

type Face interface {
	io.Closer

	// Glyph returns the draw.DrawMask parameters (dr, mask, maskp) to draw r's
	// glyph at the sub-pixel destination location dot, and that glyph's
	// advance width.
	//
	// It returns !ok if the face does not contain a glyph for r.
	//
	// The contents of the mask image returned by one Glyph call may change
	// after the next Glyph call. Callers that want to cache the mask must make
	// a copy.
	Glyph(dot fixed.Point26_6, r rune) (
		dr image.Rectangle, mask image.Image, maskp image.Point, advance fixed.Int26_6, ok bool)

	// GlyphBounds returns the bounding box of r's glyph, drawn at a dot equal
	// to the origin, and that glyph's advance width.
	//
	// It returns !ok if the face does not contain a glyph for r.
	//
	// The glyph's ascent and descent equal -bounds.Min.Y and +bounds.Max.Y. A
	// visual depiction of what these metrics are is at
	// https://developer.apple.com/library/mac/documentation/TextFonts/Conceptual/CocoaTextArchitecture/Art/glyph_metrics_2x.png
	GlyphBounds(r rune) (bounds fixed.Rectangle26_6, advance fixed.Int26_6, ok bool)

	// GlyphAdvance returns the advance width of r's glyph.
	//
	// It returns !ok if the face does not contain a glyph for r.
	GlyphAdvance(r rune) (advance fixed.Int26_6, ok bool)

	// Kern returns the horizontal adjustment for the kerning pair (r0, r1). A
	// positive kern means to move the glyphs further apart.
	Kern(r0, r1 rune) fixed.Int26_6
}

Face is a font face. Its glyphs are often derived from a font file, such as "Comic_Sans_MS.ttf", but a face has a specific size, style, weight and hinting. For example, the 12pt and 18pt versions of Comic Sans are two different faces, even if derived from the same font file.

A Face is not safe for concurrent use by multiple goroutines, as its methods may re-use implementation-specific caches and mask image buffers.

To create a Face, look to other packages that implement specific font file formats.

type Hinting

type Hinting int

Hinting selects how to quantize a vector font's glyph nodes.

Not all fonts support hinting.

const (
	HintingNone Hinting = iota
	HintingVertical
	HintingFull
)

type Stretch

type Stretch int

Stretch selects a normal, condensed, or expanded face.

Not all fonts support stretches.

const (
	StretchUltraCondensed Stretch = -4
	StretchExtraCondensed Stretch = -3
	StretchCondensed      Stretch = -2
	StretchSemiCondensed  Stretch = -1
	StretchNormal         Stretch = +0
	StretchSemiExpanded   Stretch = +1
	StretchExpanded       Stretch = +2
	StretchExtraExpanded  Stretch = +3
	StretchUltraExpanded  Stretch = +4
)

type Style

type Style int

Style selects a normal, italic, or oblique face.

Not all fonts support styles.

const (
	StyleNormal Style = iota
	StyleItalic
	StyleOblique
)

type Weight

type Weight int

Weight selects a normal, light or bold face.

Not all fonts support weights.

const (
	WeightThin       Weight = 100
	WeightExtraLight Weight = 200
	WeightLight      Weight = 300
	WeightNormal     Weight = 400
	WeightMedium     Weight = 500
	WeightSemiBold   Weight = 600
	WeightBold       Weight = 700
	WeightExtraBold  Weight = 800
	WeightBlack      Weight = 900
)