sfnt

package
v2.0.1+incompatible Latest Latest
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 Go to latest Published: Sep 21, 2023 License: BSD-3-Clause Imports: 9 Imported by: 0

Documentation

Overview

Package sfnt implements a decoder for SFNT font file formats, including TrueType and OpenType.

Example (RasterizeGlyph) 
package main

import (
	"image"
	"image/draw"
	"log"
	"os"

	"git.fireandbrimst.one/aw/golang-image/font/gofont/goregular"
	"git.fireandbrimst.one/aw/golang-image/font/sfnt"
	"git.fireandbrimst.one/aw/golang-image/math/fixed"
	"git.fireandbrimst.one/aw/golang-image/vector"
)

func main() {
	const (
		ppem    = 32
		width   = 24
		height  = 36
		originX = 0
		originY = 32
	)

	f, err := sfnt.Parse(goregular.TTF)
	if err != nil {
		log.Fatalf("Parse: %v", err)
	}
	var b sfnt.Buffer
	x, err := f.GlyphIndex(&b, 'Ġ')
	if err != nil {
		log.Fatalf("GlyphIndex: %v", err)
	}
	if x == 0 {
		log.Fatalf("GlyphIndex: no glyph index found for the rune 'Ġ'")
	}
	segments, err := f.LoadGlyph(&b, x, fixed.I(ppem), nil)
	if err != nil {
		log.Fatalf("LoadGlyph: %v", err)
	}

	r := vector.NewRasterizer(width, height)
	r.DrawOp = draw.Src
	for _, seg := range segments {
		// The divisions by 64 below is because the seg.Args values have type
		// fixed.Int26_6, a 26.6 fixed point number, and 1<<6 == 64.
		switch seg.Op {
		case sfnt.SegmentOpMoveTo:
			r.MoveTo(
				originX+float32(seg.Args[0].X)/64,
				originY+float32(seg.Args[0].Y)/64,
			)
		case sfnt.SegmentOpLineTo:
			r.LineTo(
				originX+float32(seg.Args[0].X)/64,
				originY+float32(seg.Args[0].Y)/64,
			)
		case sfnt.SegmentOpQuadTo:
			r.QuadTo(
				originX+float32(seg.Args[0].X)/64,
				originY+float32(seg.Args[0].Y)/64,
				originX+float32(seg.Args[1].X)/64,
				originY+float32(seg.Args[1].Y)/64,
			)
		case sfnt.SegmentOpCubeTo:
			r.CubeTo(
				originX+float32(seg.Args[0].X)/64,
				originY+float32(seg.Args[0].Y)/64,
				originX+float32(seg.Args[1].X)/64,
				originY+float32(seg.Args[1].Y)/64,
				originX+float32(seg.Args[2].X)/64,
				originY+float32(seg.Args[2].Y)/64,
			)
		}
	}

	dst := image.NewAlpha(image.Rect(0, 0, width, height))
	r.Draw(dst, dst.Bounds(), image.Opaque, image.Point{})

	const asciiArt = ".++8"
	buf := make([]byte, 0, height*(width+1))
	for y := 0; y < height; y++ {
		for x := 0; x < width; x++ {
			a := dst.AlphaAt(x, y).A
			buf = append(buf, asciiArt[a>>6])
		}
		buf = append(buf, '\n')
	}
	os.Stdout.Write(buf)

}

Output:

........................
........................
........................
............888.........
............888.........
............888.........
............+++.........
........................
..........+++++++++.....
.......+8888888888888+..
......8888888888888888..
....+8888+........++88..
....8888................
...8888.................
..+888+.................
..+888..................
..888+..................
.+888+..................
.+888...................
.+888...................
.+888...................
.+888..........+++++++..
.+888..........8888888..
.+888+.........+++8888..
..888+............+888..
..8888............+888..
..+888+...........+888..
...8888+..........+888..
...+8888+.........+888..
....+88888+.......+888..
.....+8888888888888888..
.......+888888888888++..
..........++++++++......
........................
........................
........................

Index

Examples

Constants

View Source 
const (
	NameIDCopyright                  NameID = 0
	NameIDFamily                            = 1
	NameIDSubfamily                         = 2
	NameIDUniqueIdentifier                  = 3
	NameIDFull                              = 4
	NameIDVersion                           = 5
	NameIDPostScript                        = 6
	NameIDTrademark                         = 7
	NameIDManufacturer                      = 8
	NameIDDesigner                          = 9
	NameIDDescription                       = 10
	NameIDVendorURL                         = 11
	NameIDDesignerURL                       = 12
	NameIDLicense                           = 13
	NameIDLicenseURL                        = 14
	NameIDTypographicFamily                 = 16
	NameIDTypographicSubfamily              = 17
	NameIDCompatibleFull                    = 18
	NameIDSampleText                        = 19
	NameIDPostScriptCID                     = 20
	NameIDWWSFamily                         = 21
	NameIDWWSSubfamily                      = 22
	NameIDLightBackgroundPalette            = 23
	NameIDDarkBackgroundPalette             = 24
	NameIDVariationsPostScriptPrefix        = 25
)

Variables

View Source 
var (
	// ErrColoredGlyph indicates that the requested glyph is not a monochrome
	// vector glyph, such as a colored (bitmap or vector) emoji glyph.
	ErrColoredGlyph = errors.New("sfnt: colored glyph")
	// ErrNotFound indicates that the requested value was not found.
	ErrNotFound = errors.New("sfnt: not found")
)

Functions

This section is empty.

Types

type Buffer 

type Buffer struct {
	// contains filtered or unexported fields
}

Buffer holds re-usable buffers that can reduce the total memory allocation of repeated Font method calls.

See the Font type's documentation comment for more details.

type Collection 

type Collection struct {
	// contains filtered or unexported fields
}

Collection is a collection of one or more fonts.

All of the Collection methods are safe to call concurrently.

func ParseCollection 

func ParseCollection(src []byte) (*Collection, error)

ParseCollection parses an SFNT font collection, such as TTC or OTC data, from a []byte data source.

If passed data for a single font, a TTF or OTF instead of a TTC or OTC, it will return a collection containing 1 font.

func ParseCollectionReaderAt 

func ParseCollectionReaderAt(src io.ReaderAt) (*Collection, error)

ParseCollectionReaderAt parses an SFNT collection, such as TTC or OTC data, from an io.ReaderAt data source.

If passed data for a single font, a TTF or OTF instead of a TTC or OTC, it will return a collection containing 1 font.

func (*Collection) Font 

func (c *Collection) Font(i int) (*Font, error)

Font returns the i'th font in the collection.

func (*Collection) NumFonts 

func (c *Collection) NumFonts() int

NumFonts returns the number of fonts in the collection.

type Font 

type Font struct {
	// contains filtered or unexported fields
}

Font is an SFNT font.

Many of its methods take a *Buffer argument, as re-using buffers can reduce the total memory allocation of repeated Font method calls, such as measuring and rasterizing every unique glyph in a string of text. If efficiency is not a concern, passing a nil *Buffer is valid, and implies using a temporary buffer for a single call.

It is valid to re-use a *Buffer with multiple Font method calls, even with different *Font receivers, as long as they are not concurrent calls.

All of the Font methods are safe to call concurrently, as long as each call has a different *Buffer (or nil).

The Font methods that don't take a *Buffer argument are always safe to call concurrently.

Some methods provide lengths or coordinates, e.g. bounds, font metrics and control points. All of these methods take a ppem parameter, which is the number of pixels in 1 em, expressed as a 26.6 fixed point value. For example, if 1 em is 10 pixels then ppem is fixed.I(10), which equals fixed.Int26_6(10 << 6).

To get those lengths or coordinates in terms of font units instead of pixels, use ppem = fixed.Int26_6(f.UnitsPerEm()) and if those methods take a font.Hinting parameter, use font.HintingNone. The return values will have type fixed.Int26_6, but those numbers can be converted back to Units with no further scaling necessary.

func Parse 

func Parse(src []byte) (*Font, error)

Parse parses an SFNT font, such as TTF or OTF data, from a []byte data source.

func ParseReaderAt 

func ParseReaderAt(src io.ReaderAt) (*Font, error)

ParseReaderAt parses an SFNT font, such as TTF or OTF data, from an io.ReaderAt data source.

func (*Font) Bounds 

func (f *Font) Bounds(b *Buffer, ppem fixed.Int26_6, h font.Hinting) (fixed.Rectangle26_6, error)

Bounds returns the union of a Font's glyphs' bounds.

In the returned Rectangle26_6's (x, y) coordinates, the Y axis increases down.

func (*Font) GlyphAdvance 

func (f *Font) GlyphAdvance(b *Buffer, x GlyphIndex, ppem fixed.Int26_6, h font.Hinting) (fixed.Int26_6, error)

GlyphAdvance returns the advance width for the x'th glyph. ppem is the number of pixels in 1 em.

It returns ErrNotFound if the glyph index is out of range.

func (*Font) GlyphIndex 

func (f *Font) GlyphIndex(b *Buffer, r rune) (GlyphIndex, error)

GlyphIndex returns the glyph index for the given rune.

It returns (0, nil) if there is no glyph for r. https://www.microsoft.com/typography/OTSPEC/cmap.htm says that "Character codes that do not correspond to any glyph in the font should be mapped to glyph index 0. The glyph at this location must be a special glyph representing a missing character, commonly known as .notdef."

func (*Font) GlyphName 

func (f *Font) GlyphName(b *Buffer, x GlyphIndex) (string, error)

GlyphName returns the name of the x'th glyph.

Not every font contains glyph names. If not present, GlyphName will return ("", nil).

If present, the glyph name, provided by the font, is assumed to follow the Adobe Glyph List Specification: https://github.com/adobe-type-tools/agl-specification/blob/master/README.md

This is also known as the "Adobe Glyph Naming convention", the "Adobe document [for] Unicode and Glyph Names" or "PostScript glyph names".

It returns ErrNotFound if the glyph index is out of range.

func (*Font) Kern 

func (f *Font) Kern(b *Buffer, x0, x1 GlyphIndex, ppem fixed.Int26_6, h font.Hinting) (fixed.Int26_6, error)

Kern returns the horizontal adjustment for the kerning pair (x0, x1). A positive kern means to move the glyphs further apart. ppem is the number of pixels in 1 em.

It returns ErrNotFound if either glyph index is out of range.

func (*Font) LoadGlyph 

func (f *Font) LoadGlyph(b *Buffer, x GlyphIndex, ppem fixed.Int26_6, opts *LoadGlyphOptions) ([]Segment, error)

LoadGlyph returns the vector segments for the x'th glyph. ppem is the number of pixels in 1 em.

If b is non-nil, the segments become invalid to use once b is re-used.

In the returned Segments' (x, y) coordinates, the Y axis increases down.

It returns ErrNotFound if the glyph index is out of range. It returns ErrColoredGlyph if the glyph is not a monochrome vector glyph, such as a colored (bitmap or vector) emoji glyph.

func (*Font) Metrics 

func (f *Font) Metrics(b *Buffer, ppem fixed.Int26_6, h font.Hinting) (font.Metrics, error)

Metrics returns the metrics of this font.

func (*Font) Name 

func (f *Font) Name(b *Buffer, id NameID) (string, error)

Name returns the name value keyed by the given NameID.

It returns ErrNotFound if there is no value for that key.

func (*Font) NumGlyphs 

func (f *Font) NumGlyphs() int

NumGlyphs returns the number of glyphs in f.

func (*Font) PostTable 

func (f *Font) PostTable() *PostTable

PostTable returns the information from the font's "post" table. It can return nil, if the font doesn't have such a table.

See https://docs.microsoft.com/en-us/typography/opentype/spec/post

func (*Font) UnitsPerEm 

func (f *Font) UnitsPerEm() Units

UnitsPerEm returns the number of units per em for f.

type GlyphIndex 

type GlyphIndex uint16

GlyphIndex is a glyph index in a Font.

type LoadGlyphOptions 

type LoadGlyphOptions struct {
}

LoadGlyphOptions are the options to the Font.LoadGlyph method.

type NameID 

type NameID uint16

NameID identifies a name table entry.

See the "Name IDs" section of https://www.microsoft.com/typography/otspec/name.htm

type PostTable 

type PostTable struct {
	// Version of the version tag of the "post" table.
	Version uint32
	// ItalicAngle in counter-clockwise degrees from the vertical. Zero for
	// upright text, negative for text that leans to the right (forward).
	ItalicAngle float64
	// UnderlinePosition is the suggested distance of the top of the
	// underline from the baseline (negative values indicate below baseline).
	UnderlinePosition int16
	// Suggested values for the underline thickness.
	UnderlineThickness int16
	// IsFixedPitch indicates that the font is not proportionally spaced
	// (i.e. monospaced).
	IsFixedPitch bool
}

PostTable represents an information stored in the PostScript font section.

type Segment 

type Segment struct {
	// Op is the operator.
	Op SegmentOp
	// Args is up to three (x, y) coordinates. The Y axis increases down.
	Args [3]fixed.Point26_6
}

Segment is a segment of a vector path.

type SegmentOp 

type SegmentOp uint32

SegmentOp is a vector path segment's operator. 

const (
	SegmentOpMoveTo SegmentOp = iota
	SegmentOpLineTo
	SegmentOpQuadTo
	SegmentOpCubeTo
)

type Units 

type Units int32

Units are an integral number of abstract, scalable "font units". The em square is typically 1000 or 2048 "font units". This would map to a certain number (e.g. 30 pixels) of physical pixels, depending on things like the display resolution (DPI) and font size (e.g. a 12 point font).

Source Files

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