// Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package plan9font implements font faces for the Plan 9 font and subfont file
// formats. These formats are described at
// https://9p.io/magic/man2html/6/font
package plan9font // import "golang.org/x/image/font/plan9font"
import (
"bytes"
"errors"
"fmt"
"image"
"image/color"
"log"
"strconv"
"strings"
"golang.org/x/image/font"
"golang.org/x/image/math/fixed"
)
// fontchar describes one character glyph in a subfont.
//
// For more detail, look for "struct Fontchar" in
// https://9p.io/magic/man2html/2/cachechars
type fontchar struct {
x uint32 // X position in the image holding the glyphs.
top uint8 // First non-zero scan line.
bottom uint8 // Last non-zero scan line.
left int8 // Offset of baseline.
width uint8 // Width of baseline.
}
func parseFontchars(p []byte) []fontchar {
fc := make([]fontchar, len(p)/6)
for i := range fc {
fc[i] = fontchar{
x: uint32(p[0]) | uint32(p[1])<<8,
top: uint8(p[2]),
bottom: uint8(p[3]),
left: int8(p[4]),
width: uint8(p[5]),
}
p = p[6:]
}
return fc
}
// subface implements font.Face for a Plan 9 subfont.
type subface struct {
firstRune rune // First rune in the subfont.
n int // Number of characters in the subfont.
height int // Inter-line spacing.
ascent int // Height above the baseline.
fontchars []fontchar // Character descriptions.
img *image.Alpha // Image holding the glyphs.
}
func (f *subface) Close() error { return nil }
func (f *subface) Kern(r0, r1 rune) fixed.Int26_6 { return 0 }
func (f *subface) Metrics() font.Metrics {
// Approximate XHeight with the ascent of lowercase 'x'.
xbounds, _, _ := f.GlyphBounds('x')
// The same applies to CapHeight, using the uppercase 'H'.
hbounds, _, _ := f.GlyphBounds('H')
return font.Metrics{
Height: fixed.I(f.height),
Ascent: fixed.I(f.ascent),
Descent: fixed.I(f.height - f.ascent),
XHeight: -xbounds.Min.Y,
CapHeight: -hbounds.Min.Y,
CaretSlope: image.Point{X: 0, Y: 1},
}
}
func (f *subface) Glyph(dot fixed.Point26_6, r rune) (
dr image.Rectangle, mask image.Image, maskp image.Point, advance fixed.Int26_6, ok bool) {
r -= f.firstRune
if r < 0 || f.n <= int(r) {
return image.Rectangle{}, nil, image.Point{}, 0, false
}
i := &f.fontchars[r+0]
j := &f.fontchars[r+1]
minX := int(dot.X+32)>>6 + int(i.left)
minY := int(dot.Y+32)>>6 + int(i.top) - f.ascent
dr = image.Rectangle{
Min: image.Point{
X: minX,
Y: minY,
},
Max: image.Point{
X: minX + int(j.x-i.x),
Y: minY + int(i.bottom) - int(i.top),
},
}
return dr, f.img, image.Point{int(i.x), int(i.top)}, fixed.Int26_6(i.width) << 6, true
}
func (f *subface) GlyphBounds(r rune) (bounds fixed.Rectangle26_6, advance fixed.Int26_6, ok bool) {
r -= f.firstRune
if r < 0 || f.n <= int(r) {
return fixed.Rectangle26_6{}, 0, false
}
i := &f.fontchars[r+0]
j := &f.fontchars[r+1]
bounds = fixed.R(
int(i.left),
int(i.top)-f.ascent,
int(i.left)+int(j.x-i.x),
int(i.bottom)-f.ascent,
)
return bounds, fixed.Int26_6(i.width) << 6, true
}
func (f *subface) GlyphAdvance(r rune) (advance fixed.Int26_6, ok bool) {
r -= f.firstRune
if r < 0 || f.n <= int(r) {
return 0, false
}
return fixed.Int26_6(f.fontchars[r].width) << 6, true
}
// runeRange maps a single rune range [lo, hi] to a lazily loaded subface. Both
// ends of the range are inclusive.
type runeRange struct {
lo, hi rune
offset rune // subfont index that the lo rune maps to.
relFilename string
subface *subface
bad bool
}
// face implements font.Face for a Plan 9 font.
//
// It maps multiple rune ranges to *subface values. Rune ranges may overlap;
// the first match wins.
type face struct {
height int
ascent int
readFile func(relFilename string) ([]byte, error)
runeRanges []runeRange
}
func (f *face) Close() error { return nil }
func (f *face) Kern(r0, r1 rune) fixed.Int26_6 { return 0 }
func (f *face) Metrics() font.Metrics {
xbounds, _, _ := f.GlyphBounds('x')
hbounds, _, _ := f.GlyphBounds('H')
return font.Metrics{
Height: fixed.I(f.height),
Ascent: fixed.I(f.ascent),
Descent: fixed.I(f.height - f.ascent),
XHeight: -xbounds.Min.Y,
CapHeight: -hbounds.Min.Y,
CaretSlope: image.Point{X: 0, Y: 1},
}
}
func (f *face) Glyph(dot fixed.Point26_6, r rune) (
dr image.Rectangle, mask image.Image, maskp image.Point, advance fixed.Int26_6, ok bool) {
if s, rr := f.subface(r); s != nil {
return s.Glyph(dot, rr)
}
return image.Rectangle{}, nil, image.Point{}, 0, false
}
func (f *face) GlyphBounds(r rune) (bounds fixed.Rectangle26_6, advance fixed.Int26_6, ok bool) {
if s, rr := f.subface(r); s != nil {
return s.GlyphBounds(rr)
}
return fixed.Rectangle26_6{}, 0, false
}
func (f *face) GlyphAdvance(r rune) (advance fixed.Int26_6, ok bool) {
if s, rr := f.subface(r); s != nil {
return s.GlyphAdvance(rr)
}
return 0, false
}
// For subfont files, if reading the given file name fails, we try appending
// ".n" where n is the log2 of the grayscale depth in bits (so at most 3) and
// then work down to 0. This was done in Plan 9 when antialiased fonts were
// introduced so that the 1-bit displays could keep using the 1-bit forms but
// higher depth displays could use the antialiased forms.
var subfontSuffixes = [...]string{
"",
".3",
".2",
".1",
".0",
}
func (f *face) readSubfontFile(name string) ([]byte, error) {
var firstErr error
for _, suffix := range subfontSuffixes {
if b, err := f.readFile(name + suffix); err == nil {
return b, nil
} else if firstErr == nil {
firstErr = err
}
}
return nil, firstErr
}
func (f *face) subface(r rune) (*subface, rune) {
// Fall back on U+FFFD if we can't find r.
for _, rr := range [2]rune{r, '\ufffd'} {
// We have to do linear, not binary search. plan9port's
// lucsans/unicode.8.font says:
// 0x2591 0x2593 ../luc/Altshades.7.0
// 0x2500 0x25ee ../luc/FormBlock.7.0
// and the rune ranges overlap.
for i := range f.runeRanges {
x := &f.runeRanges[i]
if rr < x.lo || x.hi < rr || x.bad {
continue
}
if x.subface == nil {
data, err := f.readSubfontFile(x.relFilename)
if err != nil {
log.Printf("plan9font: couldn't read subfont %q: %v", x.relFilename, err)
x.bad = true
continue
}
sub, err := ParseSubfont(data, x.lo-x.offset)
if err != nil {
log.Printf("plan9font: couldn't parse subfont %q: %v", x.relFilename, err)
x.bad = true
continue
}
x.subface = sub.(*subface)
}
return x.subface, rr
}
}
return nil, 0
}
// ParseFont parses a Plan 9 font file. data is the contents of that font file,
// which gives relative filenames for subfont files. readFile returns the
// contents of those subfont files. It is similar to io/ioutil's ReadFile
// function, except that it takes a relative filename instead of an absolute
// one.
func ParseFont(data []byte, readFile func(relFilename string) ([]byte, error)) (font.Face, error) {
f := &face{
readFile: readFile,
}
// TODO: don't use strconv, to avoid the conversions from []byte to string?
for first := true; len(data) > 0; first = false {
i := bytes.IndexByte(data, '\n')
if i < 0 {
return nil, errors.New("plan9font: invalid font: no final newline")
}
row := string(data[:i])
data = data[i+1:]
if first {
height, s, ok := nextInt32(row)
if !ok {
return nil, fmt.Errorf("plan9font: invalid font: invalid header %q", row)
}
ascent, s, ok := nextInt32(s)
if !ok {
return nil, fmt.Errorf("plan9font: invalid font: invalid header %q", row)
}
if height < 0 || 0xffff < height || ascent < 0 || 0xffff < ascent {
return nil, fmt.Errorf("plan9font: invalid font: invalid header %q", row)
}
f.height, f.ascent = int(height), int(ascent)
continue
}
lo, s, ok := nextInt32(row)
if !ok {
return nil, fmt.Errorf("plan9font: invalid font: invalid row %q", row)
}
hi, s, ok := nextInt32(s)
if !ok {
return nil, fmt.Errorf("plan9font: invalid font: invalid row %q", row)
}
offset, s, _ := nextInt32(s)
f.runeRanges = append(f.runeRanges, runeRange{
lo: lo,
hi: hi,
offset: offset,
relFilename: s,
})
}
return f, nil
}
func nextInt32(s string) (ret int32, remaining string, ok bool) {
i := 0
for ; i < len(s) && s[i] <= ' '; i++ {
}
j := i
for ; j < len(s) && s[j] > ' '; j++ {
}
n, err := strconv.ParseInt(s[i:j], 0, 32)
if err != nil {
return 0, s, false
}
for ; j < len(s) && s[j] <= ' '; j++ {
}
return int32(n), s[j:], true
}
// ParseSubfont parses a Plan 9 subfont file.
//
// firstRune is the first rune in the subfont file. For example, the
// Phonetic.6.0 subfont, containing glyphs in the range U+0250 to U+02E9, would
// set firstRune to '\u0250'.
func ParseSubfont(data []byte, firstRune rune) (font.Face, error) {
data, m, err := parseImage(data)
if err != nil {
return nil, err
}
if len(data) < 3*12 {
return nil, errors.New("plan9font: invalid subfont: header too short")
}
n := atoi(data[0*12:])
height := atoi(data[1*12:])
ascent := atoi(data[2*12:])
data = data[3*12:]
if len(data) != 6*(n+1) {
return nil, errors.New("plan9font: invalid subfont: data length mismatch")
}
// Convert from plan9Image to image.Alpha, as the standard library's
// image/draw package works best when glyph masks are of that type.
img := image.NewAlpha(m.Bounds())
for y := img.Rect.Min.Y; y < img.Rect.Max.Y; y++ {
i := img.PixOffset(img.Rect.Min.X, y)
for x := img.Rect.Min.X; x < img.Rect.Max.X; x++ {
img.Pix[i] = m.at(x, y)
i++
}
}
return &subface{
firstRune: firstRune,
n: n,
height: height,
ascent: ascent,
fontchars: parseFontchars(data),
img: img,
}, nil
}
// plan9Image implements that subset of the Plan 9 image feature set that is
// used by this font file format.
//
// Some features, such as the repl bit and a clip rectangle, are omitted for
// simplicity.
type plan9Image struct {
depth int // Depth of the pixels in bits.
width int // Width in bytes of a single scan line.
rect image.Rectangle // Extent of the image.
pix []byte // Pixel bits.
}
func (m *plan9Image) byteoffset(x, y int) int {
a := y * m.width
if m.depth < 8 {
// We need to always round down, but Go rounds toward zero.
np := 8 / m.depth
if x < 0 {
return a + (x-np+1)/np
}
return a + x/np
}
return a + x*(m.depth/8)
}
func (m *plan9Image) Bounds() image.Rectangle { return m.rect }
func (m *plan9Image) ColorModel() color.Model { return color.AlphaModel }
func (m *plan9Image) At(x, y int) color.Color {
if (image.Point{x, y}).In(m.rect) {
return color.Alpha{m.at(x, y)}
}
return color.Alpha{0x00}
}
func (m *plan9Image) at(x, y int) uint8 {
b := m.pix[m.byteoffset(x, y)]
switch m.depth {
case 1:
// CGrey, 1.
mask := uint8(1 << uint8(7-x&7))
if (b & mask) != 0 {
return 0xff
}
return 0
case 2:
// CGrey, 2.
shift := uint(x&3) << 1
// Place pixel at top of word.
y := b << shift
y &= 0xc0
// Replicate throughout.
y |= y >> 2
y |= y >> 4
return y
}
return 0
}
var compressed = []byte("compressed\n")
func parseImage(data []byte) (remainingData []byte, m *plan9Image, retErr error) {
if !bytes.HasPrefix(data, compressed) {
return nil, nil, errors.New("plan9font: unsupported uncompressed format")
}
data = data[len(compressed):]
const hdrSize = 5 * 12
if len(data) < hdrSize {
return nil, nil, errors.New("plan9font: invalid image: header too short")
}
hdr, data := data[:hdrSize], data[hdrSize:]
// Distinguish new channel descriptor from old ldepth. Channel descriptors
// have letters as well as numbers, while ldepths are a single digit
// formatted as %-11d.
new := false
for m := 0; m < 10; m++ {
if hdr[m] != ' ' {
new = true
break
}
}
if hdr[11] != ' ' {
return nil, nil, errors.New("plan9font: invalid image: bad header")
}
if !new {
return nil, nil, errors.New("plan9font: unsupported ldepth format")
}
depth := 0
switch s := strings.TrimSpace(string(hdr[:1*12])); s {
default:
return nil, nil, fmt.Errorf("plan9font: unsupported pixel format %q", s)
case "k1":
depth = 1
case "k2":
depth = 2
}
r := ator(hdr[1*12:])
if r.Min.X > r.Max.X || r.Min.Y > r.Max.Y {
return nil, nil, errors.New("plan9font: invalid image: bad rectangle")
}
width := bytesPerLine(r, depth)
m = &plan9Image{
depth: depth,
width: width,
rect: r,
pix: make([]byte, width*r.Dy()),
}
miny := r.Min.Y
for miny != r.Max.Y {
if len(data) < 2*12 {
return nil, nil, errors.New("plan9font: invalid image: data band too short")
}
maxy := atoi(data[0*12:])
nb := atoi(data[1*12:])
data = data[2*12:]
if len(data) < nb {
return nil, nil, errors.New("plan9font: invalid image: data band length mismatch")
}
buf := data[:nb]
data = data[nb:]
if maxy <= miny || r.Max.Y < maxy {
return nil, nil, fmt.Errorf("plan9font: bad maxy %d", maxy)
}
// An old-format image would flip the bits here, but we don't support
// the old format.
rr := r
rr.Min.Y = miny
rr.Max.Y = maxy
if err := decompress(m, rr, buf); err != nil {
return nil, nil, err
}
miny = maxy
}
return data, m, nil
}
// Compressed data are sequences of byte codes. If the first byte b has the
// 0x80 bit set, the next (b^0x80)+1 bytes are data. Otherwise, these two bytes
// specify a previous string to repeat.
const (
compShortestMatch = 3 // shortest match possible.
compWindowSize = 1024 // window size.
)
var (
errDecompressBufferTooSmall = errors.New("plan9font: decompress: buffer too small")
errDecompressPhaseError = errors.New("plan9font: decompress: phase error")
)
func decompress(m *plan9Image, r image.Rectangle, data []byte) error {
if !r.In(m.rect) {
return errors.New("plan9font: decompress: bad rectangle")
}
bpl := bytesPerLine(r, m.depth)
mem := make([]byte, compWindowSize)
memi := 0
omemi := -1
y := r.Min.Y
linei := m.byteoffset(r.Min.X, y)
eline := linei + bpl
datai := 0
for {
if linei == eline {
y++
if y == r.Max.Y {
break
}
linei = m.byteoffset(r.Min.X, y)
eline = linei + bpl
}
if datai == len(data) {
return errDecompressBufferTooSmall
}
c := data[datai]
datai++
if c >= 128 {
for cnt := c - 128 + 1; cnt != 0; cnt-- {
if datai == len(data) {
return errDecompressBufferTooSmall
}
if linei == eline {
return errDecompressPhaseError
}
m.pix[linei] = data[datai]
linei++
mem[memi] = data[datai]
memi++
datai++
if memi == len(mem) {
memi = 0
}
}
} else {
if datai == len(data) {
return errDecompressBufferTooSmall
}
offs := int(data[datai]) + ((int(c) & 3) << 8) + 1
datai++
if memi < offs {
omemi = memi + (compWindowSize - offs)
} else {
omemi = memi - offs
}
for cnt := (c >> 2) + compShortestMatch; cnt != 0; cnt-- {
if linei == eline {
return errDecompressPhaseError
}
m.pix[linei] = mem[omemi]
linei++
mem[memi] = mem[omemi]
memi++
omemi++
if omemi == len(mem) {
omemi = 0
}
if memi == len(mem) {
memi = 0
}
}
}
}
return nil
}
func ator(b []byte) image.Rectangle {
return image.Rectangle{atop(b), atop(b[2*12:])}
}
func atop(b []byte) image.Point {
return image.Pt(atoi(b), atoi(b[12:]))
}
func atoi(b []byte) int {
i := 0
for ; i < len(b) && b[i] == ' '; i++ {
}
n := 0
for ; i < len(b) && '0' <= b[i] && b[i] <= '9'; i++ {
n = n*10 + int(b[i]) - '0'
}
return n
}
func bytesPerLine(r image.Rectangle, depth int) int {
if depth <= 0 || 32 < depth {
panic("invalid depth")
}
var l int
if r.Min.X >= 0 {
l = (r.Max.X*depth + 7) / 8
l -= (r.Min.X * depth) / 8
} else {
// Make positive before divide.
t := (-r.Min.X*depth + 7) / 8
l = t + (r.Max.X*depth+7)/8
}
return l
}
