Freetype-Go: truetype parser initial check-in.

Parsing a malformed TTF may result in an index out-of-bounds panic,
rather than guaranteeing to return an error. This may be tightened
in the future.

R=r, rsc
CC=golang-dev
http://codereview.appspot.com/940044
This commit is contained in:
Nigel Tao 2010-05-04 09:54:43 +10:00
parent 01b35309ee
commit f6caa104ec
3 changed files with 631 additions and 0 deletions

72
example/truetype/main.go Normal file
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// Copyright 2010 The Freetype-Go Authors. All rights reserved.
// Use of this source code is governed by your choice of either the
// FreeType License or the GNU General Public License version 2,
// both of which can be found in the LICENSE file.
package main
import (
"flag"
"fmt"
"io/ioutil"
"log"
"freetype-go.googlecode.com/hg/freetype/truetype"
)
var fontfile = flag.String("fontfile", "../../luxi-fonts/luxisr.ttf", "filename of the ttf font")
func printBounds(b truetype.Bounds) {
fmt.Printf("XMin:%d YMin:%d XMax:%d YMax:%d\n", b.XMin, b.YMin, b.XMax, b.YMax)
}
func printGlyph(g *truetype.Glyph) {
printBounds(g.B)
fmt.Print("Points:\n---\n")
e := 0
for i, p := range g.Point {
fmt.Printf("%4d, %4d", p.X, p.Y)
if p.Flags&0x01 != 0 {
fmt.Print(" on\n")
} else {
fmt.Print(" off\n")
}
if i+1 == int(g.End[e]) {
fmt.Print("---\n")
e++
}
}
}
func main() {
flag.Parse()
fmt.Printf("Loading fontfile %q\n", *fontfile)
b, err := ioutil.ReadFile(*fontfile)
if err != nil {
log.Stderr(err)
return
}
font, err := truetype.Parse(b)
if err != nil {
log.Stderr(err)
return
}
printBounds(font.Bounds())
fmt.Printf("UnitsPerEm:%d\n\n", font.UnitsPerEm())
c0, c1 := 'A', 'V'
i0 := font.Index(c0)
hm := font.HMetric(i0)
g := truetype.NewGlyph()
err = g.Load(font, i0)
if err != nil {
log.Stderr(err)
return
}
fmt.Printf("'%c' glyph\n", c0)
fmt.Printf("AdvanceWidth:%d LeftSideBearing:%d\n", hm.AdvanceWidth, hm.LeftSideBearing)
printGlyph(g)
i1 := font.Index(c1)
fmt.Printf("\n'%c', '%c' Kerning:%d\n", c0, c1, font.Kerning(i0, i1))
}

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# Copyright 2010 The Freetype-Go Authors. All rights reserved.
# Use of this source code is governed by your choice of either the
# FreeType License or the GNU General Public License version 2,
# both of which can be found in the LICENSE file.
include $(GOROOT)/src/Make.$(GOARCH)
TARG=freetype-go.googlecode.com/hg/freetype/truetype
GOFILES=\
truetype.go\
include $(GOROOT)/src/Make.pkg

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// Copyright 2010 The Freetype-Go Authors. All rights reserved.
// Use of this source code is governed by your choice of either the
// FreeType License or the GNU General Public License version 2,
// both of which can be found in the LICENSE file.
// The truetype package provides a parser for the TTF file format. That format
// is documented at http://developer.apple.com/fonts/TTRefMan/ and
// http://www.microsoft.com/typography/otspec/
//
// All numbers (e.g. bounds, point co-ordinates, font metrics) are measured in
// FUnits. To convert from FUnits to pixels, scale by
// (pointSize * resolution) / (font.UnitsPerEm() * 72dpi)
// For example, 550 FUnits at 18pt, 72dpi and 2048upe is 4.83 pixels.
package truetype
import (
"fmt"
"os"
)
// An Index is a Font's index of a Unicode code point.
type Index uint16
// A Bounds holds the co-ordinate range of one or more glyphs.
// The endpoints are inclusive.
type Bounds struct {
XMin, YMin, XMax, YMax int16
}
// An HMetric holds the horizontal metrics of a single glyph.
type HMetric struct {
AdvanceWidth uint16
LeftSideBearing int16
}
// A FormatError reports that the input is not a valid TrueType font.
type FormatError string
func (e FormatError) String() string {
return "freetype: invalid TrueType format: " + string(e)
}
// An UnsupportedError reports that the input uses a valid but unimplemented
// TrueType feature.
type UnsupportedError string
func (e UnsupportedError) String() string {
return "freetype: unsupported TrueType feature: " + string(e)
}
// data interprets a byte slice as a stream of integer values.
type data []byte
// u32 returns the next big-endian uint32.
func (d *data) u32() uint32 {
x := uint32((*d)[0])<<24 | uint32((*d)[1])<<16 | uint32((*d)[2])<<8 | uint32((*d)[3])
*d = (*d)[4:]
return x
}
// u16 returns the next big-endian uint16.
func (d *data) u16() uint16 {
x := uint16((*d)[0])<<8 | uint16((*d)[1])
*d = (*d)[2:]
return x
}
// u8 returns the next uint8.
func (d *data) u8() uint8 {
x := (*d)[0]
*d = (*d)[1:]
return x
}
// skip skips the next n bytes.
func (d *data) skip(n int) {
*d = (*d)[n:]
}
// readTable returns a slice of the TTF data given by a table's directory entry.
func readTable(ttf []byte, offsetLength []byte) ([]byte, os.Error) {
d := data(offsetLength)
offset := int(d.u32())
if offset < 0 || offset > 1<<24 || offset > len(ttf) {
return nil, FormatError(fmt.Sprintf("offset too large: %d", offset))
}
length := int(d.u32())
if length < 0 || length > 1<<24 || offset+length > len(ttf) {
return nil, FormatError(fmt.Sprintf("length too large: %d", length))
}
return ttf[offset : offset+length], nil
}
const (
locaOffsetFormatUnknown int = iota
locaOffsetFormatShort
locaOffsetFormatLong
)
// A cm holds a parsed cmap entry.
type cm struct {
start, end, delta, offset uint16
}
// A Font represents a Truetype font.
type Font struct {
// Tables sliced from the TTF data. The different tables are documented
// at http://developer.apple.com/fonts/TTRefMan/RM06/Chap6.html
cmap, glyf, head, hhea, hmtx, kern, loca, maxp []byte
cmapIndexes []byte
// Cached values derived from the raw ttf data.
cm []cm
locaOffsetFormat int
nGlyph, nHMetric, nKern int
unitsPerEm int
bounds Bounds
}
func (f *Font) parseCmap() os.Error {
const (
cmapFormat4 = 4
languageIndependent = 0
// A 32-bit encoding consists of a most-significant 16-bit Platform ID and a
// least-significant 16-bit Platform Specific ID.
unicodeEncoding = 0x00000003 // PID = 0 (Unicode), PSID = 3 (Unicode 2.0)
microsoftEncoding = 0x00030001 // PID = 3 (Microsoft), PSID = 1 (UCS-2)
)
if len(f.cmap) < 4 {
return FormatError("cmap too short")
}
d := data(f.cmap[2:])
nsubtab := int(d.u16())
if len(f.cmap) < 8*nsubtab+4 {
return FormatError("cmap too short")
}
offset, found := 0, false
for i := 0; i < nsubtab; i++ {
// We read the 16-bit Platform ID and 16-bit Platform Specific ID as a single uint32.
// All values are big-endian.
pidPsid, o := d.u32(), d.u32()
// We prefer the Unicode cmap encoding. Failing to find that, we fall
// back onto the Microsoft cmap encoding.
if pidPsid == unicodeEncoding {
offset, found = int(o), true
break
} else if pidPsid == microsoftEncoding {
offset, found = int(o), true
// We don't break out of the for loop, so that Unicode can override Microsoft.
}
}
if !found {
return UnsupportedError("cmap encoding")
}
if offset <= 0 || offset > len(f.cmap) {
return FormatError("bad cmap offset")
}
d = data(f.cmap[offset:])
cmapFormat := d.u16()
if cmapFormat != cmapFormat4 {
return UnsupportedError(fmt.Sprintf("cmap format: %d", cmapFormat))
}
d.skip(2)
language := d.u16()
if language != languageIndependent {
return UnsupportedError(fmt.Sprintf("language: %d", language))
}
segCountX2 := int(d.u16())
if segCountX2%2 == 1 {
return FormatError(fmt.Sprintf("bad segCountX2: %d", segCountX2))
}
segCount := segCountX2 / 2
d.skip(6)
f.cm = make([]cm, segCount)
for i := 0; i < segCount; i++ {
f.cm[i].end = d.u16()
}
d.skip(2)
for i := 0; i < segCount; i++ {
f.cm[i].start = d.u16()
}
for i := 0; i < segCount; i++ {
f.cm[i].delta = d.u16()
}
for i := 0; i < segCount; i++ {
f.cm[i].offset = d.u16()
}
f.cmapIndexes = []byte(d)
return nil
}
func (f *Font) parseHead() os.Error {
if len(f.head) != 54 {
return FormatError(fmt.Sprintf("bad head length: %d", len(f.head)))
}
d := data(f.head[18:])
f.unitsPerEm = int(d.u16())
d.skip(16)
f.bounds.XMin = int16(d.u16())
f.bounds.YMin = int16(d.u16())
f.bounds.XMax = int16(d.u16())
f.bounds.YMax = int16(d.u16())
d.skip(6)
switch i := d.u16(); i {
case 0:
f.locaOffsetFormat = locaOffsetFormatShort
case 1:
f.locaOffsetFormat = locaOffsetFormatLong
default:
return FormatError(fmt.Sprintf("bad indexToLocFormat: %d", i))
}
return nil
}
func (f *Font) parseHhea() os.Error {
if len(f.hhea) != 36 {
return FormatError(fmt.Sprintf("bad hhea length: %d", len(f.hhea)))
}
d := data(f.hhea[34:])
f.nHMetric = int(d.u16())
if 4*f.nHMetric+2*(f.nGlyph-f.nHMetric) != len(f.hmtx) {
return FormatError(fmt.Sprintf("bad hmtx length: %d", len(f.hmtx)))
}
return nil
}
func (f *Font) parseKern() os.Error {
// Apple's TrueType documentation (http://developer.apple.com/fonts/TTRefMan/RM06/Chap6kern.html) says:
// "Previous versions of the 'kern' table defined both the version and nTables fields in the header
// as UInt16 values and not UInt32 values. Use of the older format on the Mac OS is discouraged
// (although AAT can sense an old kerning table and still make correct use of it). Microsoft
// Windows still uses the older format for the 'kern' table and will not recognize the newer one.
// Fonts targeted for the Mac OS only should use the new format; fonts targeted for both the Mac OS
// and Windows should use the old format."
// Since we expect that almost all fonts aim to be Windows-compatible, we only parse the "older" format,
// just like the C Freetype implementation.
if len(f.kern) == 0 {
if f.nKern != 0 {
return FormatError("bad kern table length")
}
return nil
}
if len(f.kern) < 18 {
return FormatError("kern data too short")
}
d := data(f.kern[0:])
version := d.u16()
if version != 0 {
return UnsupportedError(fmt.Sprintf("kern version: %d", version))
}
n := d.u16()
if n != 1 {
return UnsupportedError(fmt.Sprintf("kern nTables: %d", n))
}
d.skip(2)
length := int(d.u16())
coverage := d.u16()
if coverage != 0x0001 {
// We only support horizontal kerning.
return UnsupportedError(fmt.Sprintf("kern coverage: 0x%04x", coverage))
}
f.nKern = int(d.u16())
if 6*f.nKern != length-14 {
return FormatError("bad kern table length")
}
return nil
}
func (f *Font) parseMaxp() os.Error {
if len(f.maxp) != 32 {
return FormatError(fmt.Sprintf("bad maxp length: %d", len(f.maxp)))
}
d := data(f.maxp[4:])
f.nGlyph = int(d.u16())
return nil
}
// Bounds returns the union of a Font's glyphs' bounds.
func (f *Font) Bounds() Bounds {
return f.bounds
}
// UnitsPerEm returns the number of FUnits in a Font's em-square.
func (f *Font) UnitsPerEm() int {
return f.unitsPerEm
}
// Index returns a Font's index for the given Unicode code point.
func (f *Font) Index(codePoint int) Index {
c := uint16(codePoint)
n := len(f.cm)
for i := 0; i < n; i++ {
if f.cm[i].start <= c && c <= f.cm[i].end {
if f.cm[i].offset == 0 {
return Index(c + f.cm[i].delta)
}
offset := int(f.cm[i].offset) + 2*(i-n+int(c-f.cm[i].start))
d := data(f.cmapIndexes[offset:])
return Index(d.u16())
}
}
return Index(0)
}
// HMetric returns the horizontal metrics for the glyph with the given index.
func (f *Font) HMetric(i Index) HMetric {
j := int(i)
if j >= f.nGlyph {
return HMetric{}
}
if j >= f.nHMetric {
var hm HMetric
p := 4 * (f.nHMetric - 1)
d := data(f.hmtx[p:])
hm.AdvanceWidth = d.u16()
p += 2*(j-f.nHMetric) + 4
d = data(f.hmtx[p:])
hm.LeftSideBearing = int16(d.u16())
return hm
}
d := data(f.hmtx[4*j:])
return HMetric{d.u16(), int16(d.u16())}
}
// Kerning returns the kerning for the given glyph pair.
func (f *Font) Kerning(i0, i1 Index) int16 {
if f.nKern == 0 {
return 0
}
g := uint32(i0)<<16 | uint32(i1)
lo, hi := 0, f.nKern
for lo < hi {
i := (lo + hi) / 2
d := data(f.kern[18+6*i:])
ig := d.u32()
if ig < g {
lo = i + 1
} else if ig > g {
hi = i
} else {
return int16(d.u16())
}
}
return 0
}
// Parse returns a new Font for the given TTF data.
func Parse(ttf []byte) (font *Font, err os.Error) {
if len(ttf) < 12 {
err = FormatError("TTF data is too short")
return
}
d := data(ttf[0:])
if d.u32() != 0x00010000 {
err = FormatError("bad version")
return
}
n := int(d.u16())
if len(ttf) < 16*n+12 {
err = FormatError("TTF data is too short")
return
}
f := new(Font)
// Assign the table slices.
for i := 0; i < n; i++ {
x := 16*i + 12
switch string(ttf[x : x+4]) {
case "cmap":
f.cmap, err = readTable(ttf, ttf[x+8:x+16])
case "glyf":
f.glyf, err = readTable(ttf, ttf[x+8:x+16])
case "head":
f.head, err = readTable(ttf, ttf[x+8:x+16])
case "hhea":
f.hhea, err = readTable(ttf, ttf[x+8:x+16])
case "hmtx":
f.hmtx, err = readTable(ttf, ttf[x+8:x+16])
case "kern":
f.kern, err = readTable(ttf, ttf[x+8:x+16])
case "loca":
f.loca, err = readTable(ttf, ttf[x+8:x+16])
case "maxp":
f.maxp, err = readTable(ttf, ttf[x+8:x+16])
}
if err != nil {
return
}
}
// Parse and sanity-check the TTF data.
if err = f.parseHead(); err != nil {
return
}
if err = f.parseMaxp(); err != nil {
return
}
if err = f.parseCmap(); err != nil {
return
}
if err = f.parseKern(); err != nil {
return
}
if err = f.parseHhea(); err != nil {
return
}
font = f
return
}
// A Point is a co-ordinate pair plus whether it is ``on'' a contour or an
// ``off'' control point.
type Point struct {
X, Y int16
// The Flags' LSB means whether or not this Point is ``on'' the contour.
// Other bits are reserved for internal use.
Flags uint8
}
// A Glyph holds a glyph's contours. A Glyph can be re-used to load a series
// of glyphs from a Font.
type Glyph struct {
// The glyph's bounding box.
B Bounds
// Point contains all Points from all contours of the glyph.
Point []Point
// The length of End is the number of contours in the glyph. The i'th
// contour consists of points Point[End[i-1]:End[i]], where End[-1]
// is interpreted to mean zero.
End []int
}
// decodeFlags decodes a glyph's run-length encoded flags,
// and returns the remaining data.
func (g *Glyph) decodeFlags(d data) data {
for i := 0; i < len(g.Point); {
c := d.u8()
g.Point[i].Flags = c
i++
if c&0x08 != 0 {
count := d.u8()
for ; count > 0; count-- {
g.Point[i].Flags = c
i++
}
}
}
return d
}
// decodeCoords decodes a glyph's delta encoded co-ordinates.
func (g *Glyph) decodeCoords(d data) {
var x int16
for i := 0; i < len(g.Point); i++ {
f := g.Point[i].Flags
if f&0x02 != 0 {
dx := int16(d.u8())
if f&0x10 == 0 {
x -= dx
} else {
x += dx
}
} else if f&0x10 == 0 {
x += int16(d.u16())
}
g.Point[i].X = x
}
var y int16
for i := 0; i < len(g.Point); i++ {
f := g.Point[i].Flags
if f&0x04 != 0 {
dy := int16(d.u8())
if f&0x20 == 0 {
y -= dy
} else {
y += dy
}
} else if f&0x20 == 0 {
y += int16(d.u16())
}
g.Point[i].Y = y
}
}
// Load loads a glyph's contours from a Font, overwriting any previously
// loaded contours for this Glyph.
func (g *Glyph) Load(f *Font, i Index) os.Error {
// Reset the Glyph.
g.B = Bounds{}
g.Point = g.Point[0:0]
g.End = g.End[0:0]
// Find the relevant slice of f.glyf.
var g0, g1 uint32
if f.locaOffsetFormat == locaOffsetFormatShort {
d := data(f.loca[2*i:])
g0 = 2 * uint32(d.u16())
g1 = 2 * uint32(d.u16())
} else {
d := data(f.loca[4*i:])
g0 = d.u32()
g1 = d.u32()
}
if g0 == g1 {
return nil
}
d := data(f.glyf[g0:g1])
// Decode the contour end indices.
ne := int(d.u16())
if ne == 1<<16-1 {
return UnsupportedError("compound glyph")
}
g.B.XMin = int16(d.u16())
g.B.YMin = int16(d.u16())
g.B.XMax = int16(d.u16())
g.B.YMax = int16(d.u16())
if ne <= cap(g.End) {
g.End = g.End[0:ne]
} else {
g.End = make([]int, ne, ne*2)
}
for i := 0; i < ne; i++ {
g.End[i] = 1 + int(d.u16())
}
// Skip the TrueType hinting instructions.
instrLen := int(d.u16())
d.skip(instrLen)
// Decode the points.
np := int(g.End[ne-1])
if np <= cap(g.Point) {
g.Point = g.Point[0:np]
} else {
g.Point = make([]Point, np, np*2)
}
d = g.decodeFlags(d)
g.decodeCoords(d)
return nil
}
// NewGlyph returns a newly allocated Glyph.
func NewGlyph() *Glyph {
g := new(Glyph)
g.Point = make([]Point, 0, 256)
g.End = make([]int, 0, 32)
return g
}