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// Copyright 2016 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 sfnt implements a decoder for SFNT font file formats, including
// TrueType and OpenType.
package sfnt // import "golang.org/x/image/font/sfnt"
// This implementation was written primarily to the
// https://www.microsoft.com/en-us/Typography/OpenTypeSpecification.aspx
// specification. Additional documentation is at
// http://developer.apple.com/fonts/TTRefMan/
//
// The pyftinspect tool from https://github.com/fonttools/fonttools is useful
// for inspecting SFNT fonts.
//
// The ttfdump tool is also useful. For example:
// ttfdump -t cmap ../testdata/CFFTest.otf dump.txt
import (
"errors"
"io"
"golang.org/x/image/math/fixed"
"golang.org/x/text/encoding/charmap"
)
// These constants are not part of the specifications, but are limitations used
// by this implementation.
const (
// This value is arbitrary, but defends against parsing malicious font
// files causing excessive memory allocations. For reference, Adobe's
// SourceHanSansSC-Regular.otf has 65535 glyphs and:
// - its format-4 cmap table has 1581 segments.
// - its format-12 cmap table has 16498 segments.
//
// TODO: eliminate this constraint? If the cmap table is very large, load
// some or all of it lazily (at the time Font.GlyphIndex is called) instead
// of all of it eagerly (at the time Font.initialize is called), while
// keeping an upper bound on the memory used? This will make the code in
// cmap.go more complicated, considering that all of the Font methods are
// safe to call concurrently, as long as each call has a different *Buffer.
maxCmapSegments = 20000
maxGlyphDataLength = 64 * 1024
maxHintBits = 256
maxNumTables = 256
maxRealNumberStrLen = 64 // Maximum length in bytes of the "-123.456E-7" representation.
// (maxTableOffset + maxTableLength) will not overflow an int32.
maxTableLength = 1 << 29
maxTableOffset = 1 << 29
)
var (
// ErrNotFound indicates that the requested value was not found.
ErrNotFound = errors.New("sfnt: not found")
errInvalidBounds = errors.New("sfnt: invalid bounds")
errInvalidCFFTable = errors.New("sfnt: invalid CFF table")
errInvalidCmapTable = errors.New("sfnt: invalid cmap table")
errInvalidGlyphData = errors.New("sfnt: invalid glyph data")
errInvalidHeadTable = errors.New("sfnt: invalid head table")
errInvalidLocaTable = errors.New("sfnt: invalid loca table")
errInvalidLocationData = errors.New("sfnt: invalid location data")
errInvalidMaxpTable = errors.New("sfnt: invalid maxp table")
errInvalidNameTable = errors.New("sfnt: invalid name table")
errInvalidSourceData = errors.New("sfnt: invalid source data")
errInvalidTableOffset = errors.New("sfnt: invalid table offset")
errInvalidTableTagOrder = errors.New("sfnt: invalid table tag order")
errInvalidUCS2String = errors.New("sfnt: invalid UCS-2 string")
errInvalidVersion = errors.New("sfnt: invalid version")
errUnsupportedCFFVersion = errors.New("sfnt: unsupported CFF version")
errUnsupportedCmapEncodings = errors.New("sfnt: unsupported cmap encodings")
errUnsupportedCmapFormat = errors.New("sfnt: unsupported cmap format")
errUnsupportedCompoundGlyph = errors.New("sfnt: unsupported compound glyph")
errUnsupportedGlyphDataLength = errors.New("sfnt: unsupported glyph data length")
errUnsupportedRealNumberEncoding = errors.New("sfnt: unsupported real number encoding")
errUnsupportedNumberOfCmapSegments = errors.New("sfnt: unsupported number of cmap segments")
errUnsupportedNumberOfHints = errors.New("sfnt: unsupported number of hints")
errUnsupportedNumberOfTables = errors.New("sfnt: unsupported number of tables")
errUnsupportedPlatformEncoding = errors.New("sfnt: unsupported platform encoding")
errUnsupportedTableOffsetLength = errors.New("sfnt: unsupported table offset or length")
errUnsupportedType2Charstring = errors.New("sfnt: unsupported Type 2 Charstring")
)
// GlyphIndex is a glyph index in a Font.
type GlyphIndex uint16
// NameID identifies a name table entry.
//
// See the "Name IDs" section of
// https://www.microsoft.com/typography/otspec/name.htm
type NameID uint16
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
)
// 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).
type Units int32
func u16(b []byte) uint16 {
_ = b[1] // Bounds check hint to compiler.
return uint16(b[0])<<8 | uint16(b[1])<<0
}
func u32(b []byte) uint32 {
_ = b[3] // Bounds check hint to compiler.
return uint32(b[0])<<24 | uint32(b[1])<<16 | uint32(b[2])<<8 | uint32(b[3])<<0
}
// source is a source of byte data. Conceptually, it is like an io.ReaderAt,
// except that a common source of SFNT font data is in-memory instead of
// on-disk: a []byte containing the entire data, either as a global variable
// (e.g. "goregular.TTF") or the result of an ioutil.ReadFile call. In such
// cases, as an optimization, we skip the io.Reader / io.ReaderAt model of
// copying from the source to a caller-supplied buffer, and instead provide
// direct access to the underlying []byte data.
type source struct {
b []byte
r io.ReaderAt
// TODO: add a caching layer, if we're using the io.ReaderAt? Note that
// this might make a source no longer safe to use concurrently.
}
// valid returns whether exactly one of s.b and s.r is nil.
func (s *source) valid() bool {
return (s.b == nil) != (s.r == nil)
}
// viewBufferWritable returns whether the []byte returned by source.view can be
// written to by the caller, including by passing it to the same method
// (source.view) on other receivers (i.e. different sources).
//
// In other words, it returns whether the source's underlying data is an
// io.ReaderAt, not a []byte.
func (s *source) viewBufferWritable() bool {
return s.b == nil
}
// view returns the length bytes at the given offset. buf is an optional
// scratch buffer to reduce allocations when calling view multiple times. A nil
// buf is valid. The []byte returned may be a sub-slice of buf[:cap(buf)], or
// it may be an unrelated slice. In any case, the caller should not modify the
// contents of the returned []byte, other than passing that []byte back to this
// method on the same source s.
func (s *source) view(buf []byte, offset, length int) ([]byte, error) {
if 0 > offset || offset > offset+length {
return nil, errInvalidBounds
}
// Try reading from the []byte.
if s.b != nil {
if offset+length > len(s.b) {
return nil, errInvalidBounds
}
return s.b[offset : offset+length], nil
}
// Read from the io.ReaderAt.
if length <= cap(buf) {
buf = buf[:length]
} else {
// Round length up to the nearest KiB. The slack can lead to fewer
// allocations if the buffer is re-used for multiple source.view calls.
n := length
n += 1023
n &^= 1023
buf = make([]byte, length, n)
}
if n, err := s.r.ReadAt(buf, int64(offset)); n != length {
return nil, err
}
return buf, nil
}
// u16 returns the uint16 in the table t at the relative offset i.
//
// buf is an optional scratch buffer as per the source.view method.
func (s *source) u16(buf []byte, t table, i int) (uint16, error) {
if i < 0 || uint(t.length) < uint(i+2) {
return 0, errInvalidBounds
}
buf, err := s.view(buf, int(t.offset)+i, 2)
if err != nil {
return 0, err
}
return u16(buf), nil
}
// table is a section of the font data.
type table struct {
offset, length uint32
}
// Parse parses an SFNT font from a []byte data source.
func Parse(src []byte) (*Font, error) {
f := &Font{src: source{b: src}}
if err := f.initialize(); err != nil {
return nil, err
}
return f, nil
}
// ParseReaderAt parses an SFNT font from an io.ReaderAt data source.
func ParseReaderAt(src io.ReaderAt) (*Font, error) {
f := &Font{src: source{r: src}}
if err := f.initialize(); err != nil {
return nil, err
}
return f, nil
}
// 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.
type Font struct {
src source
// https://www.microsoft.com/typography/otspec/otff.htm#otttables
// "Required Tables".
cmap table
head table
hhea table
hmtx table
maxp table
name table
os2 table
post table
// https://www.microsoft.com/typography/otspec/otff.htm#otttables
// "Tables Related to TrueType Outlines".
//
// This implementation does not support hinting, so it does not read the
// cvt, fpgm gasp or prep tables.
glyf table
loca table
// https://www.microsoft.com/typography/otspec/otff.htm#otttables
// "Tables Related to PostScript Outlines".
//
// TODO: cff2, vorg?
cff table
// https://www.microsoft.com/typography/otspec/otff.htm#otttables
// "Advanced Typographic Tables".
//
// TODO: base, gdef, gpos, gsub, jstf, math?
// https://www.microsoft.com/typography/otspec/otff.htm#otttables
// "Other OpenType Tables".
//
// TODO: hdmx, kern, vmtx? Others?
cached struct {
glyphIndex func(f *Font, b *Buffer, r rune) (GlyphIndex, error)
indexToLocFormat bool // false means short, true means long.
isPostScript bool
unitsPerEm Units
// The glyph data for the glyph index i is in
// src[locations[i+0]:locations[i+1]].
locations []uint32
}
}
// NumGlyphs returns the number of glyphs in f.
func (f *Font) NumGlyphs() int { return len(f.cached.locations) - 1 }
// UnitsPerEm returns the number of units per em for f.
func (f *Font) UnitsPerEm() Units { return f.cached.unitsPerEm }
func (f *Font) initialize() error {
if !f.src.valid() {
return errInvalidSourceData
}
buf, err := f.initializeTables(nil)
if err != nil {
return err
}
buf, err = f.parseHead(buf)
if err != nil {
return err
}
buf, err = f.parseMaxp(buf)
if err != nil {
return err
}
buf, err = f.parseCmap(buf)
if err != nil {
return err
}
return nil
}
func (f *Font) initializeTables(buf []byte) ([]byte, error) {
// https://www.microsoft.com/typography/otspec/otff.htm "Organization of an
// OpenType Font" says that "The OpenType font starts with the Offset
// Table", which is 12 bytes.
buf, err := f.src.view(buf, 0, 12)
if err != nil {
return nil, err
}
switch u32(buf) {
default:
return nil, errInvalidVersion
case 0x00010000:
// No-op.
case 0x4f54544f: // "OTTO".
f.cached.isPostScript = true
}
numTables := int(u16(buf[4:]))
if numTables > maxNumTables {
return nil, errUnsupportedNumberOfTables
}
// "The Offset Table is followed immediately by the Table Record entries...
// sorted in ascending order by tag", 16 bytes each.
buf, err = f.src.view(buf, 12, 16*numTables)
if err != nil {
return nil, err
}
for b, first, prevTag := buf, true, uint32(0); len(b) > 0; b = b[16:] {
tag := u32(b)
if first {
first = false
} else if tag <= prevTag {
return nil, errInvalidTableTagOrder
}
prevTag = tag
o, n := u32(b[8:12]), u32(b[12:16])
if o > maxTableOffset || n > maxTableLength {
return nil, errUnsupportedTableOffsetLength
}
// We ignore the checksums, but "all tables must begin on four byte
// boundries [sic]".
if o&3 != 0 {
return nil, errInvalidTableOffset
}
// Match the 4-byte tag as a uint32. For example, "OS/2" is 0x4f532f32.
switch tag {
case 0x43464620:
f.cff = table{o, n}
case 0x4f532f32:
f.os2 = table{o, n}
case 0x636d6170:
f.cmap = table{o, n}
case 0x676c7966:
f.glyf = table{o, n}
case 0x68656164:
f.head = table{o, n}
case 0x68686561:
f.hhea = table{o, n}
case 0x686d7478:
f.hmtx = table{o, n}
case 0x6c6f6361:
f.loca = table{o, n}
case 0x6d617870:
f.maxp = table{o, n}
case 0x6e616d65:
f.name = table{o, n}
case 0x706f7374:
f.post = table{o, n}
}
}
return buf, nil
}
func (f *Font) parseCmap(buf []byte) ([]byte, error) {
// https://www.microsoft.com/typography/OTSPEC/cmap.htm
const headerSize, entrySize = 4, 8
if f.cmap.length < headerSize {
return nil, errInvalidCmapTable
}
u, err := f.src.u16(buf, f.cmap, 2)
if err != nil {
return nil, err
}
numSubtables := int(u)
if f.cmap.length < headerSize+entrySize*uint32(numSubtables) {
return nil, errInvalidCmapTable
}
var (
bestWidth int
bestOffset uint32
bestLength uint32
bestFormat uint16
)
// Scan all of the subtables, picking the widest supported one. See the
// platformEncodingWidth comment for more discussion of width.
for i := 0; i < numSubtables; i++ {
buf, err = f.src.view(buf, int(f.cmap.offset)+headerSize+entrySize*i, entrySize)
if err != nil {
return nil, err
}
pid := u16(buf)
psid := u16(buf[2:])
width := platformEncodingWidth(pid, psid)
if width <= bestWidth {
continue
}
offset := u32(buf[4:])
if offset > f.cmap.length-4 {
return nil, errInvalidCmapTable
}
buf, err = f.src.view(buf, int(f.cmap.offset+offset), 4)
if err != nil {
return nil, err
}
format := u16(buf)
if !supportedCmapFormat(format, pid, psid) {
continue
}
length := uint32(u16(buf[2:]))
bestWidth = width
bestOffset = offset
bestLength = length
bestFormat = format
}
if bestWidth == 0 {
return nil, errUnsupportedCmapEncodings
}
return f.makeCachedGlyphIndex(buf, bestOffset, bestLength, bestFormat)
}
func (f *Font) parseHead(buf []byte) ([]byte, error) {
// https://www.microsoft.com/typography/otspec/head.htm
if f.head.length != 54 {
return nil, errInvalidHeadTable
}
u, err := f.src.u16(buf, f.head, 18)
if err != nil {
return nil, err
}
if u == 0 {
return nil, errInvalidHeadTable
}
f.cached.unitsPerEm = Units(u)
u, err = f.src.u16(buf, f.head, 50)
if err != nil {
return nil, err
}
f.cached.indexToLocFormat = u != 0
return buf, nil
}
func (f *Font) parseMaxp(buf []byte) ([]byte, error) {
// https://www.microsoft.com/typography/otspec/maxp.htm
if f.cached.isPostScript {
if f.maxp.length != 6 {
return nil, errInvalidMaxpTable
}
} else {
if f.maxp.length != 32 {
return nil, errInvalidMaxpTable
}
}
u, err := f.src.u16(buf, f.maxp, 4)
if err != nil {
return nil, err
}
numGlyphs := int(u)
if f.cached.isPostScript {
p := cffParser{
src: &f.src,
base: int(f.cff.offset),
offset: int(f.cff.offset),
end: int(f.cff.offset + f.cff.length),
}
f.cached.locations, err = p.parse()
if err != nil {
return nil, err
}
} else {
f.cached.locations, err = parseLoca(
&f.src, f.loca, f.glyf.offset, f.cached.indexToLocFormat, numGlyphs)
if err != nil {
return nil, err
}
}
if len(f.cached.locations) != numGlyphs+1 {
return nil, errInvalidLocationData
}
return buf, nil
}
// TODO: API for looking up glyph variants?? For example, some fonts may
// provide both slashed and dotted zero glyphs ('0'), or regular and 'old
// style' numerals, and users can direct software to choose a variant.
// 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 (f *Font) GlyphIndex(b *Buffer, r rune) (GlyphIndex, error) {
return f.cached.glyphIndex(f, b, r)
}
func (f *Font) viewGlyphData(b *Buffer, x GlyphIndex) ([]byte, error) {
xx := int(x)
if f.NumGlyphs() <= xx {
return nil, ErrNotFound
}
i := f.cached.locations[xx+0]
j := f.cached.locations[xx+1]
if j-i > maxGlyphDataLength {
return nil, errUnsupportedGlyphDataLength
}
return b.view(&f.src, int(i), int(j-i))
}
// LoadGlyphOptions are the options to the Font.LoadGlyph method.
type LoadGlyphOptions struct {
// TODO: scale / transform / hinting.
}
// LoadGlyph returns the vector segments for the x'th glyph.
//
// If b is non-nil, the segments become invalid to use once b is re-used.
//
// It returns ErrNotFound if the glyph index is out of range.
func (f *Font) LoadGlyph(b *Buffer, x GlyphIndex, opts *LoadGlyphOptions) ([]Segment, error) {
if b == nil {
b = &Buffer{}
}
buf, err := f.viewGlyphData(b, x)
if err != nil {
return nil, err
}
b.segments = b.segments[:0]
if f.cached.isPostScript {
b.psi.type2Charstrings.initialize(b.segments)
if err := b.psi.run(psContextType2Charstring, buf); err != nil {
return nil, err
}
b.segments = b.psi.type2Charstrings.segments
} else {
segments, err := appendGlyfSegments(b.segments, buf)
if err != nil {
return nil, err
}
b.segments = segments
}
// TODO: look at opts to scale / transform / hint the Buffer.segments.
return b.segments, nil
}
// Name returns the name value keyed by the given NameID.
//
// It returns ErrNotFound if there is no value for that key.
func (f *Font) Name(b *Buffer, id NameID) (string, error) {
if b == nil {
b = &Buffer{}
}
const headerSize, entrySize = 6, 12
if f.name.length < headerSize {
return "", errInvalidNameTable
}
buf, err := b.view(&f.src, int(f.name.offset), headerSize)
if err != nil {
return "", err
}
numSubtables := u16(buf[2:])
if f.name.length < headerSize+entrySize*uint32(numSubtables) {
return "", errInvalidNameTable
}
stringOffset := u16(buf[4:])
seen := false
for i, n := 0, int(numSubtables); i < n; i++ {
buf, err := b.view(&f.src, int(f.name.offset)+headerSize+entrySize*i, entrySize)
if err != nil {
return "", err
}
if u16(buf[6:]) != uint16(id) {
continue
}
seen = true
var stringify func([]byte) (string, error)
switch u32(buf) {
default:
continue
case pidMacintosh<<16 | psidMacintoshRoman:
stringify = stringifyMacintosh
case pidWindows<<16 | psidWindowsUCS2:
stringify = stringifyUCS2
}
nameLength := u16(buf[8:])
nameOffset := u16(buf[10:])
buf, err = b.view(&f.src, int(f.name.offset)+int(nameOffset)+int(stringOffset), int(nameLength))
if err != nil {
return "", err
}
return stringify(buf)
}
if seen {
return "", errUnsupportedPlatformEncoding
}
return "", ErrNotFound
}
func stringifyMacintosh(b []byte) (string, error) {
for _, c := range b {
if c >= 0x80 {
// b contains some non-ASCII bytes.
s, _ := charmap.Macintosh.NewDecoder().Bytes(b)
return string(s), nil
}
}
// b contains only ASCII bytes.
return string(b), nil
}
func stringifyUCS2(b []byte) (string, error) {
if len(b)&1 != 0 {
return "", errInvalidUCS2String
}
r := make([]rune, len(b)/2)
for i := range r {
r[i] = rune(u16(b))
b = b[2:]
}
return string(r), nil
}
// 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 Buffer struct {
// buf is a byte buffer for when a Font's source is an io.ReaderAt.
buf []byte
// segments holds glyph vector path segments.
segments []Segment
// psi is a PostScript interpreter for when the Font is an OpenType/CFF
// font.
psi psInterpreter
}
func (b *Buffer) view(src *source, offset, length int) ([]byte, error) {
buf, err := src.view(b.buf, offset, length)
if err != nil {
return nil, err
}
// Only update b.buf if it is safe to re-use buf.
if src.viewBufferWritable() {
b.buf = buf
}
return buf, nil
}
// Segment is a segment of a vector path.
type Segment struct {
Op SegmentOp
Args [6]fixed.Int26_6
}
// SegmentOp is a vector path segment's operator.
type SegmentOp uint32
const (
SegmentOpMoveTo SegmentOp = iota
SegmentOpLineTo
SegmentOpQuadTo
SegmentOpCubeTo
)