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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 (or
// any later version), both of which can be found in the LICENSE file.
// Package truetype provides a parser for the TTF and TTC file formats.
// Those formats are documented at http://developer.apple.com/fonts/TTRefMan/
// and http://www.microsoft.com/typography/otspec/
//
// Some of a font's methods provide lengths or co-ordinates, e.g. bounds, font
// metrics and control points. All these methods take a scale 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 scale is fixed.I(10), which is equal to
// fixed.Int26_6(10 << 6).
//
// To measure a TrueType font in ideal FUnit space, use scale equal to
// font.FUnitsPerEm().
package truetype // import "github.com/golang/freetype/truetype"
import (
"fmt"
"golang.org/x/image/math/fixed"
)
// An Index is a Font's index of a rune.
type Index uint16
// A NameID identifies a name table entry.
//
// See https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6name.html
type NameID uint16
const (
NameIDCopyright NameID = 0
NameIDFontFamily = 1
NameIDFontSubfamily = 2
NameIDUniqueSubfamilyID = 3
NameIDFontFullName = 4
NameIDNameTableVersion = 5
NameIDPostscriptName = 6
NameIDTrademarkNotice = 7
NameIDManufacturerName = 8
NameIDDesignerName = 9
NameIDFontDescription = 10
NameIDFontVendorURL = 11
NameIDFontDesignerURL = 12
NameIDFontLicense = 13
NameIDFontLicenseURL = 14
NameIDPreferredFamily = 16
NameIDPreferredSubfamily = 17
NameIDCompatibleName = 18
NameIDSampleText = 19
)
const (
// A 32-bit encoding consists of a most-significant 16-bit Platform ID and a
// least-significant 16-bit Platform Specific ID. The magic numbers are
// specified at https://www.microsoft.com/typography/otspec/name.htm
unicodeEncodingBMPOnly = 0x00000003 // PID = 0 (Unicode), PSID = 3 (Unicode 2.0 BMP Only)
unicodeEncodingFull = 0x00000004 // PID = 0 (Unicode), PSID = 4 (Unicode 2.0 Full Repertoire)
microsoftSymbolEncoding = 0x00030000 // PID = 3 (Microsoft), PSID = 0 (Symbol)
microsoftUCS2Encoding = 0x00030001 // PID = 3 (Microsoft), PSID = 1 (UCS-2)
microsoftUCS4Encoding = 0x0003000a // PID = 3 (Microsoft), PSID = 10 (UCS-4)
)
// An HMetric holds the horizontal metrics of a single glyph.
type HMetric struct {
AdvanceWidth, LeftSideBearing fixed.Int26_6
}
// A VMetric holds the vertical metrics of a single glyph.
type VMetric struct {
AdvanceHeight, TopSideBearing fixed.Int26_6
}
// A FormatError reports that the input is not a valid TrueType font.
type FormatError string
func (e FormatError) Error() 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) Error() string {
return "freetype: unsupported TrueType feature: " + string(e)
}
// u32 returns the big-endian uint32 at b[i:].
func u32(b []byte, i int) uint32 {
return uint32(b[i])<<24 | uint32(b[i+1])<<16 | uint32(b[i+2])<<8 | uint32(b[i+3])
}
// u16 returns the big-endian uint16 at b[i:].
func u16(b []byte, i int) uint16 {
return uint16(b[i])<<8 | uint16(b[i+1])
}
// readTable returns a slice of the TTF data given by a table's directory entry.
func readTable(ttf []byte, offsetLength []byte) ([]byte, error) {
offset := int(u32(offsetLength, 0))
if offset < 0 {
return nil, FormatError(fmt.Sprintf("offset too large: %d", uint32(offset)))
}
length := int(u32(offsetLength, 4))
if length < 0 {
return nil, FormatError(fmt.Sprintf("length too large: %d", uint32(length)))
}
end := offset + length
if end < 0 || end > len(ttf) {
return nil, FormatError(fmt.Sprintf("offset + length too large: %d", uint32(offset)+uint32(length)))
}
return ttf[offset:end], nil
}
// parseSubtables returns the offset and platformID of the best subtable in
// table, where best favors a Unicode cmap encoding, and failing that, a
// Microsoft cmap encoding. offset is the offset of the first subtable in
// table, and size is the size of each subtable.
//
// If pred is non-nil, then only subtables that satisfy that predicate will be
// considered.
func parseSubtables(table []byte, name string, offset, size int, pred func([]byte) bool) (
bestOffset int, bestPID uint32, retErr error) {
if len(table) < 4 {
return 0, 0, FormatError(name + " too short")
}
nSubtables := int(u16(table, 2))
if len(table) < size*nSubtables+offset {
return 0, 0, FormatError(name + " too short")
}
ok := false
for i := 0; i < nSubtables; i, offset = i+1, offset+size {
if pred != nil && !pred(table[offset:]) {
continue
}
// We read the 16-bit Platform ID and 16-bit Platform Specific ID as a single uint32.
// All values are big-endian.
pidPsid := u32(table, offset)
// We prefer the Unicode cmap encoding. Failing to find that, we fall
// back onto the Microsoft cmap encoding.
if pidPsid == unicodeEncodingBMPOnly || pidPsid == unicodeEncodingFull {
bestOffset, bestPID, ok = offset, pidPsid>>16, true
break
} else if pidPsid == microsoftSymbolEncoding ||
pidPsid == microsoftUCS2Encoding ||
pidPsid == microsoftUCS4Encoding {
bestOffset, bestPID, ok = offset, pidPsid>>16, true
// We don't break out of the for loop, so that Unicode can override Microsoft.
}
}
if !ok {
return 0, 0, UnsupportedError(name + " encoding")
}
return bestOffset, bestPID, nil
}
const (
locaOffsetFormatUnknown int = iota
locaOffsetFormatShort
locaOffsetFormatLong
)
// A cm holds a parsed cmap entry.
type cm struct {
start, end, delta, offset uint32
}
// 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, cvt, fpgm, glyf, hdmx, head, hhea, hmtx, kern, loca, maxp, name, os2, prep, vmtx []byte
cmapIndexes []byte
// Cached values derived from the raw ttf data.
cm []cm
locaOffsetFormat int
nGlyph, nHMetric, nKern int
fUnitsPerEm int32
ascent int32 // In FUnits.
descent int32 // In FUnits; typically negative.
bounds fixed.Rectangle26_6 // In FUnits.
// Values from the maxp section.
maxTwilightPoints, maxStorage, maxFunctionDefs, maxStackElements uint16
}
func (f *Font) parseCmap() error {
const (
cmapFormat4 = 4
cmapFormat12 = 12
languageIndependent = 0
)
offset, _, err := parseSubtables(f.cmap, "cmap", 4, 8, nil)
if err != nil {
return err
}
offset = int(u32(f.cmap, offset+4))
if offset <= 0 || offset > len(f.cmap) {
return FormatError("bad cmap offset")
}
cmapFormat := u16(f.cmap, offset)
switch cmapFormat {
case cmapFormat4:
language := u16(f.cmap, offset+4)
if language != languageIndependent {
return UnsupportedError(fmt.Sprintf("language: %d", language))
}
segCountX2 := int(u16(f.cmap, offset+6))
if segCountX2%2 == 1 {
return FormatError(fmt.Sprintf("bad segCountX2: %d", segCountX2))
}
segCount := segCountX2 / 2
offset += 14
f.cm = make([]cm, segCount)
for i := 0; i < segCount; i++ {
f.cm[i].end = uint32(u16(f.cmap, offset))
offset += 2
}
offset += 2
for i := 0; i < segCount; i++ {
f.cm[i].start = uint32(u16(f.cmap, offset))
offset += 2
}
for i := 0; i < segCount; i++ {
f.cm[i].delta = uint32(u16(f.cmap, offset))
offset += 2
}
for i := 0; i < segCount; i++ {
f.cm[i].offset = uint32(u16(f.cmap, offset))
offset += 2
}
f.cmapIndexes = f.cmap[offset:]
return nil
case cmapFormat12:
if u16(f.cmap, offset+2) != 0 {
return FormatError(fmt.Sprintf("cmap format: % x", f.cmap[offset:offset+4]))
}
length := u32(f.cmap, offset+4)
language := u32(f.cmap, offset+8)
if language != languageIndependent {
return UnsupportedError(fmt.Sprintf("language: %d", language))
}
nGroups := u32(f.cmap, offset+12)
if length != 12*nGroups+16 {
return FormatError("inconsistent cmap length")
}
offset += 16
f.cm = make([]cm, nGroups)
for i := uint32(0); i < nGroups; i++ {
f.cm[i].start = u32(f.cmap, offset+0)
f.cm[i].end = u32(f.cmap, offset+4)
f.cm[i].delta = u32(f.cmap, offset+8) - f.cm[i].start
offset += 12
}
return nil
}
return UnsupportedError(fmt.Sprintf("cmap format: %d", cmapFormat))
}
func (f *Font) parseHead() error {
if len(f.head) != 54 {
return FormatError(fmt.Sprintf("bad head length: %d", len(f.head)))
}
f.fUnitsPerEm = int32(u16(f.head, 18))
f.bounds.Min.X = fixed.Int26_6(int16(u16(f.head, 36)))
f.bounds.Min.Y = fixed.Int26_6(int16(u16(f.head, 38)))
f.bounds.Max.X = fixed.Int26_6(int16(u16(f.head, 40)))
f.bounds.Max.Y = fixed.Int26_6(int16(u16(f.head, 42)))
switch i := u16(f.head, 50); 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() error {
if len(f.hhea) != 36 {
return FormatError(fmt.Sprintf("bad hhea length: %d", len(f.hhea)))
}
f.ascent = int32(int16(u16(f.hhea, 4)))
f.descent = int32(int16(u16(f.hhea, 6)))
f.nHMetric = int(u16(f.hhea, 34))
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() 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")
}
version, offset := u16(f.kern, 0), 2
if version != 0 {
return UnsupportedError(fmt.Sprintf("kern version: %d", version))
}
n, offset := u16(f.kern, offset), offset+2
if n == 0 {
return UnsupportedError("kern nTables: 0")
}
// TODO: support multiple subtables. In practice, almost all .ttf files
// have only one subtable, if they have a kern table at all. But it's not
// impossible. Xolonium Regular (https://fontlibrary.org/en/font/xolonium)
// has 3 subtables. Those subtables appear to be disjoint, rather than
// being the same kerning pairs encoded in three different ways.
//
// For now, we'll use only the first subtable.
offset += 2 // Skip the version.
length, offset := int(u16(f.kern, offset)), offset+2
coverage, offset := u16(f.kern, offset), offset+2
if coverage != 0x0001 {
// We only support horizontal kerning.
return UnsupportedError(fmt.Sprintf("kern coverage: 0x%04x", coverage))
}
f.nKern, offset = int(u16(f.kern, offset)), offset+2
if 6*f.nKern != length-14 {
return FormatError("bad kern table length")
}
return nil
}
func (f *Font) parseMaxp() error {
if len(f.maxp) != 32 {
return FormatError(fmt.Sprintf("bad maxp length: %d", len(f.maxp)))
}
f.nGlyph = int(u16(f.maxp, 4))
f.maxTwilightPoints = u16(f.maxp, 16)
f.maxStorage = u16(f.maxp, 18)
f.maxFunctionDefs = u16(f.maxp, 20)
f.maxStackElements = u16(f.maxp, 24)
return nil
}
// scale returns x divided by f.fUnitsPerEm, rounded to the nearest integer.
func (f *Font) scale(x fixed.Int26_6) fixed.Int26_6 {
if x >= 0 {
x += fixed.Int26_6(f.fUnitsPerEm) / 2
} else {
x -= fixed.Int26_6(f.fUnitsPerEm) / 2
}
return x / fixed.Int26_6(f.fUnitsPerEm)
}
// Bounds returns the union of a Font's glyphs' bounds.
func (f *Font) Bounds(scale fixed.Int26_6) fixed.Rectangle26_6 {
b := f.bounds
b.Min.X = f.scale(scale * b.Min.X)
b.Min.Y = f.scale(scale * b.Min.Y)
b.Max.X = f.scale(scale * b.Max.X)
b.Max.Y = f.scale(scale * b.Max.Y)
return b
}
// FUnitsPerEm returns the number of FUnits in a Font's em-square's side.
func (f *Font) FUnitsPerEm() int32 {
return f.fUnitsPerEm
}
// Index returns a Font's index for the given rune.
func (f *Font) Index(x rune) Index {
c := uint32(x)
for i, j := 0, len(f.cm); i < j; {
h := i + (j-i)/2
cm := &f.cm[h]
if c < cm.start {
j = h
} else if cm.end < c {
i = h + 1
} else if cm.offset == 0 {
return Index(c + cm.delta)
} else {
offset := int(cm.offset) + 2*(h-len(f.cm)+int(c-cm.start))
return Index(u16(f.cmapIndexes, offset))
}
}
return 0
}
// Name returns the Font's name value for the given NameID. It returns "" if
// there was an error, or if that name was not found.
func (f *Font) Name(id NameID) string {
x, platformID, err := parseSubtables(f.name, "name", 6, 12, func(b []byte) bool {
return NameID(u16(b, 6)) == id
})
if err != nil {
return ""
}
offset, length := u16(f.name, 4)+u16(f.name, x+10), u16(f.name, x+8)
// Return the ASCII value of the encoded string.
// The string is encoded as UTF-16 on non-Apple platformIDs; Apple is platformID 1.
src := f.name[offset : offset+length]
var dst []byte
if platformID != 1 { // UTF-16.
if len(src)&1 != 0 {
return ""
}
dst = make([]byte, len(src)/2)
for i := range dst {
dst[i] = printable(u16(src, 2*i))
}
} else { // ASCII.
dst = make([]byte, len(src))
for i, c := range src {
dst[i] = printable(uint16(c))
}
}
return string(dst)
}
func printable(r uint16) byte {
if 0x20 <= r && r < 0x7f {
return byte(r)
}
return '?'
}
// unscaledHMetric returns the unscaled horizontal metrics for the glyph with
// the given index.
func (f *Font) unscaledHMetric(i Index) (h HMetric) {
j := int(i)
if j < 0 || f.nGlyph <= j {
return HMetric{}
}
if j >= f.nHMetric {
p := 4 * (f.nHMetric - 1)
return HMetric{
AdvanceWidth: fixed.Int26_6(u16(f.hmtx, p)),
LeftSideBearing: fixed.Int26_6(int16(u16(f.hmtx, p+2*(j-f.nHMetric)+4))),
}
}
return HMetric{
AdvanceWidth: fixed.Int26_6(u16(f.hmtx, 4*j)),
LeftSideBearing: fixed.Int26_6(int16(u16(f.hmtx, 4*j+2))),
}
}
// HMetric returns the horizontal metrics for the glyph with the given index.
func (f *Font) HMetric(scale fixed.Int26_6, i Index) HMetric {
h := f.unscaledHMetric(i)
h.AdvanceWidth = f.scale(scale * h.AdvanceWidth)
h.LeftSideBearing = f.scale(scale * h.LeftSideBearing)
return h
}
// unscaledVMetric returns the unscaled vertical metrics for the glyph with
// the given index. yMax is the top of the glyph's bounding box.
func (f *Font) unscaledVMetric(i Index, yMax fixed.Int26_6) (v VMetric) {
j := int(i)
if j < 0 || f.nGlyph <= j {
return VMetric{}
}
if 4*j+4 <= len(f.vmtx) {
return VMetric{
AdvanceHeight: fixed.Int26_6(u16(f.vmtx, 4*j)),
TopSideBearing: fixed.Int26_6(int16(u16(f.vmtx, 4*j+2))),
}
}
// The OS/2 table has grown over time.
// https://developer.apple.com/fonts/TTRefMan/RM06/Chap6OS2.html
// says that it was originally 68 bytes. Optional fields, including
// the ascender and descender, are described at
// http://www.microsoft.com/typography/otspec/os2.htm
if len(f.os2) >= 72 {
sTypoAscender := fixed.Int26_6(int16(u16(f.os2, 68)))
sTypoDescender := fixed.Int26_6(int16(u16(f.os2, 70)))
return VMetric{
AdvanceHeight: sTypoAscender - sTypoDescender,
TopSideBearing: sTypoAscender - yMax,
}
}
return VMetric{
AdvanceHeight: fixed.Int26_6(f.fUnitsPerEm),
TopSideBearing: 0,
}
}
// VMetric returns the vertical metrics for the glyph with the given index.
func (f *Font) VMetric(scale fixed.Int26_6, i Index) VMetric {
// TODO: should 0 be bounds.YMax?
v := f.unscaledVMetric(i, 0)
v.AdvanceHeight = f.scale(scale * v.AdvanceHeight)
v.TopSideBearing = f.scale(scale * v.TopSideBearing)
return v
}
// Kern returns the horizontal adjustment for the given glyph pair. A positive
// kern means to move the glyphs further apart.
func (f *Font) Kern(scale fixed.Int26_6, i0, i1 Index) fixed.Int26_6 {
if f.nKern == 0 {
return 0
}
g := uint32(i0)<<16 | uint32(i1)
lo, hi := 0, f.nKern
for lo < hi {
i := (lo + hi) / 2
ig := u32(f.kern, 18+6*i)
if ig < g {
lo = i + 1
} else if ig > g {
hi = i
} else {
return f.scale(scale * fixed.Int26_6(int16(u16(f.kern, 22+6*i))))
}
}
return 0
}
// Parse returns a new Font for the given TTF or TTC data.
//
// For TrueType Collections, the first font in the collection is parsed.
func Parse(ttf []byte) (font *Font, err error) {
return parse(ttf, 0)
}
func parse(ttf []byte, offset int) (font *Font, err error) {
if len(ttf)-offset < 12 {
err = FormatError("TTF data is too short")
return
}
originalOffset := offset
magic, offset := u32(ttf, offset), offset+4
switch magic {
case 0x00010000:
// No-op.
case 0x74746366: // "ttcf" as a big-endian uint32.
if originalOffset != 0 {
err = FormatError("recursive TTC")
return
}
ttcVersion, offset := u32(ttf, offset), offset+4
if ttcVersion != 0x00010000 && ttcVersion != 0x00020000 {
err = FormatError("bad TTC version")
return
}
numFonts, offset := int(u32(ttf, offset)), offset+4
if numFonts <= 0 {
err = FormatError("bad number of TTC fonts")
return
}
if len(ttf[offset:])/4 < numFonts {
err = FormatError("TTC offset table is too short")
return
}
// TODO: provide an API to select which font in a TrueType collection to return,
// not just the first one. This may require an API to parse a TTC's name tables,
// so users of this package can select the font in a TTC by name.
offset = int(u32(ttf, offset))
if offset <= 0 || offset > len(ttf) {
err = FormatError("bad TTC offset")
return
}
return parse(ttf, offset)
default:
err = FormatError("bad TTF version")
return
}
n, offset := int(u16(ttf, offset)), offset+2
offset += 6 // Skip the searchRange, entrySelector and rangeShift.
if len(ttf) < 16*n+offset {
err = FormatError("TTF data is too short")
return
}
f := new(Font)
// Assign the table slices.
for i := 0; i < n; i++ {
x := 16*i + offset
switch string(ttf[x : x+4]) {
case "cmap":
f.cmap, err = readTable(ttf, ttf[x+8:x+16])
case "cvt ":
f.cvt, err = readTable(ttf, ttf[x+8:x+16])
case "fpgm":
f.fpgm, err = readTable(ttf, ttf[x+8:x+16])
case "glyf":
f.glyf, err = readTable(ttf, ttf[x+8:x+16])
case "hdmx":
f.hdmx, 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])
case "name":
f.name, err = readTable(ttf, ttf[x+8:x+16])
case "OS/2":
f.os2, err = readTable(ttf, ttf[x+8:x+16])
case "prep":
f.prep, err = readTable(ttf, ttf[x+8:x+16])
case "vmtx":
f.vmtx, 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
}
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