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font.go
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font.go
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// Package truetype provides support for OpenType and TrueType font formats, used in PDF.
//
// It is largely influenced by github.com/ConradIrwin/font and golang.org/x/image/font/sfnt,
// and FreeType2.
package truetype
import (
"bytes"
"compress/zlib"
"errors"
"fmt"
"io"
"strings"
"github.com/benoitkugler/textlayout/fonts"
type1c "github.com/benoitkugler/textlayout/fonts/type1C"
)
var Loader fonts.FontLoader = loader{}
var _ fonts.Face = (*Font)(nil)
type loader struct{}
type fixed struct {
Major int16
Minor uint16
}
type longdatetime struct {
SecondsSince1904 uint64
}
var (
// errInvalidChecksum is returned by ParseOTF if the font's checksum is wrong
errInvalidChecksum = errors.New("invalid checksum")
// errUnsupportedFormat is returned from Parse if parsing failed
errUnsupportedFormat = errors.New("unsupported font format")
// errMissingTable is returned from *Table if the table does not exist in the font.
errMissingTable = errors.New("missing table")
errUnsupportedTableOffsetLength = errors.New("unsupported table offset or length")
errInvalidDfont = errors.New("invalid dfont")
)
type gid = uint16
// Font represents a SFNT font, which is the underlying representation found
// in .otf and .ttf files.
// SFNT is a container format, which contains a number of tables identified by
// Tags. Depending on the type of glyphs embedded in the file which tables will
// exist. In particular, there's a big different between TrueType glyphs (usually .ttf)
// and CFF/PostScript Type 2 glyphs (usually .otf)
type Font struct {
file fonts.Resource // source, needed to parse each table
tables map[Tag]*tableSection // header only, contents is processed on demand
// Optionnal, only present in variable fonts
avar tableAvar
// cmaps is not empty after successful parsing
cmaps TableCmap
Names TableName
// Advanced layout tables.
layoutTables LayoutTables
metrics
Head TableHead
// NumGlyphs exposes the number of glyph indexes present in the font.
NumGlyphs int
// Type represents the kind of glyphs in this font.
// It is one of TypeTrueType, TypeTrueTypeApple, TypePostScript1, TypeOpenType
Type Tag
// True for fonts which include a 'hbed' table instead
// of a 'head' table. Apple uses it as a flag that a font doesn't have
// any glyph outlines but only embedded bitmaps
isBinary bool
}
// tableSection represents a table within the font file.
type tableSection struct {
offset uint32 // Offset into the file this table starts.
length uint32 // Length of this table within the file.
zLength uint32 // Uncompressed length of this table.
}
// loads the table corresponding to the 'head' tag.
// if a 'bhed' Apple table is present, it replaces the 'head' one
func (font *Font) loadHeadTable() error {
s, hasbhed := font.tables[tagBhed]
if !hasbhed {
var hasHead bool
s, hasHead = font.tables[tagHead]
if !hasHead {
return errors.New("missing required head (or bhed) table")
}
}
font.isBinary = hasbhed
buf, err := font.findTableBuffer(s)
if err != nil {
return err
}
font.Head, err = parseTableHead(buf)
return err
}
// loads the table corresponding to the 'name' tag.
// error only if the table is present and invalid
func (font *Font) tryAndLoadNameTable() error {
s, found := font.tables[tagName]
if !found {
return nil
}
buf, err := font.findTableBuffer(s)
if err != nil {
return err
}
font.Names, err = parseTableName(buf)
return err
}
// GlyfTable parse the 'glyf' table.
// Note that glyphs may be defined in various format (like CFF or bitmaps), and stored
// in other tables.
func (font *Font) GlyfTable() (TableGlyf, error) {
buf, err := font.GetRawTable(tagLoca)
if err != nil {
return nil, err
}
loca, err := parseTableLoca(buf, int(font.NumGlyphs), font.Head.indexToLocFormat == 1)
if err != nil {
return nil, err
}
buf, err = font.GetRawTable(tagGlyf)
if err != nil {
return nil, err
}
return parseTableGlyf(buf, loca)
}
func (font *Font) cffTable() (*type1c.Font, error) {
buf, err := font.GetRawTable(tagCFF)
if err != nil {
return nil, err
}
out, err := type1c.Parse(bytes.NewReader(buf))
if err != nil {
return nil, err
}
if N := out.NumGlyphs(); N != font.NumGlyphs {
return nil, fmt.Errorf("invalid number of glyphs in CFF table (%d != %d)", N, font.NumGlyphs)
}
return out, nil
}
func (font *Font) sbixTable() (tableSbix, error) {
buf, err := font.GetRawTable(tagSbix)
if err != nil {
return tableSbix{}, err
}
return parseTableSbix(buf, int(font.NumGlyphs))
}
// parse cblc and cbdt tables
func (font *Font) colorBitmapTable() (bitmapTable, error) {
buf, err := font.GetRawTable(tagCBLC)
if err != nil {
return nil, err
}
rawImageData, err := font.GetRawTable(tagCBDT)
if err != nil {
return nil, err
}
return parseTableBitmap(buf, rawImageData)
}
// parse eblc and ebdt tables
func (font *Font) grayBitmapTable() (bitmapTable, error) {
buf, err := font.GetRawTable(tagEBLC)
if err != nil {
return nil, err
}
rawImageData, err := font.GetRawTable(tagEBDT)
if err != nil {
return nil, err
}
return parseTableBitmap(buf, rawImageData)
}
// parse bloc and bdat tables
func (font *Font) appleBitmapTable() (bitmapTable, error) {
buf, err := font.GetRawTable(tagBloc)
if err != nil {
return nil, err
}
rawImageData, err := font.GetRawTable(tagBdat)
if err != nil {
return nil, err
}
return parseTableBitmap(buf, rawImageData)
}
func (font *Font) HheaTable() (*TableHVhea, error) {
buf, err := font.GetRawTable(tagHhea)
if err != nil {
return nil, err
}
return parseTableHVhea(buf)
}
func (font *Font) VheaTable() (*TableHVhea, error) {
buf, err := font.GetRawTable(tagVhea)
if err != nil {
return nil, err
}
return parseTableHVhea(buf)
}
func (font *Font) OS2Table() (*TableOS2, error) {
buf, err := font.GetRawTable(tagOS2)
if err != nil {
return nil, err
}
return parseTableOS2(buf)
}
// GPOSTable returns the Glyph Positioning table identified with the 'GPOS' tag.
func (font *Font) GPOSTable() (TableGPOS, error) {
buf, err := font.GetRawTable(TagGpos)
if err != nil {
return TableGPOS{}, err
}
return parseTableGPOS(buf)
}
// GSUBTable returns the Glyph Substitution table identified with the 'GSUB' tag.
func (font *Font) GSUBTable() (TableGSUB, error) {
buf, err := font.GetRawTable(TagGsub)
if err != nil {
return TableGSUB{}, err
}
return parseTableGSUB(buf)
}
// GDEFTable returns the Glyph Definition table identified with the 'GDEF' tag.
func (font *Font) GDEFTable() (TableGDEF, error) {
buf, err := font.GetRawTable(TagGdef)
if err != nil {
return TableGDEF{}, err
}
return parseTableGdef(buf, len(font.fvar.Axis))
}
func (font *Font) loadCmapTable() error {
s, found := font.tables[tagCmap]
if !found {
return errors.New("missing required 'cmap' table")
}
buf, err := font.findTableBuffer(s)
if err != nil {
return fmt.Errorf("invalid required cmap table: %s", err)
}
font.cmaps, err = parseTableCmap(buf)
return err
}
// PostTable returns the Post table names
func (font *Font) PostTable() (PostTable, error) {
buf, err := font.GetRawTable(tagPost)
if err != nil {
return PostTable{}, err
}
return parseTablePost(buf, uint16(font.NumGlyphs))
}
// loadNumGlyphs parses the 'maxp' table to find the number of glyphs in the font.
func (font *Font) loadNumGlyphs() error {
buf, err := font.GetRawTable(tagMaxp)
if err != nil {
return err
}
font.NumGlyphs, err = parseTableMaxp(buf)
return err
}
// HtmxTable returns the glyphs horizontal metrics (array of size numGlyphs),
// expressed in fonts units.
func (font *Font) HtmxTable() (TableHVmtx, error) {
hhea, err := font.HheaTable()
if err != nil {
return nil, err
}
buf, err := font.GetRawTable(tagHmtx)
if err != nil {
return nil, err
}
return parseHVmtxTable(buf, uint16(hhea.numOfLongMetrics), uint16(font.NumGlyphs))
}
// VtmxTable returns the glyphs vertical metrics (array of size numGlyphs),
// expressed in fonts units.
func (font *Font) VtmxTable() (TableHVmtx, error) {
vhea, err := font.VheaTable()
if err != nil {
return nil, err
}
buf, err := font.GetRawTable(tagVmtx)
if err != nil {
return nil, err
}
return parseHVmtxTable(buf, uint16(vhea.numOfLongMetrics), uint16(font.NumGlyphs))
}
// LayoutTables exposes advanced layout tables.
// All the fields are optionnals.
type LayoutTables struct {
GDEF TableGDEF // An absent table has a nil Class
Trak TableTrak
Ankr TableAnkr
Feat TableFeat
Morx TableMorx
Kern TableKernx
Kerx TableKernx
GSUB TableGSUB // An absent table has a nil slice of lookups
GPOS TableGPOS // An absent table has a nil slice of lookups
}
// LayoutTables returns the valid advanced layout tables.
// When parsing yields an error, it is ignored and an empty table is returned.
// See the individual methods for more control over error handling.
func (font *Font) LayoutTables() LayoutTables { return font.layoutTables }
func (font *Font) loadLayoutTables() {
if tb, err := font.GDEFTable(); err == nil {
font.layoutTables.GDEF = tb
}
if tb, err := font.GSUBTable(); err == nil {
font.layoutTables.GSUB = tb
}
if tb, err := font.GPOSTable(); err == nil {
font.layoutTables.GPOS = tb
}
if tb, err := font.MorxTable(); err == nil {
font.layoutTables.Morx = tb
}
if tb, err := font.KernTable(); err == nil {
font.layoutTables.Kern = tb
}
if tb, err := font.KerxTable(); err == nil {
font.layoutTables.Kerx = tb
}
if tb, err := font.AnkrTable(); err == nil {
font.layoutTables.Ankr = tb
}
if tb, err := font.TrakTable(); err == nil {
font.layoutTables.Trak = tb
}
if tb, err := font.FeatTable(); err == nil {
font.layoutTables.Feat = tb
}
}
// KernTable parses and returns the 'kern' table.
func (font *Font) KernTable() (TableKernx, error) {
buf, err := font.GetRawTable(tagKern)
if err != nil {
return nil, err
}
return parseKernTable(buf, int(font.NumGlyphs))
}
// MorxTable parse the AAT 'morx' table.
func (font *Font) MorxTable() (TableMorx, error) {
buf, err := font.GetRawTable(tagMorx)
if err != nil {
return nil, err
}
return parseTableMorx(buf, int(font.NumGlyphs))
}
// KerxTable parse the AAT 'kerx' table.
func (font *Font) KerxTable() (TableKernx, error) {
buf, err := font.GetRawTable(tagKerx)
if err != nil {
return nil, err
}
return parseTableKerx(buf, int(font.NumGlyphs))
}
// AnkrTable parse the AAT 'ankr' table.
func (font *Font) AnkrTable() (TableAnkr, error) {
buf, err := font.GetRawTable(tagAnkr)
if err != nil {
return TableAnkr{}, err
}
return parseTableAnkr(buf, int(font.NumGlyphs))
}
// TrakTable parse the AAT 'trak' table.
func (font *Font) TrakTable() (TableTrak, error) {
buf, err := font.GetRawTable(tagTrak)
if err != nil {
return TableTrak{}, err
}
return parseTrakTable(buf)
}
// FeatTable parse the AAT 'feat' table.
func (font *Font) FeatTable() (TableFeat, error) {
buf, err := font.GetRawTable(tagFeat)
if err != nil {
return nil, err
}
return parseTableFeat(buf)
}
// error only if the table is present and invalid
func (font *Font) tryAndLoadFvarTable() error {
s, found := font.tables[tagFvar]
if !found {
return nil
}
buf, err := font.findTableBuffer(s)
if err != nil {
return err
}
font.fvar, err = parseTableFvar(buf, font.Names)
return err
}
// error only if the table is present and invalid
func (font *Font) tryAndLoadAvarTable() error {
s, found := font.tables[tagAvar]
if !found {
return nil
}
buf, err := font.findTableBuffer(s)
if err != nil {
return err
}
font.avar, err = parseTableAvar(buf, len(font.fvar.Axis))
return err
}
func (font *Font) gvarTable(glyphs TableGlyf) (tableGvar, error) {
buf, err := font.GetRawTable(tagGvar)
if err != nil {
return tableGvar{}, err
}
return parseTableGvar(buf, len(font.fvar.Axis), glyphs)
}
func (font *Font) hvarTable() (tableHVvar, error) {
buf, err := font.GetRawTable(tagHvar)
if err != nil {
return tableHVvar{}, err
}
return parseTableHVvar(buf, len(font.fvar.Axis))
}
func (font *Font) vvarTable() (tableHVvar, error) {
buf, err := font.GetRawTable(tagVvar)
if err != nil {
return tableHVvar{}, err
}
return parseTableHVvar(buf, len(font.fvar.Axis))
}
func (font *Font) mvarTable() (TableMvar, error) {
buf, err := font.GetRawTable(tagMvar)
if err != nil {
return TableMvar{}, err
}
return parseTableMvar(buf, len(font.fvar.Axis))
}
func (font *Font) vorgTable() (tableVorg, error) {
buf, err := font.GetRawTable(tagVorg)
if err != nil {
return tableVorg{}, err
}
return parseTableVorg(buf)
}
// Parse parses an OpenType or TrueType file and returns a Font.
// If `loadAllTables` is false, it only loads the minimal required tables: 'head', 'maxp', 'name' and 'cmap' tables.
// The underlying file is then still needed to access the individual tables, and must not be closed.
// It also always look for an 'fvar' table and parses it if found.
// See Loader for support for collections.
func Parse(file fonts.Resource, loadAllTables bool) (*Font, error) {
return parseOneFont(file, 0, false, loadAllTables)
}
// Load implements fonts.FontLoader. For collection font files (.ttc, .otc),
// multiple fonts may be returned.
// Contrary to `Parse`, all the tables needed for the font metrics are fetched.
func (loader) Load(file fonts.Resource) (fonts.Faces, error) {
_, err := file.Seek(0, io.SeekStart) // file might have been used before
if err != nil {
return nil, err
}
var bytes [4]byte
_, err = file.Read(bytes[:])
if err != nil {
return nil, err
}
magic := newTag(bytes[:])
file.Seek(0, io.SeekStart)
var (
f *Font
offsets []uint32
relativeOffset bool
)
switch magic {
case SignatureWOFF, TypeTrueType, TypeOpenType, TypePostScript1, TypeAppleTrueType:
f, err = parseOneFont(file, 0, false, true)
case ttcTag:
offsets, err = parseTTCHeader(file)
case dfontResourceDataOffset:
offsets, err = parseDfont(file)
relativeOffset = true
default:
return nil, fmt.Errorf("unsupported font format %v", bytes)
}
if err != nil {
return nil, err
}
// only one font
if f != nil {
return fonts.Faces{f}, nil
}
// collection
out := make(fonts.Faces, len(offsets))
for i, o := range offsets {
out[i], err = parseOneFont(file, o, relativeOffset, true)
if err != nil {
return nil, err
}
}
return out, nil
}
// load 'maxp' as well
func parseOneFont(file fonts.Resource, offset uint32, relativeOffset, loadMetrics bool) (f *Font, err error) {
_, err = file.Seek(int64(offset), io.SeekStart)
if err != nil {
return nil, fmt.Errorf("invalid offset: %s", err)
}
var bytes [4]byte
_, err = file.Read(bytes[:])
if err != nil {
return nil, err
}
magic := newTag(bytes[:])
switch magic {
case SignatureWOFF:
f, err = parseWOFF(file, offset, relativeOffset)
case TypeTrueType, TypeOpenType, TypePostScript1, TypeAppleTrueType:
f, err = parseOTF(file, offset, relativeOffset)
default:
// no more collections allowed here
return nil, errUnsupportedFormat
}
if err != nil {
return nil, err
}
err = f.loadNumGlyphs()
if err != nil {
return nil, err
}
err = f.loadCmapTable()
if err != nil {
return nil, err
}
err = f.loadHeadTable()
if err != nil {
return nil, err
}
err = f.tryAndLoadNameTable()
if err != nil {
return nil, err
}
err = f.tryAndLoadFvarTable()
if err != nil {
return nil, err
}
err = f.tryAndLoadAvarTable()
if loadMetrics {
f.loadMetrics()
f.loadLayoutTables()
}
return f, err
}
func (font *Font) findTableBuffer(s *tableSection) ([]byte, error) {
var buf []byte
if s.length != 0 && s.length < s.zLength {
zbuf := io.NewSectionReader(font.file, int64(s.offset), int64(s.length))
r, err := zlib.NewReader(zbuf)
if err != nil {
return nil, err
}
defer r.Close()
buf = make([]byte, s.zLength)
if _, err := io.ReadFull(r, buf); err != nil {
return nil, err
}
} else {
buf = make([]byte, s.length)
if _, err := font.file.ReadAt(buf, int64(s.offset)); err != nil {
return nil, err
}
}
return buf, nil
}
// HasTable returns `true` is the font has the given table.
func (font *Font) HasTable(tag Tag) bool {
_, has := font.tables[tag]
return has
}
// GetRawTable returns the binary content of the given table,
// or an error if not found.
// Note that many tables are already interpreted by this package,
// see the various XXXTable().
func (font *Font) GetRawTable(tag Tag) ([]byte, error) {
s, found := font.tables[tag]
if !found {
return nil, errMissingTable
}
return font.findTableBuffer(s)
}
func (font *Font) PostscriptInfo() (fonts.PSInfo, bool) {
return fonts.PSInfo{}, false
}
func (font *Font) Cmap() (fonts.Cmap, fonts.CmapEncoding) { return font.cmaps.BestEncoding() }
// PoscriptName returns the optional PoscriptName of the font
func (font *Font) PoscriptName() string {
// adapted from freetype
// scan the name table to see whether we have a Postscript name here,
// either in Macintosh or Windows platform encodings
windows, mac := font.Names.getEntry(NamePostscript)
// prefer Windows entries over Apple
if windows != nil {
return windows.String()
}
if mac != nil {
return mac.String()
}
return ""
}
type fontSummary struct {
head *TableHead
os2 *TableOS2
names TableName
hasOutline bool
hasBitmap bool
hasColor bool
hasVerticalInfo bool
}
// loadSummary loads various tables to compute meta data about the font
func (font *Font) loadSummary() (fontSummary, error) {
// adapted from freetype
var out fontSummary
out.names = font.Names
if font.HasTable(tagCBLC) || font.HasTable(tagSbix) || font.HasTable(tagCOLR) {
out.hasColor = true
}
out.head = &font.Head
// do we have outlines in there ?
out.hasOutline = font.HasTable(tagGlyf) || font.HasTable(tagCFF) || font.HasTable(tagCFF2)
isAppleSbix := font.HasTable(tagSbix)
// Apple 'sbix' color bitmaps are rendered scaled and then the 'glyf'
// outline rendered on top. We don't support that yet, so just ignore
// the 'glyf' outline and advertise it as a bitmap-only font.
if isAppleSbix {
out.hasOutline = false
}
isAppleSbit := font.isBinary
hasCblc := font.HasTable(tagCBLC)
hasCbdt := font.HasTable(tagCBDT)
// Ignore outlines for CBLC/CBDT fonts.
if hasCblc || hasCbdt {
out.hasOutline = false
}
out.hasBitmap = hasCblc && hasCbdt || font.HasTable(tagEBDT) && font.HasTable(tagEBLC) || isAppleSbit || isAppleSbix
// OpenType 1.8.2 introduced limits to this value;
// however, they make sense for older SFNT fonts also
if out.head.UnitsPerEm < 16 || out.head.UnitsPerEm > 16384 {
return out, fmt.Errorf("invalid UnitsPerEm value %d", out.head.UnitsPerEm)
}
// do not load the metrics headers and tables if this is an Apple
// sbit font file
if isAppleSbit {
return out, nil
}
// load the `hhea' and `hmtx' tables
_, err := font.HheaTable()
if err == nil {
_, err = font.HtmxTable()
if err != nil {
return out, err
}
} else {
// No `hhea' table necessary for SFNT Mac fonts.
if font.Type == TypeAppleTrueType {
out.hasOutline = false
} else {
return out, errors.New("horizontal header is missing")
}
}
// try to load the `vhea' and `vmtx' tables
if font.HasTable(tagVhea) {
_, err = font.VheaTable()
if err != nil {
return out, err
}
_, err := font.VtmxTable()
out.hasVerticalInfo = err == nil
}
out.os2, _ = font.OS2Table() // we treat the table as missing if there are any errors
return out, nil
}
func (font *Font) LoadSummary() (fonts.FontSummary, error) {
sm, err := font.loadSummary()
if err != nil {
return fonts.FontSummary{}, err
}
isItalic, isBold, familyName, styleName := sm.getStyle()
return fonts.FontSummary{
IsItalic: isItalic,
IsBold: isBold,
Familly: familyName,
Style: styleName,
// a font with no bitmaps and no outlines is scalable;
// it has only empty glyphs then
HasScalableGlyphs: !sm.hasBitmap,
HasBitmapGlyphs: sm.hasBitmap,
HasColorGlyphs: sm.hasColor,
}, nil
}
// getStyle sum up the style of the font
func (summary fontSummary) getStyle() (isItalic, isBold bool, familyName, styleName string) {
// Bit 8 of the `fsSelection' field in the `OS/2' table denotes
// a WWS-only font face. `WWS' stands for `weight', width', and
// `slope', a term used by Microsoft's Windows Presentation
// Foundation (WPF). This flag has been introduced in version
// 1.5 of the OpenType specification (May 2008).
if summary.os2 != nil && summary.os2.FsSelection&256 != 0 {
familyName = summary.names.getName(NamePreferredFamily)
if familyName == "" {
familyName = summary.names.getName(NameFontFamily)
}
styleName = summary.names.getName(NamePreferredSubfamily)
if styleName == "" {
styleName = summary.names.getName(NameFontSubfamily)
}
} else {
familyName = summary.names.getName(NameWWSFamily)
if familyName == "" {
familyName = summary.names.getName(NamePreferredFamily)
}
if familyName == "" {
familyName = summary.names.getName(NameFontFamily)
}
styleName = summary.names.getName(NameWWSSubfamily)
if styleName == "" {
styleName = summary.names.getName(NamePreferredSubfamily)
}
if styleName == "" {
styleName = summary.names.getName(NameFontSubfamily)
}
}
styleName = strings.TrimSpace(styleName)
if styleName == "" { // assume `Regular' style because we don't know better
styleName = "Regular"
}
// Compute style flags.
if summary.hasOutline && summary.os2 != nil {
// We have an OS/2 table; use the `fsSelection' field. Bit 9
// indicates an oblique font face. This flag has been
// introduced in version 1.5 of the OpenType specification.
isItalic = summary.os2.FsSelection&(1<<9) != 0 || summary.os2.FsSelection&1 != 0
isBold = summary.os2.FsSelection&(1<<5) != 0
} else {
// this is an old Mac font, use the header field
isBold = summary.head.MacStyle&1 != 0
isItalic = summary.head.MacStyle&2 != 0
}
return
}