add sfnt to woff font converter
This commit is contained in:
Bernard Xie
parent
718daee97c
commit
5f2958ef88
1 changed files with 214 additions and 0 deletions
214
lib/font/font.go
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214
lib/font/font.go
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package font
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import (
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"bytes"
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"compress/zlib"
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"encoding/binary"
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"fmt"
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"math"
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"sort"
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)
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var (
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// sfnt2Woff offset
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SFNT_OFFSET_TAG = 0
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SFNT_OFFSET_CHECKSUM = 4
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SFNT_OFFSET_OFFSET = 8
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SFNT_OFFSET_LENGTH = 12
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// sfnt2Woff entry offset
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SFNT_ENTRY_OFFSET_FLAVOR = 0
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SFNT_ENTRY_OFFSET_VERSION_MAJ = 4
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SFNT_ENTRY_OFFSET_VERSION_MIN = 6
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SFNT_ENTRY_OFFSET_CHECKSUM_ADJUSTMENT = 8
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// woff offset
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WOFF_OFFSET_MAGIC = 0
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WOFF_OFFSET_FLAVOR = 4
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WOFF_OFFSET_SIZE = 8
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WOFF_OFFSET_NUM_TABLES = 12
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WOFF_OFFSET_RESERVED = 14
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WOFF_OFFSET_SFNT_SIZE = 16
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WOFF_OFFSET_VERSION_MAJ = 20
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WOFF_OFFSET_VERSION_MIN = 22
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WOFF_OFFSET_META_OFFSET = 24
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WOFF_OFFSET_META_LENGTH = 28
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WOFF_OFFSET_META_ORIG_LENGTH = 32
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WOFF_OFFSET_PRIV_OFFSET = 36
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WOFF_OFFSET_PRIV_LENGTH = 40
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// woff entry offset
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WOFF_ENTRY_OFFSET_TAG = 0
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WOFF_ENTRY_OFFSET_OFFSET = 4
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WOFF_ENTRY_OFFSET_COMPR_LENGTH = 8
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WOFF_ENTRY_OFFSET_LENGTH = 12
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WOFF_ENTRY_OFFSET_CHECKSUM = 16
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// magic
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MAGIC_WOFF = 0x774f4646
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MAGIC_CHECKSUM_ADJUSTMENT = 0xb1b0afba
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// sizes
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SIZE_OF_WOFF_HEADER = 44
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SIZE_OF_WOFF_ENTRY = 20
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SIZE_OF_SFNT_HEADER = 12
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SIZE_OF_SFNT_TABLE_ENTRY = 16
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)
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type TableEntry struct {
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Tag []byte
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CheckSum uint32
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Offset uint32
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Length uint32
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}
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func longAlign(n uint32) uint32 {
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return (n + 3) & ^uint32(3)
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}
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func calcChecksum(buf []byte) uint32 {
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var sum uint32 = 0
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var nlongs = len(buf) / 4
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for i := 0; i < nlongs; i++ {
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var t = binary.BigEndian.Uint32(buf[i*4:])
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sum = sum + t
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}
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return sum
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}
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// Sfnt2Woff is a native go port of the JS library
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// https://github.com/fontello/ttf2woff
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// that converts sfnt fonts (.ttf and .otf) to .woff fonts
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func Sfnt2Woff(fontBuf []byte) ([]byte, error) {
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numTables := binary.BigEndian.Uint16(fontBuf[4:])
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woffHeader := make([]byte, SIZE_OF_WOFF_HEADER)
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binary.BigEndian.PutUint32(woffHeader[WOFF_OFFSET_MAGIC:], uint32(MAGIC_WOFF))
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binary.BigEndian.PutUint16(woffHeader[WOFF_OFFSET_NUM_TABLES:], numTables)
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binary.BigEndian.PutUint16(woffHeader[WOFF_OFFSET_SFNT_SIZE:], 0)
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binary.BigEndian.PutUint32(woffHeader[WOFF_OFFSET_META_OFFSET:], 0)
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binary.BigEndian.PutUint32(woffHeader[WOFF_OFFSET_META_LENGTH:], 0)
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binary.BigEndian.PutUint32(woffHeader[WOFF_OFFSET_META_ORIG_LENGTH:], 0)
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binary.BigEndian.PutUint32(woffHeader[WOFF_OFFSET_PRIV_OFFSET:], 0)
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binary.BigEndian.PutUint32(woffHeader[WOFF_OFFSET_PRIV_LENGTH:], 0)
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var entries []TableEntry
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for i := 0; i < int(numTables); i++ {
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table := fontBuf[SIZE_OF_SFNT_HEADER+i*SIZE_OF_SFNT_TABLE_ENTRY:]
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entry := TableEntry{
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Tag: table[SFNT_OFFSET_TAG : SFNT_OFFSET_TAG+4],
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CheckSum: binary.BigEndian.Uint32(table[SFNT_OFFSET_CHECKSUM:]),
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Offset: binary.BigEndian.Uint32(table[SFNT_OFFSET_OFFSET:]),
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Length: binary.BigEndian.Uint32(table[SFNT_OFFSET_LENGTH:]),
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}
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entries = append(entries, entry)
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}
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sort.Slice(entries, func(i, j int) bool {
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return string(entries[i].Tag) < string(entries[j].Tag)
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})
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sfntSize := uint32(SIZE_OF_SFNT_HEADER + int(numTables)*SIZE_OF_SFNT_TABLE_ENTRY)
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tableInfo := make([]byte, int(numTables)*SIZE_OF_WOFF_ENTRY)
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for i := 0; i < len(entries); i++ {
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tableEntry := entries[i]
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if string(tableEntry.Tag) != "head" {
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alignTable := fontBuf[tableEntry.Offset : tableEntry.Offset+longAlign(tableEntry.Length)]
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if calcChecksum(alignTable) != tableEntry.CheckSum {
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return nil, fmt.Errorf("checksum error in table: %v", string(tableEntry.Tag))
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}
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}
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binary.BigEndian.PutUint32(tableInfo[i*SIZE_OF_WOFF_ENTRY+WOFF_ENTRY_OFFSET_TAG:], binary.BigEndian.Uint32(tableEntry.Tag))
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binary.BigEndian.PutUint32(tableInfo[i*SIZE_OF_WOFF_ENTRY+WOFF_ENTRY_OFFSET_LENGTH:], tableEntry.Length)
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binary.BigEndian.PutUint32(tableInfo[i*SIZE_OF_WOFF_ENTRY+WOFF_ENTRY_OFFSET_CHECKSUM:], tableEntry.CheckSum)
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sfntSize += longAlign(tableEntry.Length)
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}
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sfntOffset := uint32(SIZE_OF_SFNT_HEADER + len(entries)*SIZE_OF_SFNT_TABLE_ENTRY)
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csum := calcChecksum(fontBuf[:SIZE_OF_SFNT_HEADER])
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for i := 0; i < len(entries); i++ {
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tableEntry := entries[i]
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b := make([]byte, SIZE_OF_SFNT_TABLE_ENTRY)
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binary.BigEndian.PutUint32(b[SFNT_OFFSET_TAG:], binary.BigEndian.Uint32(tableEntry.Tag))
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binary.BigEndian.PutUint32(b[SFNT_OFFSET_CHECKSUM:], tableEntry.CheckSum)
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binary.BigEndian.PutUint32(b[SFNT_OFFSET_OFFSET:], sfntOffset)
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binary.BigEndian.PutUint32(b[SFNT_OFFSET_LENGTH:], tableEntry.Length)
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sfntOffset += longAlign(tableEntry.Length)
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csum += calcChecksum(b)
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csum += tableEntry.CheckSum
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}
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var checksumAdjustment = uint32(MAGIC_CHECKSUM_ADJUSTMENT) - csum
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majorVersion := uint16(0)
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minVersion := uint16(1)
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flavor := uint32(0)
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offset := SIZE_OF_WOFF_HEADER + int(numTables)*SIZE_OF_WOFF_ENTRY
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var tableBytes []byte
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for i := 0; i < len(entries); i++ {
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tableEntry := entries[i]
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sfntData := fontBuf[tableEntry.Offset : tableEntry.Offset+tableEntry.Length]
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if string(tableEntry.Tag) == "head" {
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majorVersion = binary.BigEndian.Uint16(sfntData[SFNT_ENTRY_OFFSET_VERSION_MAJ:])
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minVersion = binary.BigEndian.Uint16(sfntData[SFNT_ENTRY_OFFSET_VERSION_MIN:])
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flavor = binary.BigEndian.Uint32(sfntData[SFNT_ENTRY_OFFSET_FLAVOR:])
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binary.BigEndian.PutUint32(sfntData[SFNT_ENTRY_OFFSET_CHECKSUM_ADJUSTMENT:], uint32(checksumAdjustment))
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}
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var res bytes.Buffer
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w := zlib.NewWriter(&res)
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w.Write(sfntData)
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w.Flush()
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w.Close()
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compLength := math.Min(float64(len(res.Bytes())), float64(len(sfntData)))
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length := longAlign(uint32(compLength))
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table := make([]byte, length)
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// only deflate data if the deflated data is actually smaller
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if len(res.Bytes()) >= len(sfntData) {
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copy(table, sfntData)
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} else {
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copy(table, res.Bytes())
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}
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binary.BigEndian.PutUint32(tableInfo[i*SIZE_OF_WOFF_ENTRY+WOFF_ENTRY_OFFSET_OFFSET:], uint32(offset))
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offset += len(table)
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binary.BigEndian.PutUint32(tableInfo[i*SIZE_OF_WOFF_ENTRY+WOFF_ENTRY_OFFSET_COMPR_LENGTH:], uint32(compLength))
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tableBytes = append(tableBytes, table...)
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}
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woffSize := uint32(len(woffHeader) + len(tableInfo) + len(tableBytes))
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binary.BigEndian.PutUint32(woffHeader[WOFF_OFFSET_SIZE:], woffSize)
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binary.BigEndian.PutUint32(woffHeader[WOFF_OFFSET_SFNT_SIZE:], sfntSize)
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binary.BigEndian.PutUint16(woffHeader[WOFF_OFFSET_VERSION_MAJ:], majorVersion)
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binary.BigEndian.PutUint16(woffHeader[WOFF_OFFSET_VERSION_MIN:], minVersion)
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binary.BigEndian.PutUint32(woffHeader[WOFF_OFFSET_FLAVOR:], flavor)
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var out []byte
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out = append(out, woffHeader...)
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out = append(out, tableInfo...)
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out = append(out, tableBytes...)
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return out, nil
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}
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// gofpdf subset only accepts .ttf fonts
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// func Subset(fontBuf []byte, cutset string) []byte {
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// return gofpdf.UTF8CutFont(fontBuf, cutset)
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// }
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