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// Copyright 2025-2026 肖其顿 (XIAO QI DUN)
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package ofdgo
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import (
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"bytes"
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"encoding/binary"
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"fmt"
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"maps"
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"math"
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"github.com/go-text/typesetting/font/cff"
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"github.com/go-text/typesetting/font/opentype"
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"github.com/tdewolff/font"
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)
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// defaultCFF2Font 将CFF2默认实例转换为静态OpenType字体，保留字形编号和三次轮廓
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// 入参: data 独立字体数据
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// 返回: []byte 字体数据，非CFF2原样返回, error 解析或编码错误
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func defaultCFF2Font(data []byte) (result []byte, err error) {
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if len(data) < 12 || string(data[:4]) != "OTTO" {
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return data, nil
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}
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found := false
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for i, count := 0, int(binary.BigEndian.Uint16(data[4:])); i < count && i < (len(data)-12)/16; i++ {
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if string(data[12+i*16:16+i*16]) == "CFF2" {
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found = true
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break
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}
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}
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if !found {
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return data, nil
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}
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table, err := fontFileTables(data, 0)
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if err != nil || table["CFF2"] == nil {
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return data, err
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}
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if table["CFF "] != nil || table["glyf"] != nil || len(table["head"]) < 54 || len(table["maxp"]) < 6 || len(table["hhea"]) < 36 {
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return nil, fmt.Errorf("invalid CFF2 font tables")
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}
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defer func() {
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if failure := recover(); failure != nil {
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result, err = nil, fmt.Errorf("invalid CFF2 font: %v", failure)
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}
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}()
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cffData := table["CFF2"]
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if len(cffData) < 5 || cffData[0] != 2 || cffData[1] != 0 || cffData[2] < 5 || binary.BigEndian.Uint32(table["maxp"]) != 0x5000 {
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return nil, fmt.Errorf("invalid CFF2 header")
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}
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start := int(cffData[2])
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end := start + int(binary.BigEndian.Uint16(cffData[3:]))
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if end > len(cffData) {
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return nil, fmt.Errorf("invalid CFF2 dictionary length")
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}
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dict, err := readCFFDictionary(cffData[start:end], true)
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if err != nil {
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return nil, err
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}
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matrix, err := readCFFMatrix(dict, [6]float64{.001, 0, 0, .001, 0, 0})
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units := binary.BigEndian.Uint16(table["head"][18:])
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if err != nil || units < 16 || units > 16384 || matrix[0] != matrix[3] || matrix[1] != 0 || matrix[2] != 0 || matrix[4] != 0 || matrix[5] != 0 || math.Abs(matrix[0]*float64(units)-1) > 1e-6 {
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return nil, fmt.Errorf("CFF2 FontMatrix does not match design units")
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}
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program, err := cff.ParseCFF2(table["CFF2"])
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if err != nil {
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return nil, err
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}
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if len(dict[24]) != 0 {
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fvar := table["fvar"]
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if len(fvar) < 16 || binary.BigEndian.Uint32(fvar) != 0x10000 || int(binary.BigEndian.Uint16(fvar[8:])) != program.VarStore.AxisCount() {
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return nil, fmt.Errorf("CFF2 variation axis count mismatch")
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}
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}
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count := int(binary.BigEndian.Uint16(table["maxp"][4:]))
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metrics := int(binary.BigEndian.Uint16(table["hhea"][34:]))
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if count == 0 || len(program.Charstrings) != count || metrics == 0 || metrics > count || len(table["hmtx"]) < metrics*4+(count-metrics)*2 {
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return nil, fmt.Errorf("invalid CFF2 glyph metrics")
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}
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chars := make([][]byte, count)
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for gid := range chars {
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segments, _, err := program.LoadGlyph(uint16(gid), nil)
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if err != nil {
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return nil, fmt.Errorf("CFF2 glyph %d: %w", gid, err)
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}
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width := binary.BigEndian.Uint16(table["hmtx"][min(gid, metrics-1)*4:])
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chars[gid], err = cffOutlineProgram(segments, width)
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if err != nil {
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return nil, fmt.Errorf("CFF2 glyph %d: %w", gid, err)
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}
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}
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table["CFF "], err = staticCIDFont(table, chars)
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if err != nil {
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return nil, err
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}
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for _, tag := range []string{"CFF2", "fvar", "avar", "STAT", "HVAR", "VVAR", "MVAR", "DSIG"} {
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delete(table, tag)
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}
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return serializeOTF(table)
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}
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// cffOutlineProgram 将默认设计轮廓编码为无子程序的Type2字形
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// 入参: segments 字体设计坐标路径, width 水平字宽
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// 返回: []byte 字形程序, error 坐标超出编码范围
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func cffOutlineProgram(segments []opentype.Segment, width uint16) ([]byte, error) {
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var output bytes.Buffer
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if width < 32768 {
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if err := encodeType2Number(&output, float64(width)); err != nil {
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return nil, err
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}
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} else {
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for range 2 {
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if err := encodeType2Number(&output, float64(width)/2); err != nil {
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return nil, err
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}
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}
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output.Write([]byte{12, 10})
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}
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var x, y float64
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for _, segment := range segments {
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count, op := 1, byte(21)
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switch segment.Op {
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case opentype.SegmentOpMoveTo:
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case opentype.SegmentOpLineTo:
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op = 5
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case opentype.SegmentOpCubeTo:
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count, op = 3, 8
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default:
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return nil, fmt.Errorf("invalid CFF2 path operation")
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}
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for _, point := range segment.Args[:count] {
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nx, ny := float64(point.X), float64(point.Y)
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if err := encodeType2Number(&output, nx-x); err != nil {
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return nil, err
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}
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if err := encodeType2Number(&output, ny-y); err != nil {
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return nil, err
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}
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x, y = nx, ny
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}
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output.WriteByte(op)
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}
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output.WriteByte(14)
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return output.Bytes(), nil
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}
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// staticCIDFont 封装独立Type2字形，CID与字形编号一致，不依赖字形名称
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// 入参: table OpenType表, chars 字形程序
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// 返回: []byte CFF字体, error 字体结构错误
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func staticCIDFont(table map[string][]byte, chars [][]byte) ([]byte, error) {
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if len(chars) == 0 || len(chars) > 65535 || len(table["head"]) < 54 {
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return nil, fmt.Errorf("invalid static CFF glyph count")
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}
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units := binary.BigEndian.Uint16(table["head"][18:])
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if units < 16 || units > 16384 {
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return nil, fmt.Errorf("invalid CFF design units")
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}
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name := fontFaceInfo(table["name"], 0).PostScriptName
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if name == "" {
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name = "OpenTypeInstance"
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}
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names := encodeCFFIndex([][]byte{[]byte(name)})
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strings := encodeCFFIndex([][]byte{[]byte("Adobe"), []byte("Identity")})
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charset := []byte{0}
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for gid := 1; gid < len(chars); gid++ {
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charset = binary.BigEndian.AppendUint16(charset, uint16(gid))
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}
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selects := []byte{3, 0, 1, 0, 0, 0}
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selects = binary.BigEndian.AppendUint16(selects, uint16(len(chars)))
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fonts := encodeCFFIndex([][]byte{encodeCFFDict(cffDict{18: {0, 0}})})
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charIndex := encodeCFFIndex(chars)
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scale := 1 / float64(units)
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dict := cffDict{1230: {391, 392, 0}, 1234: {float64(len(chars))}, 1207: {scale, 0, 0, scale, 0, 0}, 15: {0}, 17: {0}, 1236: {0}, 1237: {0}}
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for i := 0; i < 4; i++ {
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dict[5] = append(dict[5], float64(int16(binary.BigEndian.Uint16(table["head"][36+2*i:]))))
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}
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var top []byte
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for range 16 {
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top = encodeCFFIndex([][]byte{encodeCFFDict(dict)})
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offset := 4 + len(names) + len(top) + len(strings) + 2
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if dict[15][0] == float64(offset) {
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var output bytes.Buffer
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for _, part := range [][]byte{{1, 0, 4, 4}, names, top, strings, {0, 0}, charset, selects, fonts, charIndex} {
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output.Write(part)
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}
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return output.Bytes(), nil
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}
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dict[15][0] = float64(offset)
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dict[1237][0] = float64(offset + len(charset))
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dict[1236][0] = float64(offset + len(charset) + len(selects))
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dict[17][0] = float64(offset + len(charset) + len(selects) + len(fonts))
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}
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return nil, fmt.Errorf("CFF offsets did not converge")
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}
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// staticCFFPrograms 读取无子程序和私有字典的CID字形，其他CFF保留原有保存策略
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// 入参: sfnt 已解析字体
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// 返回: [][]byte 独立字形程序，不符合条件时为空
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func staticCFFPrograms(sfnt *font.SFNT) [][]byte {
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data := sfnt.Tables["CFF "]
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if len(data) < 4 {
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return nil
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}
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_, end, err := readType2Index(data, int(data[2]))
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if err != nil {
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return nil
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}
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tops, end, err := readType2Index(data, end)
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if err != nil || len(tops) != 1 {
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return nil
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}
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_, end, err = readType2Index(data, end)
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if err != nil {
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return nil
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}
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globals, _, err := readType2Index(data, end)
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if err != nil || len(globals) != 0 {
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return nil
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}
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dict, err := readCFFDict(tops[0])
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if err != nil || len(dict[1230]) != 3 {
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return nil
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}
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matrix, err := readCFFMatrix(dict, [6]float64{.001, 0, 0, .001, 0, 0})
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if err != nil || matrix[0] != matrix[3] || matrix[1] != 0 || matrix[2] != 0 || matrix[4] != 0 || matrix[5] != 0 || math.Abs(matrix[0]*float64(sfnt.UnitsPerEm())-1) > 1e-6 {
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return nil
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}
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offset, err := cffDictOffset(data, dict, 1236)
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if err != nil {
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return nil
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}
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fds, _, err := readType2Index(data, offset)
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if err != nil || len(fds) != 1 {
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return nil
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}
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fd, err := readCFFDict(fds[0])
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if err != nil || len(fd) != 1 || len(fd[18]) != 2 || fd[18][0] != 0 {
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return nil
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}
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offset, err = cffDictOffset(data, dict, 17)
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if err != nil {
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return nil
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}
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chars, _, err := readType2Index(data, offset)
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if err != nil || len(chars) != int(sfnt.NumGlyphs()) {
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return nil
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}
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return chars
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}
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// subsetStaticCFFFont 裁剪静态CID字形并保留原编号、字符映射和度量
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// 入参: sfnt 已解析字体, glyphs 使用的字形
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// 返回: []byte 字体子集, error 裁剪错误
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func subsetStaticCFFFont(sfnt *font.SFNT, glyphs []uint16) ([]byte, error) {
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chars := staticCFFPrograms(sfnt)
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if chars == nil {
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return nil, fmt.Errorf("CFF font cannot be subset safely")
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}
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keep := make(map[uint16]bool, len(glyphs)+1)
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keep[0] = true
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for _, gid := range glyphs {
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if int(gid) >= len(chars) {
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return nil, fmt.Errorf("CFF glyph index out of range")
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}
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keep[gid] = true
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}
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empty := make(map[uint16][]byte)
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for gid := range chars {
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if !keep[uint16(gid)] {
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width := sfnt.GlyphAdvance(uint16(gid))
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program := empty[width]
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if program == nil {
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var err error
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program, err = cffOutlineProgram(nil, width)
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if err != nil {
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return nil, err
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}
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empty[width] = program
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}
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chars[gid] = program
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}
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}
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table := maps.Clone(sfnt.Tables)
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var err error
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table["CFF "], err = staticCIDFont(table, chars)
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if err != nil {
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return nil, err
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}
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mapping := make(map[rune]uint16)
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for gid := range keep {
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for _, char := range sfnt.Cmap.ToUnicode(gid) {
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mapping[char] = gid
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}
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}
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table["cmap"] = buildCmapTable(sfnt.NumGlyphs(), mapping)
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for _, tag := range []string{"DSIG", "GSUB", "GPOS", "GDEF"} {
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delete(table, tag)
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}
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return serializeOTF(table)
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}
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