feat(渲染转换): 完善PDF转换及点线绘制

ofdgo_font_cmap.go

@@ -0,0 +1,122 @@
+// Copyright 2025-2026 肖其顿 (XIAO QI DUN)
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package ofdgo
+
+import (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+)
+
+// normalizeCmap 转换旧式双字节子表，保留各编码记录及原字形编号
+// 入参: data 字符映射表
+// 返回: []byte 等价字符映射表, error 子表错误
+func normalizeCmap(data []byte) ([]byte, error) {
+	if len(data) < 4 {
+		return data, nil
+	}
+	count := int(binary.BigEndian.Uint16(data[2:]))
+	if count > (len(data)-4)/8 {
+		return nil, fmt.Errorf("invalid cmap encoding records")
+	}
+	var out []byte
+	converted := make(map[uint32]uint32)
+	for n := 0; n < count; n++ {
+		record := 8 + 8*n
+		offset := binary.BigEndian.Uint32(data[record:])
+		if uint64(offset)+2 > uint64(len(data)) {
+			return nil, fmt.Errorf("invalid cmap subtable offset")
+		}
+		if binary.BigEndian.Uint16(data[offset:]) != 2 {
+			continue
+		}
+		if out == nil {
+			out = bytes.Clone(data)
+		}
+		next, ok := converted[offset]
+		if !ok {
+			mapping, err := parseCmapFormat2(data[offset:])
+			if err != nil {
+				return nil, err
+			}
+			table := buildCmapTable(0, mapping)
+			subtable := table[binary.BigEndian.Uint32(table[8:]):]
+			language := binary.BigEndian.Uint16(data[offset+4:])
+			if binary.BigEndian.Uint16(subtable) == 12 {
+				binary.BigEndian.PutUint32(subtable[8:], uint32(language))
+			} else {
+				binary.BigEndian.PutUint16(subtable[4:], language)
+			}
+			next = uint32(len(out))
+			converted[offset] = next
+			out = append(out, subtable...)
+		}
+		binary.BigEndian.PutUint32(out[record:], next)
+	}
+	if out == nil {
+		return data, nil
+	}
+	return out, nil
+}
+
+// parseCmapFormat2 解析混合单字节与双字节字符的子头映射
+// 入参: data format 2子表
+// 返回: map[rune]uint16 编码值到字形编号, error 子头或字形数组越界
+func parseCmapFormat2(data []byte) (map[rune]uint16, error) {
+	if len(data) < 526 {
+		return nil, fmt.Errorf("truncated cmap format 2")
+	}
+	length := int(binary.BigEndian.Uint16(data[2:]))
+	if length < 526 || length > len(data) {
+		return nil, fmt.Errorf("invalid cmap format 2 length")
+	}
+	data = data[:length]
+	maxKey := 0
+	for n := 0; n < 256; n++ {
+		key := int(binary.BigEndian.Uint16(data[6+2*n:]))
+		if key%8 != 0 || 518+key+8 > len(data) {
+			return nil, fmt.Errorf("invalid cmap format 2 subheader")
+		}
+		maxKey = max(maxKey, key)
+	}
+	mapping := make(map[rune]uint16)
+	for high := 0; high < 256; high++ {
+		key := 0
+		if high != 0 {
+			key = int(binary.BigEndian.Uint16(data[6+2*high:]))
+			if key == 0 {
+				continue
+			}
+		}
+		pos := 518 + key
+		first, count := int(binary.BigEndian.Uint16(data[pos:])), int(binary.BigEndian.Uint16(data[pos+2:]))
+		delta := binary.BigEndian.Uint16(data[pos+4:])
+		start := pos + 6 + int(binary.BigEndian.Uint16(data[pos+6:]))
+		if first+count > 256 || count > 0 && (start < 526+maxKey || start+count*2 > len(data)) {
+			return nil, fmt.Errorf("invalid cmap format 2 glyph array")
+		}
+		for n := 0; n < count; n++ {
+			low := first + n
+			if high == 0 && binary.BigEndian.Uint16(data[6+2*low:]) != 0 {
+				continue
+			}
+			glyph := binary.BigEndian.Uint16(data[start+2*n:])
+			if glyph != 0 {
+				mapping[rune(high*256+low)] = glyph + delta
+			}
+		}
+	}
+	return mapping, nil
+}