feat(编辑能力): 新增字体搜索与按需裁剪，完善重叠选择和页块排序

ofdgo_editor_font.go

@@ -0,0 +1,97 @@
+// 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"
+	"fmt"
+	"slices"
+
+	"github.com/tdewolff/font"
+)
+
+// subsetFonts 收集新增字体实际使用的字形，仅裁剪保存结果，不修改编辑资源或原文档字体。
+// 返回: map[string][]byte 包内字体子集, error 错误信息
+func (e *Editor) subsetFonts() (map[string][]byte, error) {
+	used := make(map[string]map[uint16]bool)
+	for _, resource := range e.resources {
+		if resource.font == nil {
+			continue
+		}
+		sfnt := e.fonts[resource.font.ID]
+		if sfnt.IsTrueType && !slices.ContainsFunc([]string{"fvar", "COLR", "CBDT", "sbix", "SVG "}, func(tag string) bool { return sfnt.Tables[tag] != nil }) {
+			used[resource.font.ID] = make(map[uint16]bool)
+		}
+	}
+	for _, page := range e.pages {
+		for _, layer := range page.Content.Layer {
+			for _, object := range layer.Objects {
+				if object.Type != "TextObject" {
+					continue
+				}
+				obj := object.TextObject
+				glyphs := used[obj.Font]
+				if glyphs == nil {
+					continue
+				}
+				for _, code := range obj.TextCode {
+					for _, char := range textCodeRunes(code.Value) {
+						glyphs[e.fonts[obj.Font].GlyphIndex(char)] = true
+					}
+				}
+			}
+		}
+	}
+	result := make(map[string][]byte)
+	for _, resource := range e.resources {
+		if resource.font == nil || len(used[resource.font.ID]) == 0 {
+			continue
+		}
+		glyphs := used[resource.font.ID]
+		glyphs[0] = true
+		ids := make([]uint16, 0, len(glyphs))
+		for id := range glyphs {
+			ids = append(ids, id)
+		}
+		slices.Sort(ids)
+		data, err := subsetEditorFont(resource.data, ids)
+		if err != nil {
+			return nil, fmt.Errorf("subset font %s: %w", resource.font.FontName, err)
+		}
+		if len(data) < len(resource.data) {
+			result[resource.name] = data
+		}
+	}
+	return result, nil
+}
+
+// subsetEditorFont 裁剪TrueType字形及复合依赖，保留字符映射、名称、度量和提示指令。
+// 入参: data 字体数据, glyphs 已排序的字形编号，包含0
+// 返回: []byte 字体子集, error 错误信息
+func subsetEditorFont(data []byte, glyphs []uint16) ([]byte, error) {
+	sfnt, err := font.ParseSFNT(bytes.Clone(data), 0)
+	if err != nil {
+		return nil, err
+	}
+	subset, err := sfnt.Subset(glyphs, font.SubsetOptions{Tables: []string{
+		"cmap", "head", "hhea", "hmtx", "maxp", "OS/2", "post", "glyf", "loca", "cvt ", "fpgm", "prep", "gasp",
+	}})
+	if err != nil {
+		return nil, err
+	}
+	subset.Tables["name"] = sfnt.Tables["name"]
+	clear(subset.Tables["head"][8:12])
+	return serializeOTF(subset.Tables)
+}