refactor(重构提升): 优化转换渲染与资源压缩

ofdgo_pdf_image_cache.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"
+	"crypto/sha256"
+	"image"
+	"image/color"
+	"reflect"
+
+	"github.com/xiaoqidun/pdfgo"
+)
+
+// pdfImageContentKey 区分编码内容、渲染意图、模板填充色及有损采样尺寸
+type pdfImageContentKey struct {
+	data   [32]byte
+	intent pdfgo.Name
+	tint   color.NRGBA64
+	size   image.Point
+}
+
+// pdfImageContent 保存不依赖间接资源的图像描述及已注册编号
+type pdfImageContent struct {
+	source *pdfgo.Image
+	id     string
+}
+
+// pdfImageValueBudget 限制图像描述的检查深度和保留字节数
+type pdfImageValueBudget struct {
+	nodes int
+	bytes int
+}
+
+// imageContentKey 对无间接依赖的小图像生成内容键，超大图像仍沿用流缓存
+// 入参: source 图像描述, key 流缓存键
+// 返回: pdfImageContentKey 内容键, bool 是否可复用, error 取消错误
+func (p *pdfImporter) imageContentKey(source *pdfgo.Image, key pdfImageKey) (pdfImageContentKey, bool, error) {
+	if source == nil || source.Stream == nil || len(source.Stream.Data) > 1<<20 {
+		return pdfImageContentKey{}, false, nil
+	}
+	budget := pdfImageValueBudget{nodes: 256, bytes: 65536}
+	for _, value := range []pdfgo.Object{source.Stream.Dictionary, source.ColorSpace, source.Decode, source.Mask, source.SoftMask} {
+		if !pdfImageDirectValue(value, &budget) {
+			return pdfImageContentKey{}, false, p.ctx.Err()
+		}
+	}
+	hash := sha256.New()
+	data := source.Stream.Data
+	for len(data) != 0 {
+		if err := p.ctx.Err(); err != nil {
+			return pdfImageContentKey{}, false, err
+		}
+		n := min(len(data), 65536)
+		hash.Write(data[:n])
+		data = data[n:]
+	}
+	result := pdfImageContentKey{intent: key.intent, tint: key.tint, size: key.size}
+	hash.Sum(result.data[:0])
+	return result, true, p.ctx.Err()
+}
+
+// pdfImageDirectValue 检查图像描述是否完全独立，拒绝间接引用和嵌套流
+// 入参: value 描述值, budget 描述检查预算
+// 返回: bool 是否不依赖阅读器资源
+func pdfImageDirectValue(value pdfgo.Object, budget *pdfImageValueBudget) bool {
+	if budget.nodes <= 0 || budget.bytes < 64 {
+		return false
+	}
+	budget.nodes--
+	budget.bytes -= 64
+	switch v := value.(type) {
+	case nil, pdfgo.Boolean, pdfgo.Integer, pdfgo.Real:
+		return true
+	case pdfgo.Name:
+		budget.bytes -= len(v)
+		return budget.bytes >= 0
+	case pdfgo.String:
+		budget.bytes -= len(v)
+		return budget.bytes >= 0
+	case pdfgo.Array:
+		for _, child := range v {
+			if !pdfImageDirectValue(child, budget) {
+				return false
+			}
+		}
+		return true
+	case pdfgo.Dictionary:
+		for key, child := range v {
+			budget.bytes -= len(key)
+			if !pdfImageDirectValue(child, budget) {
+				return false
+			}
+		}
+		return true
+	}
+	return false
+}
+
+// matches 核对完整编码与有效图像属性，不以摘要相同代替内容相同
+// 入参: source 待复用图像
+// 返回: bool 是否可使用同一图像资源
+func (c pdfImageContent) matches(source *pdfgo.Image) bool {
+	s := c.source
+	return s.Width == source.Width && s.Height == source.Height && s.BitsPerComponent == source.BitsPerComponent &&
+		s.ImageMask == source.ImageMask && s.Interpolate == source.Interpolate &&
+		bytes.Equal(s.Stream.Data, source.Stream.Data) && reflect.DeepEqual(s.Stream.Dictionary, source.Stream.Dictionary) &&
+		reflect.DeepEqual(s.ColorSpace, source.ColorSpace) && reflect.DeepEqual(s.Decode, source.Decode) &&
+		reflect.DeepEqual(s.Mask, source.Mask) && reflect.DeepEqual(s.SoftMask, source.SoftMask)
+}