feat(文件拆分): 拆分PDF格式适配模块

internal/codec/pdf/rendition.go

@@ -0,0 +1,158 @@
+// 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 pdf
+
+import (
+	"fmt"
+
+	"github.com/xiaoqidun/pdfgo"
+)
+
+// RenditionFloatingWindow 校验浮窗必需的像素尺寸，呈现偏好不写成视频固有尺寸
+// 入参: reader PDF阅读器, screen 媒体屏幕参数
+// 返回: bool 是否具备合法尺寸, error 引用错误
+func RenditionFloatingWindow(reader *pdfgo.Reader, screen pdfgo.Dictionary) (bool, error) {
+	value, err := reader.Resolve(screen["BE"])
+	if err != nil {
+		return false, err
+	}
+	preferences, _ := value.(pdfgo.Dictionary)
+	value, err = reader.Resolve(preferences["F"])
+	if err != nil {
+		return false, err
+	}
+	window, ok := value.(pdfgo.Dictionary)
+	if !ok {
+		return false, nil
+	}
+	value, err = reader.Resolve(window["D"])
+	if err != nil {
+		return false, err
+	}
+	size, ok := value.(pdfgo.Array)
+	if !ok || len(size) != 2 {
+		return false, nil
+	}
+	for _, part := range size {
+		value, err = reader.Resolve(part)
+		if err != nil {
+			return false, err
+		}
+		number, ok := value.(pdfgo.Integer)
+		if !ok || number < 0 {
+			return false, nil
+		}
+	}
+	return true, nil
+}
+
+// RenditionCriteria 检查媒体环境条件，未知尽力处理字段不影响候选可用性
+// 入参: reader PDF阅读器, rendition 媒体呈现或选择器
+// 返回: bool 是否可用, error 条件字典或引用错误
+func RenditionCriteria(reader *pdfgo.Reader, rendition *pdfgo.Rendition) (bool, error) {
+	for _, constraints := range []struct {
+		dict     pdfgo.Dictionary
+		required bool
+	}{{rendition.MustHonor, true}, {rendition.BestEffort, false}} {
+		for key, object := range constraints.dict {
+			if key != "C" {
+				if constraints.required {
+					return false, nil
+				}
+				continue
+			}
+			value, err := reader.Resolve(object)
+			if err != nil {
+				return false, err
+			}
+			criteria, ok := value.(pdfgo.Dictionary)
+			if !ok {
+				return false, fmt.Errorf("invalid media criteria")
+			}
+			for name, object := range criteria {
+				value, err := reader.Resolve(object)
+				if err != nil {
+					return false, err
+				}
+				if name == "Type" && value == pdfgo.Name("MediaCriteria") {
+					continue
+				}
+				switch name {
+				case "Type", "A", "C", "O", "S", "R", "D", "Z", "V", "P", "L":
+					return false, nil
+				default:
+					if constraints.required {
+						return false, nil
+					}
+				}
+			}
+		}
+	}
+	return true, nil
+}
+
+// RenditionParameters 合并可等价表达的播放参数，不支持的偏好不阻断播放
+// 入参: reader PDF阅读器, dict 参数字典, supported 字段及可表达值的检查
+// 返回: pdfgo.Dictionary 合并后的值, bool 是否可用, error 字典或引用错误
+func RenditionParameters(reader *pdfgo.Reader, dict pdfgo.Dictionary, supported map[pdfgo.Name]func(pdfgo.Object) bool) (pdfgo.Dictionary, bool, error) {
+	values := make(pdfgo.Dictionary)
+	for key := range dict {
+		if key != "Type" && key != "MH" && key != "BE" {
+			return nil, false, nil
+		}
+	}
+	value, err := reader.Resolve(dict["MH"])
+	if err != nil {
+		return nil, false, err
+	}
+	mandatory, _ := value.(pdfgo.Dictionary)
+	for _, key := range []pdfgo.Name{"BE", "MH"} {
+		value, err := reader.Resolve(dict[key])
+		if err != nil {
+			return nil, false, err
+		}
+		if value == nil {
+			continue
+		}
+		parameters, ok := value.(pdfgo.Dictionary)
+		if !ok {
+			return nil, false, fmt.Errorf("invalid media playback constraints")
+		}
+		for name, object := range parameters {
+			if _, overridden := mandatory[name]; key == "BE" && overridden {
+				continue
+			}
+			check := supported[name]
+			if check == nil {
+				if key == "MH" {
+					return nil, false, nil
+				}
+				continue
+			}
+			resolved, err := reader.Resolve(object)
+			if err != nil {
+				return nil, false, err
+			}
+			if !check(resolved) {
+				if key == "MH" {
+					return nil, false, nil
+				}
+				continue
+			}
+			values[name] = resolved
+		}
+	}
+	return values, true, nil
+}