feat(文件拆分): 拆分PDF格式适配模块

internal/codec/pdf/page.go

@@ -0,0 +1,40 @@
+// 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 (
+	"github.com/xiaoqidun/pdfgo"
+)
+
+// PageMatrix 将裁剪框、用户单位及页面旋转转换为OFD毫米坐标
+// 入参: page PDF页面
+// 返回: pdfgo.Matrix 坐标变换, float64 页面宽度, float64 页面高度
+func PageMatrix(page *pdfgo.Page) (pdfgo.Matrix, float64, float64) {
+	b := page.CropBox
+	scale := 25.4 / 72 * page.UserUnit
+	width, height := (b.XMax-b.XMin)*scale, (b.YMax-b.YMin)*scale
+	m := pdfgo.Matrix{scale, 0, 0, -scale, -b.XMin * scale, b.YMax * scale}
+	switch page.Rotation {
+	case 90:
+		m = pdfgo.Matrix{0, 1, -1, 0, height, 0}.Mul(m)
+		width, height = height, width
+	case 180:
+		m = pdfgo.Matrix{-1, 0, 0, -1, width, height}.Mul(m)
+	case 270:
+		m = pdfgo.Matrix{0, -1, 1, 0, 0, width}.Mul(m)
+		width, height = height, width
+	}
+	return m, width, height
+}