feat(文件归并): 归并PDF封装并下沉计算逻辑

internal/codec/pdf/text.go

@@ -0,0 +1,102 @@
+// 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 (
+	"math"
+	"reflect"
+
+	"github.com/xiaoqidun/pdfgo"
+)
+
+// MergeReplacement 统一同一替换区段内的坐标原点，不重新塑形或调整字距
+// 入参: marks 连续文字图元, replacement 整段原文
+// 返回: *pdfgo.TextMark 合并文字, bool 是否可等价合并
+func MergeReplacement(marks []*pdfgo.TextMark, replacement *pdfgo.ReplacementText) (*pdfgo.TextMark, bool) {
+	first := marks[0]
+	style := first.Style
+	paint := style.Fill
+	if first.Font == nil || len(first.Font.Program) == 0 || first.Mode != 0 || first.Size <= 0 || first.HorizontalScale <= 0 || first.Clip != nil || style.SoftMask != nil || style.Transfer != nil || style.AlphaIsShape || style.FillOverprint || paint.Alpha != 1 || !NormalBlend(style.BlendMode) || paint.Tiling != nil || paint.Axial != nil || paint.Radial != nil || paint.Mesh != nil || paint.Function != nil {
+		return nil, false
+	}
+	inverse, ok := first.Matrix.Inverse()
+	if !ok {
+		return nil, false
+	}
+	count := 0
+	sequence := first.Sequence
+	for _, mark := range marks {
+		if mark.Font != first.Font || mark.Size != first.Size || mark.HorizontalScale != first.HorizontalScale || mark.Mode != first.Mode || mark.Clip != nil || len(mark.Glyphs) != len(mark.Positions) || !reflect.DeepEqual(mark.Style, style) {
+			return nil, false
+		}
+		if mark.Matrix[0] != first.Matrix[0] || mark.Matrix[1] != first.Matrix[1] || mark.Matrix[2] != first.Matrix[2] || mark.Matrix[3] != first.Matrix[3] {
+			return nil, false
+		}
+		count += len(mark.Glyphs)
+		sequence = CommonSequence(sequence, mark.Sequence)
+	}
+	if count == 0 {
+		return nil, false
+	}
+	merged := *first
+	merged.Replacement = replacement
+	merged.Sequence = sequence
+	merged.Glyphs = make([]pdfgo.Glyph, 0, count)
+	merged.Positions = make([]pdfgo.Point, 0, count)
+	for _, mark := range marks {
+		dx, dy := mark.Matrix[4]-first.Matrix[4], mark.Matrix[5]-first.Matrix[5]
+		offset := pdfgo.Point{X: inverse[0]*dx + inverse[2]*dy, Y: inverse[1]*dx + inverse[3]*dy}
+		for _, point := range mark.Positions {
+			point.X += offset.X
+			point.Y += offset.Y
+			if math.IsNaN(point.X) || math.IsNaN(point.Y) || math.IsInf(point.X, 0) || math.IsInf(point.Y, 0) {
+				return nil, false
+			}
+			merged.Positions = append(merged.Positions, point)
+		}
+		merged.Glyphs = append(merged.Glyphs, mark.Glyphs...)
+	}
+	return &merged, true
+}
+
+// CommonSequence 查找两个内容区段的最近共同外层，不将合并内容归入单个子区段
+// 入参: first 首个区段, second 后续区段
+// 返回: *pdfgo.ContentSequence 共同区段，没有共同区段时为空
+func CommonSequence(first, second *pdfgo.ContentSequence) *pdfgo.ContentSequence {
+	if first == second {
+		return first
+	}
+	if first == nil || second == nil {
+		return nil
+	}
+	depth := func(sequence *pdfgo.ContentSequence) int {
+		count := 0
+		for ; sequence != nil; sequence = sequence.Parent {
+			count++
+		}
+		return count
+	}
+	a, b := depth(first), depth(second)
+	for ; a > b; a-- {
+		first = first.Parent
+	}
+	for ; b > a; b-- {
+		second = second.Parent
+	}
+	for first != second {
+		first, second = first.Parent, second.Parent
+	}
+	return first
+}