feat(文件拆分): 拆分PDF格式适配模块

internal/codec/pdf/shading.go

@@ -0,0 +1,96 @@
+// 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"
+)
+
+// ShadingColorants 复用原始浓度缓冲及原生通道映射，不跨并发采样共享
+type ShadingColorants struct {
+	paint   pdfgo.Paint
+	Process *pdfgo.ColorantProcess
+	tints   []float64
+	mesh    *pdfgo.MeshSampler
+}
+
+// ShadingColorantSpace 返回渐变的源色料定义，不使用备用颜色推断通道
+// 入参: paint 渐变画刷
+// 返回: *pdfgo.ColorantSpace 原始色料定义，普通渐变为nil
+func ShadingColorantSpace(paint pdfgo.Paint) *pdfgo.ColorantSpace {
+	switch {
+	case paint.Axial != nil:
+		return paint.Axial.ColorantSpace()
+	case paint.Radial != nil:
+		return paint.Radial.ColorantSpace()
+	case paint.Function != nil:
+		return paint.Function.ColorantSpace()
+	case paint.Mesh != nil:
+		return paint.Mesh.ColorantSpace()
+	}
+	return nil
+}
+
+// PrepareShadingColorants 为当前组建立原生过程采样，备用色保留原路径
+// 入参: paint 渐变画刷, space 组空间, softMask 是否用于软蒙版
+// 返回: *ShadingColorants 独立采样状态，不可原生映射时为nil
+func PrepareShadingColorants(paint pdfgo.Paint, space *pdfgo.ColorSpace, softMask bool) *ShadingColorants {
+	colorants := ShadingColorantSpace(paint)
+	Process := colorants.PrepareProcess(&pdfgo.ColorantDevice{Space: space}, space, softMask)
+	if Process == nil || Process.Mask() == ([4]bool{}) {
+		return nil
+	}
+	s := &ShadingColorants{paint: paint, Process: Process, tints: make([]float64, len(colorants.Names))}
+	if paint.Mesh != nil {
+		s.mesh = paint.Mesh.NewSampler()
+	}
+	return s
+}
+
+// At 在归一化位置求值轴向或径向原始浓度
+// 入参: position 归一化渐变参数
+// 返回: [4]float64 原生过程分量, error 求值错误
+func (s *ShadingColorants) At(position float64) ([4]float64, error) {
+	var err error
+	if s.paint.Axial != nil {
+		err = s.paint.Axial.ColorantValuesAt(position, s.tints)
+	} else {
+		err = s.paint.Radial.ColorantValuesAt(position, s.tints)
+	}
+	if err != nil {
+		return [4]float64{}, err
+	}
+	return s.Process.Convert(s.tints)
+}
+
+// PointAt 在函数定义域内求值原始浓度
+// 入参: point 函数坐标
+// 返回: [4]float64 原生过程分量, error 求值错误
+func (s *ShadingColorants) PointAt(point pdfgo.Point) ([4]float64, error) {
+	if err := s.paint.Function.ColorantValuesAt(point, s.tints); err != nil {
+		return [4]float64{}, err
+	}
+	return s.Process.Convert(s.tints)
+}
+
+// MeshAt 插值网格原始浓度并复用函数结果
+// 入参: patch 网格序号, u 横向参数, v 纵向参数
+// 返回: [4]float64 原生过程分量, error 求值错误
+func (s *ShadingColorants) MeshAt(patch int, u, v float64) ([4]float64, error) {
+	if err := s.mesh.ColorantValuesAt(patch, u, v, s.tints); err != nil {
+		return [4]float64{}, err
+	}
+	return s.Process.Convert(s.tints)
+}