feat(文件归并): 归并PDF适配与解析逻辑

internal/codec/pdf/color.go

@@ -15,6 +15,8 @@
 package pdf
 
 import (
+	"fmt"
+
 	"github.com/xiaoqidun/pdfgo"
 )
 
@@ -35,3 +37,113 @@ func OutputColor(space *pdfgo.ColorSpace, values [4]float64) ([3]float64, error)
 func NormalBlend(mode pdfgo.Name) bool {
 	return mode == "" || mode == "Normal" || mode == "Compatible"
 }
+
+// NativePaint 使用库层色料定义求值设备四色，不以备用色代替原生浓度
+// 入参: paint 源画刷, space 设备四色空间, intent 渲染意图
+// 返回: *pdfgo.Paint 原生画刷或nil, [4]bool 显式通道, error 色料定义错误
+func NativePaint(paint pdfgo.Paint, space *pdfgo.ColorSpace, intent pdfgo.Name) (*pdfgo.Paint, [4]bool, error) {
+	if paint.Colorant == nil {
+		return nil, [4]bool{}, nil
+	}
+	result, err := paint.Colorant.Space.ResolveInGroup(paint.Colorant.Tints, &pdfgo.ColorantDevice{Space: space}, space, intent, false)
+	if err != nil || len(result.Alternates) != 0 {
+		return nil, [4]bool{}, err
+	}
+	return result.Process, result.ProcessMask, nil
+}
+
+// CompositeColor 将原始画刷变换到混合空间，渐变在源空间求值
+// 入参: paint 画刷, point 页面坐标, space 混合空间, intent 渲染意图, conversion 设备转换函数
+// 返回: [4]float64 混合分量, bool 是否着色, error 颜色错误
+func CompositeColor(paint pdfgo.Paint, point pdfgo.Point, space *pdfgo.ColorSpace, intent pdfgo.Name, conversion pdfgo.ColorConversion) ([4]float64, bool, error) {
+	if paint.Shading != nil {
+		return [4]float64{}, false, &pdfgo.UnsupportedError{Feature: "local shading pattern compositing"}
+	}
+	if paint.Tiling != nil {
+		return [4]float64{}, false, &pdfgo.UnsupportedError{Feature: "local tiling pattern compositing"}
+	}
+	var values [4]float64
+	var source *pdfgo.ColorSpace
+	if paint.Function != nil {
+		g := paint.Function
+		if g.Bounds != nil {
+			inverse, ok := g.PatternMatrix.Inverse()
+			if !ok {
+				return values, false, fmt.Errorf("singular function shading bounds transform")
+			}
+			local := inverse.Apply(point)
+			if local.X < g.Bounds.XMin || local.X > g.Bounds.XMax || local.Y < g.Bounds.YMin || local.Y > g.Bounds.YMax {
+				return values, false, nil
+			}
+		}
+		inverse, ok := g.Matrix.Inverse()
+		if !ok {
+			return values, false, fmt.Errorf("singular function shading transform")
+		}
+		local := inverse.Apply(point)
+		source, intent = g.Space, g.Intent
+		if local.X < g.Domain.XMin || local.X > g.Domain.XMax || local.Y < g.Domain.YMin || local.Y > g.Domain.YMax {
+			if g.Background == nil {
+				return values, false, nil
+			}
+			values = *g.Background
+		} else {
+			var err error
+			values, err = g.ValuesAt(local)
+			if err != nil {
+				return values, false, err
+			}
+		}
+	} else if paint.Axial != nil || paint.Radial != nil {
+		var background *[4]float64
+		var bounds *pdfgo.Rectangle
+		var matrix pdfgo.Matrix
+		if g := paint.Axial; g != nil {
+			source, intent = g.Space, g.Intent
+			background, bounds, matrix = g.Background, g.Bounds, g.Matrix
+		} else {
+			g := paint.Radial
+			source, intent = g.Space, g.Intent
+			background, bounds, matrix = g.Background, g.Bounds, g.Matrix
+		}
+		if bounds != nil {
+			local := point
+			if matrix != (pdfgo.Matrix{}) {
+				inverse, ok := matrix.Inverse()
+				if !ok {
+					return values, false, fmt.Errorf("singular shading transform")
+				}
+				local = inverse.Apply(point)
+			}
+			if local.X < bounds.XMin || local.X > bounds.XMax || local.Y < bounds.YMin || local.Y > bounds.YMax {
+				return values, false, nil
+			}
+		}
+		t, visible := ShadingPosition(paint, point)
+		var err error
+		if !visible {
+			if background == nil {
+				return values, false, nil
+			}
+			values = *background
+		} else if paint.Axial != nil {
+			values, err = paint.Axial.ValuesAt(t)
+		} else {
+			values, err = paint.Radial.ValuesAt(t)
+		}
+		if err != nil {
+			return values, false, err
+		}
+	} else if paint.Space != nil {
+		values, source = paint.Values, paint.Space
+	} else if paint.CMYK != nil {
+		values, source = *paint.CMYK, &pdfgo.ColorSpace{Model: "DeviceCMYK"}
+	} else if paint.SourceSpace == "DeviceGray" {
+		values[0], source = paint.RGB[0], &pdfgo.ColorSpace{Model: "DeviceGray"}
+	} else {
+		copy(values[:], paint.RGB[:])
+		source = &pdfgo.ColorSpace{Model: "DeviceRGB"}
+	}
+	values, err := space.ConvertWith(values[:source.Components()], source, intent, conversion)
+	return values, true, err
+}