feat(文件归并): 归并PDF适配与解析逻辑

ofdgo_pdf_group.go

@@ -22,6 +22,7 @@ import (
 	"math"
 	"reflect"
 
+	baseimage "github.com/xiaoqidun/ofdgo/internal/base/image"
 	codecpdf "github.com/xiaoqidun/ofdgo/internal/codec/pdf"
 	"github.com/xiaoqidun/pdfgo"
 )
@@ -743,3 +744,56 @@ func (p *pdfImporter) maskStyle(style pdfgo.Style) (pdfgo.Style, error) {
 	style.SoftMask = nil
 	return style, nil
 }
+
+// rasterMaskAllowed 仅对不可矢量表达的蒙版启用显式局部合成，格式错误仍返回
+// 入参: err 蒙版转换错误
+// 返回: bool 是否允许局部合成
+func (p *pdfImporter) rasterMaskAllowed(err error) bool {
+	var unsupported *pdfgo.UnsupportedError
+	return p.warning != nil && errors.As(err, &unsupported)
+}
+
+// applySoftMask 按原始颜色分量计算蒙版，逐块应用透明度及亮度传递
+// 入参: source 源图像, box 页面区域, mask PDF软蒙版
+// 返回: image.Image 合成图像, error 蒙版解释或渲染错误
+func (p *pdfImporter) applySoftMask(source image.Image, box Box, mask *pdfgo.SoftMask) (image.Image, error) {
+	if err := p.ctx.Err(); err != nil {
+		return nil, err
+	}
+	inverse, ok := p.matrix.Inverse()
+	if !ok {
+		return nil, fmt.Errorf("invalid PDF mask transform")
+	}
+	out := image.NewNRGBA(source.Bounds())
+	w, h := out.Rect.Dx(), out.Rect.Dy()
+	step := 25.4 / p.rasterDPI
+	cache := p.compositingCache()
+	scratch := &pdfCompositeScratch{}
+	space := &pdfgo.ColorSpace{Model: "DeviceRGB"}
+	for y := 0; y < h; y += pdfCompositeTileSize {
+		for x := 0; x < w; x += pdfCompositeTileSize {
+			if err := p.ctx.Err(); err != nil {
+				return nil, err
+			}
+			width, height := min(pdfCompositeTileSize, w-x), min(pdfCompositeTileSize, h-y)
+			c := pdfCompositor{importer: p, box: Box{X: box.X + float64(x)*step, Y: box.Y + float64(y)*step, W: float64(width) * step, H: float64(height) * step}, width: width, height: height, inverse: inverse, cache: cache, scratch: scratch, masks: map[*pdfgo.SoftMask][]float64{}}
+			alpha, err := c.mask(mask, space)
+			if err != nil {
+				return nil, err
+			}
+			for i, opacity := range alpha {
+				if i%width == 0 {
+					if err := p.ctx.Err(); err != nil {
+						return nil, err
+					}
+				}
+				px, py := out.Rect.Min.X+x+i%width, out.Rect.Min.Y+y+i/width
+				pixel := baseimage.NRGBAAt(source, px, py)
+				pixel.A = uint8(math.Round(float64(pixel.A) * opacity))
+				out.SetNRGBA(px, py, pixel)
+			}
+			c.releaseMasks()
+		}
+	}
+	return out, nil
+}