feat(编辑转换): 增强PDF转换与编辑体验

ofdgo_pdf_mask.go

@@ -0,0 +1,64 @@
+// 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 ofdgo
+
+import (
+	"errors"
+	"fmt"
+	"image"
+	"image/color"
+	"math"
+
+	"github.com/xiaoqidun/pdfgo"
+)
+
+// 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) {
+	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()
+	for y := 0; y < h; y += 256 {
+		for x := 0; x < w; x += 256 {
+			width, height := min(256, w-x), min(256, 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, masks: map[*pdfgo.SoftMask][]float64{}}
+			alpha, err := c.mask(mask, &pdfgo.ColorSpace{Model: "DeviceRGB"})
+			if err != nil {
+				return nil, err
+			}
+			for i, opacity := range alpha {
+				px, py := out.Rect.Min.X+x+i%width, out.Rect.Min.Y+y+i/width
+				pixel := color.NRGBAModel.Convert(source.At(px, py)).(color.NRGBA)
+				pixel.A = uint8(math.Round(float64(pixel.A) * opacity))
+				out.SetNRGBA(px, py, pixel)
+			}
+		}
+	}
+	return out, nil
+}