feat(文件拆分): 拆分PDF格式适配模块

internal/codec/pdf/image.go

@@ -0,0 +1,95 @@
+// 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 (
+	"image"
+	"image/color"
+	"math"
+
+	baseimage "github.com/xiaoqidun/ofdgo/internal/base/image"
+	"github.com/xiaoqidun/pdfgo"
+)
+
+// StencilImage 按当前填充色读取模板图像，不分配整幅彩色样本
+type StencilImage struct {
+	Source image.Image
+	Fill   color.NRGBA64
+}
+
+// NativeImage 按源像素输出原生过程色，不分配完整显示颜色缓冲
+type NativeImage struct {
+	Source *pdfgo.ImageProcess
+	Space  *pdfgo.ColorSpace
+}
+
+// ColorModel 保留填充色和模板的有效采样精度
+// 返回: color.Model 非预乘颜色模型
+func (s *StencilImage) ColorModel() color.Model {
+	model := s.Source.ColorModel()
+	if s.Fill.R%257 == 0 && s.Fill.G%257 == 0 && s.Fill.B%257 == 0 && (model == color.GrayModel || model == color.NRGBAModel || model == color.RGBAModel) {
+		return color.NRGBAModel
+	}
+	return color.NRGBA64Model
+}
+
+// Bounds 返回模板图像的采样边界
+// 返回: image.Rectangle 图像边界
+func (s *StencilImage) Bounds() image.Rectangle { return s.Source.Bounds() }
+
+// At 以模板灰度计算填充覆盖率，不重复变换颜色
+// 入参: x 横向坐标, y 纵向坐标
+// 返回: color.Color 非预乘颜色
+func (s *StencilImage) At(x, y int) color.Color {
+	return s.NRGBA64At(x, y)
+}
+
+// NRGBA64At 直接读取模板覆盖率，保留填充色的有效精度
+// 入参: x 横向坐标, y 纵向坐标
+// 返回: color.NRGBA64 非预乘颜色
+func (s *StencilImage) NRGBA64At(x, y int) color.NRGBA64 {
+	if !image.Pt(x, y).In(s.Bounds()) {
+		return color.NRGBA64{}
+	}
+	gray := baseimage.NRGBA64At(s.Source, x, y)
+	pixel := s.Fill
+	pixel.A = uint16(65535 - gray.R)
+	return pixel
+}
+
+// ColorModel 保留16位原生分量与源透明度
+// 返回: color.Model 非预乘颜色模型
+func (s *NativeImage) ColorModel() color.Model { return color.NRGBA64Model }
+
+// Bounds 返回源图像的完整采样边界
+// 返回: image.Rectangle 原始像素边界
+func (s *NativeImage) Bounds() image.Rectangle { return s.Source.Bounds() }
+
+// At 获取按OFD输出映射的原生颜色
+// 入参: x 横坐标, y 纵坐标
+// 返回: color.Color 非预乘颜色
+func (s *NativeImage) At(x, y int) color.Color { return s.NRGBA64At(x, y) }
+
+// NRGBA64At 按原始精度转换设备过程色，不进行页面采样或备用变换
+// 入参: x 横坐标, y 纵坐标
+// 返回: color.NRGBA64 非预乘颜色
+func (s *NativeImage) NRGBA64At(x, y int) color.NRGBA64 {
+	if !image.Pt(x, y).In(s.Bounds()) {
+		return color.NRGBA64{}
+	}
+	values, alpha := s.Source.ValuesAt(x, y)
+	rgb, _ := OutputColor(s.Space, values)
+	return color.NRGBA64{R: uint16(math.Round(rgb[0] * 65535)), G: uint16(math.Round(rgb[1] * 65535)), B: uint16(math.Round(rgb[2] * 65535)), A: uint16(math.Round(alpha * 65535))}
+}