feat(文档压缩): 支持输出压缩并优化布局

ofdgo_renderer_eps_compression.go

@@ -0,0 +1,104 @@
+// 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 (
+	"bytes"
+	"compress/zlib"
+	"context"
+	"encoding/ascii85"
+	"fmt"
+	"image"
+	"image/jpeg"
+	"io"
+
+	"github.com/tdewolff/canvas"
+	"github.com/tdewolff/canvas/renderers/ps"
+	"github.com/xiaoqidun/pdfgo"
+)
+
+// epsImageRenderer 在EPS输出端优化图片，不修改页面及渲染缓存
+type epsImageRenderer struct {
+	*ps.PS
+	writer  io.Writer
+	options CompressionOptions
+	ctx     context.Context
+	err     error
+}
+
+// RenderImage 写出Flate或更小的JPEG图片，保留原尺寸与变换
+// 入参: img 图片, matrix 绘制变换
+func (r *epsImageRenderer) RenderImage(img image.Image, matrix canvas.Matrix) {
+	if r.err != nil {
+		return
+	}
+	bounds := img.Bounds()
+	width, height := bounds.Dx(), bounds.Dy()
+	pixels := make([]byte, width*3)
+	var encoded bytes.Buffer
+	compressor, _ := zlib.NewWriterLevel(&encoded, zlib.BestCompression)
+	opaque := true
+	for y := 0; y < height; y++ {
+		if r.err = r.ctx.Err(); r.err != nil {
+			return
+		}
+		clear(pixels)
+		for x := 0; x < width; x++ {
+			red, green, blue, alpha := img.At(bounds.Min.X+x, bounds.Min.Y+y).RGBA()
+			if alpha != 65535 {
+				opaque = false
+			}
+			if alpha != 0 {
+				offset := x * 3
+				pixels[offset], pixels[offset+1], pixels[offset+2] = byte(red*65535/alpha>>8), byte(green*65535/alpha>>8), byte(blue*65535/alpha>>8)
+			}
+		}
+		if _, r.err = compressor.Write(pixels); r.err != nil {
+			return
+		}
+	}
+	if r.err = compressor.Close(); r.err != nil {
+		return
+	}
+	data := encoded.Bytes()
+	filter := "FlateDecode"
+	if opaque && r.options.Mode == CompressionLossy {
+		var candidate bytes.Buffer
+		if r.err = jpeg.Encode(&candidate, img, &jpeg.Options{Quality: r.options.ImageQuality()}); r.err != nil {
+			return
+		}
+		optimized, err := pdfgo.OptimizeJPEG(r.ctx, candidate.Bytes())
+		if err != nil {
+			r.err = err
+			return
+		}
+		if len(optimized) < len(data) {
+			data, filter = optimized, "DCTDecode"
+		}
+	}
+	m := matrix.Scale(float64(width), float64(height))
+	_, r.err = fmt.Fprintf(r.writer, " gsave /DeviceRGB setcolorspace [%s %s %s %s %s %s] concat <</ImageType 1 /BitsPerComponent 8 /Decode [0 1 0 1 0 1] /Interpolate true /Width %d /Height %d /ImageMatrix [%d 0 0 -%d 0 %d] /DataSource currentfile /ASCII85Decode filter /%s filter>>image\n", ofdNumber(m[0][0]), ofdNumber(m[1][0]), ofdNumber(m[0][1]), ofdNumber(m[1][1]), ofdNumber(m[0][2]), ofdNumber(m[1][2]), width, height, width, height, height, filter)
+	if r.err != nil {
+		return
+	}
+	writer := ascii85.NewEncoder(r.writer)
+	if _, r.err = writer.Write(data); r.err != nil {
+		return
+	}
+	if r.err = writer.Close(); r.err != nil {
+		return
+	}
+	_, r.err = io.WriteString(r.writer, "~>\n grestore")
+}