GitHub - novvoo/go-pdf

go-pdf

Go PDF rendering library using Gopdf graphics.

Project Structure

go-pdf/
├── pkg/
│   └── gopdf/          # Core library
│       ├── renderer.go # PDF rendering functionality
│       └── reader.go   # PDF reading functionality
├── cmd/                # Example programs
│   ├── example.go              # Basic usage example
│   ├── circle_comparison.go    # Circle drawing comparison
│   ├── render_demo.go          # Rendering demonstration
│   ├── render_pdf.go           # PDF rendering with layer merging
│   ├── render_pdf_complete.go  # Complete PDF rendering demo
│   └── merge_layers.go         # Layer merging utility
├── go.mod
├── go.sum
├── test.pdf            # Test PDF file
└── README.md

Features

PDF Rendering: Render graphics to PDF using Gopdf
PNG Export: Export rendered content as PNG images
Layer Merging: Merge multiple image layers
Image to PDF: Convert images to PDF format
High DPI Support: Configurable DPI for high-quality output
Image Filters: Support for FlateDecode, DCTDecode, ASCIIHexDecode, RunLengthDecode
Font Loader: Cross-platform font search and management with CJK support
Rendering Comparison: Tools to compare rendering quality with Poppler

Installation

Usage

Basic Example

package main

import (
    "go-pdf/pkg/gopdf"
    
)

func main() {
    // Create renderer
    renderer := gopdf.NewPDFRenderer(600, 400)
    renderer.SetDPI(150)

    // Render to PDF
    renderer.RenderToPDF("output.pdf", func(ctx gopdf.Context) {
        ctx.SetSourceRGB(0.2, 0.4, 0.8)
        ctx.Rectangle(50, 50, 200, 100)
        ctx.Fill()
    })
}

Running Examples

# Basic example
go run cmd/example.go

# Render demo
go run cmd/render_demo.go

# Render PDF with layer merging
go run cmd/render_pdf.go

# Merge layers
go run cmd/merge_layers.go

API Reference

PDFRenderer

NewPDFRenderer(width, height float64) *PDFRenderer

Creates a new PDF renderer with specified dimensions (in points).

SetDPI(dpi float64)

Sets the rendering DPI (default: 72).

RenderToPDF(outputPath string, drawFunc func(ctx gopdf.Context)) error

Renders graphics to a PDF file.

RenderToPNG(outputPath string, drawFunc func(ctx gopdf.Context)) error

Renders graphics to a PNG file.

CreatePDFFromImage(imagePath, outputPath string) error

Creates a PDF from an image file.

PDFReader

NewPDFReader(pdfPath string) *PDFReader

Creates a new PDF reader.

RenderPageToPNG(pageNum int, outputPath string, dpi float64) error

Renders a PDF page to PNG .

RenderPageToImage(pageNum int, dpi float64) (image.Image, error)

Renders a PDF page to an image.Image.

Dependencies

go-pdf - Gopdf graphics bindings for Go
pdfcpu - PDF processing library

Recent Improvements

Image Filters

✅ FlateDecode (zlib decompression)
✅ DCTDecode (JPEG decoding)
✅ ASCIIHexDecode
✅ RunLengthDecode
✅ PNG Predictor support

Font Handling

✅ Cross-platform font search (Windows/macOS/Linux)
✅ Font substitution mechanism
✅ CJK font support
✅ Font fallback chains
✅ Font metrics caching

Testing Tools

✅ Rendering comparison with Poppler
✅ PSNR/MSE quality metrics
✅ Difference image generation
✅ Batch comparison support

Testing

# Run unit tests
cd test
go test -v

# Run rendering comparison (requires Poppler tools)
go run compare_rendering.go ../test.pdf

# Run benchmarks
go test -bench=. -benchmem

License

MIT License