Lxman.PdfLibrary.Rendering.SkiaSharp 0.5.0-beta

PdfLibrary

A comprehensive .NET library for parsing, rendering, and creating PDF documents. Built with C# and targeting .NET 10.

Features

PDF Rendering

• Full PDF 1.x and 2.0 parsing support
• High-quality rendering using SkiaSharp
• Support for complex graphics operations (paths, clipping, transparency)
• Comprehensive color space support (DeviceRGB, DeviceCMYK, DeviceGray, ICCBased, Separation, Lab)
• Image handling with custom high-performance decompressors:
  • JPEG (in-house JpegCodec — baseline and progressive)
  • JPEG2000 (JP2/J2K via in-house Jp2Codec)
  • CCITT Group 3 and Group 4 fax compression
  • JBIG2 monochrome compression
  • LZW compression
  • FlateDecode (zlib/PNG)
  • RunLength, ASCII85, ASCIIHex encoding
• Font rendering (Type1, TrueType, CID, embedded fonts)
• Text extraction and positioning

PDF Creation (Fluent Builder API)

• Intuitive fluent API for document creation
• Text with full styling (fonts, colors, spacing)
• Vector graphics (rectangles, circles, lines, paths)
• Image embedding (JPEG, PNG)
• Interactive forms (text fields, checkboxes, radio buttons, dropdowns)
• Annotations (links, notes, highlights)
• Bookmarks/Outlines with hierarchical navigation
• Page labels (custom numbering schemes)
• Layers (Optional Content Groups)
• Encryption (RC4, AES-128, AES-256)
• Custom font embedding (TrueType, OpenType)

Project Structure

PDF/
├── PdfLibrary/                       # Core library
│   ├── Document/                     # PDF document model
│   ├── Structure/                    # PDF structure (xref, trailer, objects)
│   ├── Parsing/                      # PDF lexer/parser
│   ├── Content/                      # Content stream processing
│   ├── Filters/                      # Stream decode filters (Flate, JBIG2Decode, etc.)
│   ├── Rendering/                    # Rendering pipeline
│   ├── Builder/                      # Fluent API for PDF creation
│   ├── Fonts/                        # Font handling
│   ├── Functions/                    # PDF function objects
│   ├── Fixups/                       # Per-document corrective passes
│   ├── Core/                         # Primitive types
│   └── Security/                     # Encryption/decryption
├── PdfLibrary.Rendering.SkiaSharp/   # SkiaSharp render target
├── PdfLibrary.Tests/                 # Unit tests
├── PdfLibrary.Integration/           # Integration tests
├── PdfLibrary.Wpf.Viewer/            # WPF PDF viewer application
├── PdfLibrary.Utilities/             # Utility applications
│   └── ImageUtility/                 # Image format viewer with codec system
├── PdfLibrary.Examples/              # Standalone usage samples
├── ImageLibrary/                     # Pure-C# image format library — one project per codec
│   ├── CcittCodec/                   # CCITT Group 3 (1D/2D) and Group 4 fax
│   ├── LzwCodec/                     # LZW compression (with Early Change support)
│   ├── JpegCodec/                    # JPEG (baseline + progressive, encode + decode)
│   ├── Jbig2Decoder/                 # JBIG2 decoder (ITU-T T.88)
│   ├── BmpCodec/                     # BMP container
│   ├── GifCodec/                     # GIF container (with LZW)
│   ├── PngCodec/                     # PNG container
│   ├── TgaCodec/                     # TGA container
│   ├── TiffCodec/                    # TIFF container (uses CcittCodec + LzwCodec)
│   ├── CcittCodec.Tests/
│   ├── LzwCodec.Tests/
│   ├── JpegCodec.Tests/
│   ├── Jbig2Decoder.Tests/
│   ├── BmpCodec.Tests/
│   ├── GifCodec.Tests/
│   ├── PngCodec.Tests/
│   ├── TgaCodec.Tests/
│   └── ImageLibrary.IntegrationTests/
├── FontParser/                       # TrueType/OpenType parsing
├── Logging/                          # Logging infrastructure
└── Docs/                             # Documentation

Quick Start

Rendering a PDF

using PdfLibrary.Structure;
using PdfLibrary.Rendering.SkiaSharp;

// Load a PDF document
using var stream = File.OpenRead("document.pdf");
var document = PdfDocument.Load(stream);

// Get the page to render
var page = document.GetPage(0);  // 0-based index

// Render to file using the fluent API
page.Render(document)
    .WithScale(1.0)  // 1.0 = 72 DPI
    .ToFile("output.png");

// Or render to SKImage for further processing
using var image = page.Render(document)
    .WithDpi(144)  // 2x resolution
    .ToImage();

Creating a PDF

using PdfLibrary.Builder;

PdfDocumentBuilder.Create()
    .WithMetadata(meta => meta
        .Title("My Document")
        .Author("John Doe"))
    .AddPage(page => page
        .AddText("Hello, World!", 100, 700)
            .WithFont("Helvetica-Bold")
            .WithSize(24)
            .WithColor(PdfColor.Blue)
        .AddRectangle(100, 650, 200, 30)
            .Fill(PdfColor.LightGray)
            .Stroke(PdfColor.Black))
    .AddPage(page => page
        .AddText("Page 2", 100, 700))
    .AddBookmark("Page 1", 0)
    .AddBookmark("Page 2", 1)
    .Save("output.pdf");

Creating a Form

PdfDocumentBuilder.Create()
    .AddPage(page => page
        .AddText("Registration Form", 100, 750)
            .WithSize(18)
            .Bold()
        .AddText("Name:", 100, 700)
        .AddTextField("name", 170, 695, 200, 25)
            .Required()
        .AddText("Email:", 100, 660)
        .AddTextField("email", 170, 655, 200, 25)
        .AddText("I agree to terms:", 100, 620)
        .AddCheckbox("agree", 220, 618, 18, 18))
    .WithAcroForm(form => form.SetNeedAppearances(true))
    .Save("form.pdf");

Advanced Rendering Options

// Render with custom background color
using var image = page.Render(document)
    .WithDpi(300)  // High resolution for printing
    .WithBackgroundColor(new SKColor(255, 250, 240))  // Antique white
    .ToImage();

// Render specific region of page
using var cropImage = page.Render(document)
    .WithScale(2.0)
    .WithCropBox(100, 100, 400, 600)  // x, y, width, height
    .ToImage();

Text Extraction

// Extract all text from a page
var page = document.GetPage(0);
var textContent = page.ExtractText(document);

// Extract text with positioning information
var textBlocks = page.ExtractTextBlocks(document);
foreach (var block in textBlocks)
{
    Console.WriteLine($"Text: {block.Text}");
    Console.WriteLine($"Position: ({block.X}, {block.Y})");
    Console.WriteLine($"Font: {block.FontName}, Size: {block.FontSize}");
}

Thread Safety

PdfLibrary is not currently thread-safe. The two main constraints:

• PdfDocument instances are not safe to share across threads — they lazy-load objects by mutating internal state and seeking a shared Stream.
• The renderer's static glyph cache is cleared whenever SkiaSharpRenderTarget sees a different document, which can race when multiple renders run concurrently and cause silent rendering glitches under load.

For ASP.NET Core or any multi-threaded server use, the safe pattern today is:

1. Load and dispose a fresh PdfDocument per request — never cache or share instances across requests.
2. Serialize render calls with a process-wide SemaphoreSlim(1, 1).

private static readonly SemaphoreSlim RenderLock = new(1, 1);

public async Task<byte[]> RenderFirstPageAsync(string pdfPath)
{
    await RenderLock.WaitAsync();
    try
    {
        using var document = PdfDocument.Load(pdfPath);
        return document.GetPage(0)!
            .RenderTo()
            .WithDpi(150)
            .ToBytes();
    }
    finally
    {
        RenderLock.Release();
    }
}

Proper concurrent rendering is on the roadmap. Until then the throughput ceiling is one render at a time per process — fine for occasional PDF generation, not ideal for high-traffic endpoints. If the same PDFs are requested repeatedly, cache the rendered output at the HTTP layer rather than re-rendering.

Image Decompression Architecture

PdfLibrary uses custom-built, high-performance decompression libraries for all PDF image formats. These are pure C# implementations with no external dependencies:

Custom Decompressors

• JpegCodec - DCTDecode filter (in-house, baseline + progressive JPEG, encode + decode)
• Jp2Codec - JPXDecode filter, in-house JPEG 2000 decoder (decode only)
• CcittCodec - CCITTFaxDecode filter (Group 3 1D/2D and Group 4)
• Jbig2Decoder - JBIG2Decode filter for monochrome document compression (ITU-T T.88, used directly by PdfLibrary.Filters.Jbig2DecodeFilter)
• LzwCodec - LZWDecode filter with Early Change support
• PdfLibrary.Filters.FlateDecodeFilter - FlateDecode (DEFLATE) using System.IO.Compression

Integration

PDF stream filters in PdfLibrary/Filters/ are thin adapters: each maps PDF filter parameters onto the underlying codec library and returns decoded bytes in the layout the renderer expects. Image containers (BMP/GIF/PNG/TGA/TIFF/PBM) live in their own per-codec projects under ImageLibrary/ and are used by the standalone ImageUtility application; PDF rendering only consumes the codec layer (JpegCodec, Jp2Codec, LzwCodec, CcittCodec, Jbig2Decoder).

Requirements

• .NET 10.0 or later
• SkiaSharp (for rendering - separate PdfLibrary.Rendering.SkiaSharp package)

Core Dependencies

• Serilog - Structured logging
• Unicolour - Advanced color space transformations
• In-tree codec libraries (all pure C#, no third-party codec dependencies):
  • ImageLibrary/JpegCodec - JPEG (DCTDecode) baseline and progressive
  • ImageLibrary/Jp2Codec - JPEG 2000 (JPXDecode), decode only
  • ImageLibrary/LzwCodec - LZW (LZWDecode) with Early Change support
  • ImageLibrary/CcittCodec - CCITT (CCITTFaxDecode) Group 3 1D/2D and Group 4
  • ImageLibrary/Jbig2Decoder - JBIG2 (JBIG2Decode, ITU-T T.88)

Note: PdfLibrary has no third-party image-format dependencies. All image handling is backed by in-tree codecs.

Building

# Clone the repository
git clone https://github.com/lxman/PDF.git
cd PDF

# Build the solution
dotnet build PdfLibrary.slnx

# Run tests
dotnet test PdfLibrary.Tests/PdfLibrary.Tests.csproj

All codec implementations are in-tree (no git submodules required).

Documentation

• Fluent API Reference - Complete guide to the PDF creation API
• Getting Started - Step-by-step introduction
• Architecture - Technical architecture overview

Supported PDF Features

Content Streams

• Graphics state operators (q, Q, cm, w, J, j, M, d, ri, i, gs)
• Path operators (m, l, c, v, y, h, re, S, s, f, F, f*, B, B*, b, b*, n, W, W*)
• Text operators (BT, ET, Tc, Tw, Tz, TL, Tf, Tr, Ts, Td, TD, Tm, T*, Tj, TJ, ', ")
• Color operators (CS, cs, SC, SCN, sc, scn, G, g, RG, rg, K, k)
• XObject operators (Do)
• Inline image operators (BI, ID, EI)
• Marked content operators (MP, DP, BMC, BDC, EMC)

Color Spaces

• DeviceGray, DeviceRGB, DeviceCMYK
• CalGray, CalRGB, Lab
• ICCBased
• Indexed
• Separation, DeviceN
• Pattern (tiling and shading)

Fonts

• Type1, Type1C (CFF)
• TrueType
• Type0 (CID fonts)
• Type3
• Embedded and system fonts

Images

• DCTDecode (JPEG)
• FlateDecode (PNG/zlib)
• LZWDecode
• CCITTFaxDecode (Group 3 and 4)
• JBIG2Decode
• JPXDecode (JPEG2000)
• RunLengthDecode
• ASCII85Decode, ASCIIHexDecode

Security

• RC4 40-bit and 128-bit encryption
• AES 128-bit and 256-bit encryption
• Permission flags

License

This project is licensed under the MIT License - see the LICENSE file for details.

Contributing

Contributions are welcome! Please feel free to submit a Pull Request. For major changes, please open an issue first to discuss what you would like to change.

Development Setup

1. Fork the repository
2. Create your feature branch (git checkout -b feature/AmazingFeature)
3. Commit your changes (git commit -m 'Add some AmazingFeature')
4. Push to the branch (git push origin feature/AmazingFeature)
5. Open a Pull Request

Code Style

• Follow C# coding conventions
• Use meaningful variable and method names
• Add XML documentation for public APIs
• Include unit tests for new features

Acknowledgments

Core Library

• SkiaSharp - 2D graphics library for PDF rendering
• Serilog - Structured logging framework
• Unicolour - Advanced color space handling and transformations

Test-time references

• Melville.CSJ2K - Used only by ImageLibrary/Jp2Codec.Tests as a differential reference for in-house JPEG 2000 conformance testing; not a runtime dependency of PdfLibrary.