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DirectWrite Rasterizer

DirectWrite rasterizer backend using TerraFX.Interop.Windows bindings. Provides access to Windows' modern text rendering APIs including color font and variable font support.

Installation

dotnet add package KernSmith.Rasterizers.DirectWrite.TerraFX

Platform: Windows only (net10.0-windows)

Usage

The rasterizer auto-registers via [ModuleInitializer] -- referencing the package is sufficient. Select it in options:

var options = new FontGeneratorOptions
{
    Size = 32,
    RasterizerBackend = RasterizerBackend.DirectWrite
};

var result = BmFont.Generate("path/to/font.ttf", options);

For color fonts with a specific palette:

var options = new FontGeneratorOptions
{
    Size = 32,
    RasterizerBackend = RasterizerBackend.DirectWrite,
    ColorPaletteIndex = 0
};

For variable fonts with custom axis values:

var options = new FontGeneratorOptions
{
    Size = 32,
    RasterizerBackend = RasterizerBackend.DirectWrite,
    VariationAxes = new Dictionary<string, float> { ["wght"] = 700, ["wdth"] = 100 }
};

Capabilities

  • Color font support (COLR/CPAL)
  • Variable font axes (fvar)
  • High-quality ClearType-style subpixel rendering
  • System font loading by family name
  • Synthetic bold and italic
  • TTF, OTF, WOFF, WOFF2 input
  • Fractional font sizes (e.g. Size = 32.5f) honored natively

Limitations

  • Windows only -- will not load on Linux or macOS
  • Requires net10.0-windows (not net8.0-windows)
  • No SDF rendering support -- use FreeType for SDF
  • No outline stroke support

Implementation

Uses an isolated IDWriteFactory5 instance and loads fonts into memory via IDWriteInMemoryFontFileLoader. All COM interop is handled internally.

When to Use

Use DirectWrite when you need color font or variable font support on Windows, or want DirectWrite's high-quality rendering. It is the only backend that supports COLR/CPAL color glyphs and fvar variable font axes.

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