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DirectWrite Rasterizer

DirectWrite rasterizer backend using TerraFX.Interop.Windows bindings. Provides access to Windows' modern text rendering APIs, including ClearType-hinted grayscale rendering and system font loading.

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,
    Backend = RasterizerBackend.DirectWrite
};

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

For system fonts, use GenerateFromSystem:

var result = BmFont.GenerateFromSystem("Segoe UI", new FontGeneratorOptions
{
    Size = 32,
    Backend = RasterizerBackend.DirectWrite
});
Note

Color font (ColorPaletteIndex) and variable font (VariationAxes) options are not yet honored by this backend -- see Limitations. Use FreeType for COLR/CPAL and fvar today.

Capabilities

  • ClearType-hinted grayscale 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

  • Color fonts (COLR/CPAL) are not yet implemented -- the capability is currently stubbed (SupportsColorFonts returns false; there is no TranslateColorGlyphRun implementation yet). Use FreeType for color glyphs.
  • Variable font axes (fvar) are not yet implemented -- the capability is currently stubbed (SupportsVariableFonts returns false; there is no IDWriteFontFace5 axis implementation yet). Use FreeType for variable fonts.
  • 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 vector outlines (OutlineMode.Vector falls back to core's bitmap outline effect, which works as usual), and no WidthPercent or non-default ItalicAngle (NotSupportedException)

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 want Windows' ClearType-hinted grayscale rendering or need to load system-installed fonts by family name on Windows. For color fonts (COLR/CPAL) or variable font axes (fvar), use FreeType -- those DirectWrite code paths are currently stubbed and not yet functional.

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