DirectWrite Concepts

DirectWrite is a modern, hardware‑accelerated text layout and glyph rendering API designed for high‑quality text rendering in Windows applications. This guide covers the core concepts you need to create crisp, typographically correct text.

Text Layout

DirectWrite separates text measurement from rendering. The IDWriteTextLayout interface determines glyph placement, line breaking, and formatting based on the given text, font properties, and layout constraints.

// Create a text layout
IDWriteFactory* dwFactory = nullptr;
DWriteCreateFactory(DWRITE_FACTORY_TYPE_SHARED, __uuidof(IDWriteFactory), reinterpret_cast<IUnknown**>(&dwFactory));

IDWriteTextFormat* format = nullptr;
dwFactory->CreateTextFormat(L"Segoe UI", nullptr, DWRITE_FONT_WEIGHT_NORMAL,
    DWRITE_FONT_STYLE_NORMAL, DWRITE_FONT_STRETCH_NORMAL, 12.0f, L"en-us", &format);

IDWriteTextLayout* layout = nullptr;
dwFactory->CreateTextLayout(L"Hello DirectWrite!", 20, format, 300.0f, 200.0f,
    &layout);

Glyph Rendering

DirectWrite works with Direct2D or Direct3D to render glyphs. The IDWriteGlyphRunAnalysis object generates a bitmap or texture for each glyph run, supporting subpixel rendering, ClearType, and custom rasterization.

// Example of creating a glyph run analysis for ClearType rendering
IDWriteRenderingParams* renderParams = nullptr;
dwFactory->CreateRenderingParams(&renderParams);

IDWriteGlyphRunAnalysis* analysis = nullptr;
dwFactory->CreateGlyphRunAnalysis(&glyphRun, 1.0f, matrix, DWRITE_RENDERING_MODE_CLEARTYPE_NATURAL,
    DWRITE_MEASURING_MODE_NATURAL, 0.0f, 0.0f, &analysis);

Font Management

DirectWrite can enumerate installed fonts, create custom font collections, and retrieve font metrics. Use IDWriteFontCollection and IDWriteFontFamily to explore available font families.

// Enumerate system font families
IDWriteFontCollection* fontCollection = nullptr;
dwFactory->GetSystemFontCollection(&fontCollection, FALSE);
UINT32 familyCount = fontCollection->GetFontFamilyCount();

for (UINT32 i = 0; i < familyCount; ++i) {
    IDWriteFontFamily* family = nullptr;
    fontCollection->GetFontFamily(i, &family);
    // Retrieve family name...
    family->Release();
}

International Support

DirectWrite provides built‑in support for complex scripts, right‑to‑left languages, and Unicode line breaking. Enable these features through the IDWriteTextFormat properties such as DWRITE_TEXT_ALIGNMENT_JUSTIFY and DWRITE_READING_DIRECTION_RIGHT_TO_LEFT.

// Enable right‑to‑left reading direction
format->SetReadingDirection(DWRITE_READING_DIRECTION_RIGHT_TO_LEFT);
format->SetTextAlignment(DWRITE_TEXT_ALIGNMENT_LEADING);

Performance Tips