DirectWrite API Reference

Windows Graphics and Multimedia > DirectWrite

Overview

DirectWrite is a high-performance, high-quality, GPU-accelerated text rendering API for Windows. It provides APIs for drawing text, formatting, and font management, enabling rich typography and text layout capabilities in your applications.

Core Concepts

Text Layout: Handling complex text shaping, bidirectional text, international scripts, and text wrapping.
Font Management: Enumerating system fonts, accessing font properties, and using font collections.
Text Rendering: Generating high-quality glyphs for display on screen or print.
Text Effects: Applying various effects like anti-aliasing, gamma correction, and subpixel rendering.

Interfaces

DirectWrite provides a set of interfaces for interacting with its features. Here are some of the most commonly used:

Interface	Description
IDWriteFactory	The primary interface for creating other DirectWrite objects.
IDWriteTextFormat	Represents text formatting properties like font family, size, weight, style, and paragraph alignment.
IDWriteTextLayout	Represents a block of text with layout properties applied, allowing for rich text manipulation.
IDWriteTypography	Enables control over OpenType typography features.
IDWriteInlineObject	Represents inline objects within text, such as images or other graphical elements.

Structures

Various structures are used to pass parameters and return information from DirectWrite functions.

Structure	Description
DWRITE_TEXT_METRICS	Contains text layout metrics such as width, height, and line count.
DWRITE_FONT_METRICS	Provides font metrics like ascent, descent, and units per em.
DWRITE_GLYPH_METRICS	Contains metrics for individual glyphs.

Enumerations

Enumerations define a set of constants used to specify options and states.

Enumeration	Description
DWRITE_FONT_WEIGHT	Specifies the weight (boldness) of a font.
DWRITE_FONT_STYLE	Specifies the style (italic, oblique) of a font.
DWRITE_TEXT_ALIGNMENT	Specifies horizontal text alignment within a paragraph.
DWRITE_PARAGRAPH_ALIGNMENT	Specifies vertical text alignment within a paragraph.

Functions

Key functions for creating and managing DirectWrite objects.

Creating the Factory:

HRESULT DWriteCreateFactory(
    DWRITE_FACTORY_TYPE factoryType,
    const IID& iid,
    _COM_Outptr_ IUnknown** factory
);

This function creates an instance of the DirectWrite factory.

Creating Text Formats:

HRESULT CreateTextFormat(
    const WCHAR* fontFamilyName,
    IDWriteFontCollection* fontCollection,
    DWRITE_FONT_WEIGHT fontWeight,
    DWRITE_FONT_STYLE fontStyle,
    DWRITE_FONT_STRETCH fontStretch,
    FLOAT fontSize,
    const WCHAR* localeName,
    _Outptr_ IDWriteTextFormat** textFormat
);

Creates an IDWriteTextFormat object with specified font properties.

Rendering Text:

Text is typically rendered using Direct2D's ID2D1RenderTarget::DrawTextLayout method, passing an IDWriteTextLayout object.