This document provides details on the design and implementation of the FreeType 2 library. Its goal is to help developers better understand how FreeType 2 is organized, in order to let them extend, customize, and debug it.
Before anything else, it is important to understand the purpose of this library, i.e., why it has been written.
It allows client applications to access font files easily, wherever they could be stored, and as independently of the font format as possible.
Easy retrieval of global font data most commonly found in normal font formats (i.e., global metrics, encoding/charmaps, etc.).
It allows easy retrieval of individual glyph data (metrics, images, name, anything else).
Access to font format-specific ‘features’ whenever possible (e.g., SFNT tables, Multiple Masters, OpenType layout tables, font variations, etc.).
Its design has also severely been influenced by the following requirements.
High portability. The library must be able to run on any kind of environment. This requirement introduces a few drastic choices that are part of FreeType 2's low-level system interface.
Extendability. New features should be added with the least modifications in the library's code base. This requirement induces an extremely simple design where nearly all operations are provided by modules or services.
Customization. It should be easy to build a version of the library that only contains the features needed by a specific project. This really is important when you need to integrate it into a font server for embedded graphics libraries, say.
Compactness and efficiency. The primary target for this library originally were embedded systems with low CPU and memory resources. Today, however, memory constraints are much less strict, and the focus of development shifted to support as much font features as possible.
The rest of this document is divided in several sections. First, a few chapters will present the library's basic design as well as the objects and data managed internally by FreeType 2.
It is intended to eventually add sections that cover library customization, relating to topics as system-specific interfaces, how to write your own modules or services and how to tailor library initialization and compilation to your needs. Those sections are not written yet, however.
Last update: 13-Feb-2018