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Cross-Compiling FreeType

This document contains instructions on how to cross-build the FreeType library on Unix systems, for example, building binaries for Linux/MIPS on FreeBSD/i386. Before reading this document, please consult the file INSTALL_UNIX.md for required tools and the basic self-building procedure.

1. Required Tools

For self-building the FreeType library on a Unix system, GNU Make 3.81 or newer is required. [INSTALL_UNIX.md contains hints how to check the installed make.

The GNU C compiler to cross-build the target system is required. Currently, using a non-GNU cross compiler is untested. The cross compiler is expected to be installed with a system prefix. For example, if your building system is FreeBSD/i386 and the target system is Linux/MIPS, the cross compiler should be installed with the name mips-ip22-linuxelf-gcc.

A C compiler for a self-build is required also, to build a tool (apinames) that is executed during the build procedure. Non-GNU self compilers are acceptable, but such a setup is untested.

2. Configuration

2.1 Building and target system

To configure a cross-build, the options --host=<system> and --build=<system> must be passed to the configure script. For example, if your build system is FreeBSD/i386 and the target system is Linux/MIPS, say

  ./configure \
    --build=i386-unknown-freebsd \
    --host=mips-ip22-linuxelf \
    [other options]

It should be noted that --host=<system> specifies the system where the built binaries will be executed, not the system where the build actually happens. Older versions of GNU autoconf use the option pair --host= and --target=. This is broken and doesn't work. Similarly, an explicit CC specification like

  env CC=mips-ip22-linux-gcc ./configure                 # BAD

  env CC=/usr/local/mips-ip22-linux/bin/gcc ./configure  # BAD

doesn't work either; such a configuration confuses the configure script while trying to find the cross and native C compilers.

2.2. The prefix to install FreeType2

Setting --prefix=<prefix> properly is important. The prefix to install FreeType2 is written into the freetype-config script and freetype2.pc configuration file.

If the built FreeType 2 library is used as a part of the cross-building system, the prefix is expected to be different from the self-building system. For example, a configuration with --prefix=/usr/local installs binaries into the system-wide /usr/local directory, which then can't be executed due to the incorrect architecture. This causes confusion in configuration of all applications that use FreeType2. Instead, use a prefix to install the cross-build into a separate system tree, for example, --prefix=/usr/local/mips-ip22-linux/.

On the other hand, if the built FreeType 2 library is used as a part of the target system, the prefix to install should reflect the file system structure of the target system.

2.3. Library dependencies

FreeType normally depends on external libraries like libpng or libharfbuzz. The easiest case is to deactivate all such dependencies using the --without-XXX configuration options. However, if you want to use those libraries, you should ensure that they are available both on the target system and as (cross-compiled) libraries on the build system.

FreeType uses pkg-config to find most of the libraries; the other libraries it links to are expected in the standard system directories. Since the default pkg-config's meta-information files (like harfbuzz.pc) of the build platform don't work, use one of the two possible solutions below.

Use pkg-config's meta-information files that are adjusted to cross-compile and cross-link with the target platform's libraries. Make sure those files are found before the build system's default files. Example:
```
  ./configure \
    --build=i386-unknown-freebsd \
    --host=mips-ip22-linuxelf \
    PKG_CONFIG_LIBDIR="/usr/local/mips-ip22-linux/lib/pkgconfig" \
    [other options]
```
See the manpage of pkg-config for more details.

Set variables like LIBPNG_LIBS as additional options to the configure script, overriding the values pkg-config would provide. configure --help shows the available environment variables. Example:

  ./configure \
    --build=i386-unknown-freebsd \
    --host=mips-ip22-linuxelf \
    LIBPNG_CFLAGS="-I/usr/local/mips-ip22-linux/include" \
    LIBPNG_LIBS="-L/usr/local/mips-ip22-linux/lib -lpng12" \
    [other options]

3. Building command

If the configuration finishes successfully, invoking GNU make builds FreeType2. Just say

make

gmake

depending on the name the GNU make binary actually has.

4. Installation

Saying

make install

as usual to install FreeType2 into the directory tree specified by the argument of the --prefix option.

As noted in section 2.2, FreeType2 is sometimes configured to be installed into the system directory of the target system, and should not be installed in the cross-building system. In such cases, the make variable DESTDIR is useful to change the root directory in the installation. For example, after

  make DESTDIR=/mnt/target_system_root/ install

the built FreeType2 library files are installed into the directory /mnt/target_system_root/<prefix_in_configure>/lib.

5. TODO

Cross building between Cygwin (or MSys) and Unix must be tested.

Copyright (C) 2006-2023 by
suzuki toshiya, David Turner, Robert Wilhelm, and Werner Lemberg.

This file is part of the FreeType project, and may only be used,
modified, and distributed under the terms of the FreeType project
license, LICENSE.TXT. By continuing to use, modify, or distribute
this file you indicate that you have read the license and understand
and accept it fully.

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