JUCE/docs/JUCE Module Format.md

The JUCE Module Format

A JUCE module is a collection of header and source files which can be added to a project to provide a set of classes and libraries or related functionality.

Their structure is designed to make it as simple as possible for modules to be added to user projects on many platforms, either via automated tools, or by manual inclusion.

Each module may have dependencies on other modules, but should be otherwise self-contained.

File structure

Each module lives inside a folder whose name is the same as the name of the module. The JUCE convention for naming modules is lower-case with underscores, e.g.

juce_core
juce_events
juce_graphics

But any name that is a valid C++ identifer is OK.

Inside the root of this folder, there must be a set of public header and source files which the user's’ project will include. The module may have as many other internal source files as it needs, but these must all be inside sub-folders!

Master header file

In this root folder there must be ONE master header file, which includes all the necessary header files for the module. This header must have the same name as the module, with a .h/.hpp/.hxx suffix. E.g.

juce_core/juce_core.h

IMPORTANT! All code within a module that includes other files from within its own subfolders must do so using RELATIVE paths! A module must be entirely relocatable on disk, and it must not rely on the user's project having any kind of include path set up correctly for it to work. Even if the user has no include paths whatsoever and includes the module's master header via an absolute path, it must still correctly find all of its internally included sub-files.

This master header file must also contain a comment with a BEGIN_JUCE_MODULE_DECLARATION block which defines the module's requirements - the syntax for this is described later on..

Module CPP files

A module consists of a single header file and zero or more .cpp files. Fewer is better!

Ideally, a module could be header-only module, so that a project can use it by simply including the master header file.

For various reasons it's usually necessary or preferable to have a simpler header and some .cpp files that the user's project should compile as stand-alone compile units. In this case you should ideally provide just a single cpp file in the module's root folder, and this should internally include all your other cpps from their sub-folders, so that only a single cpp needs to be added to the user's project in order to completely compile the module.

In some cases (e.g. if your module internally relies on 3rd-party code which can't be easily combined into a single compile-unit) then you may have more than one source file here, but avoid this if possible, as it will add a burden for users who are manually adding these files to their projects.

The names of these source files must begin with the name of the module, but they can have a number or other suffix if there is more than one.

In order to specify that a source file should only be compiled on a specific platform, then the filename can be suffixed with one of the following strings:

_OSX
_Windows
_Linux
_Android
_iOS

e.g.

juce_mymodule/juce_mymodule_1.cpp         <- compiled on all platforms
juce_mymodule/juce_mymodule_2.cpp         <- compiled on all platforms
juce_mymodule/juce_mymodule_OSX.cpp       <- compiled only on OSX
juce_mymodule/juce_mymodule_Windows.cpp   <- compiled only on Windows

Often this isn't necessary, as in most cases you can easily add checks inside the files to do different things depending on the platform, but this may be handy just to avoid clutter in user projects where files aren't needed.

To simplify the use of obj-C++ there's also a special-case rule: If the folder contains both a .mm and a .cpp file whose names are otherwise identical, then on OSX/iOS the .mm will be used and the cpp ignored. (And vice-versa for other platforms, of course).

Precompiled libraries

Precompiled libraries can be included in a module by placing them in a libs/ subdirectory. The following directories are automatically added to the library search paths, and libraries placed in these directories can be linked with projects via the OSXLibs, iOSLibs, windowsLibs, linuxLibs and mingwLibs keywords in the module declaration (see the following section).

• OS X

  • libs/MacOSX - to support multiple architectures, you may place libraries built as universal binaries at this location. For backwards compatibility, the Projucer will also include the directories libs/MacOSX/{arch}, where {arch} is the architecture you are targeting in Xcode (“x86_64” or “i386”, for example). When building with CMake, only libraries built as universal binaries are supported and the arch subfolders are ignored.

• Visual Studio

  • libs/VisualStudio{year}/{arch}/{run-time}, where {year} is the four digit year of the Visual Studio release, arch is the target architecture in Visual Studio (“x64” or “Win32”, for example), and {runtime} is the type of the run-time library indicated by the corresponding compiler flag (“MD”, “MDd”, “MT”, “MTd”).

• Linux

  • libs/Linux/{arch}, where {arch} is the architecture you are targeting with the compiler. Some common examples of {arch} are “x86_64”, “i386” and “armv6”.

• MinGW

  • libs/MinGW/{arch}, where {arch} can take the same values as Linux.

• iOS

  • libs/iOS - to support multiple architectures, you may place libraries built as universal binaries at this location. For backwards compatibility, the Projucer will also include the directories libs/iOS/{arch}, where {arch} is the architecture you are targeting in Xcode (“arm64” or “x86_64”, for example). When building with CMake, only libraries built as universal binaries are supported and the arch subfolders are ignored.

• Android

  • libs/Android/{arch}, where {arch} is the architecture provided by the Android Studio variable “${ANDROID_ABI}” (“x86”, “armeabi-v7a”, “mips”, for example).

The BEGIN_JUCE_MODULE_DECLARATION block

This block of text needs to go inside the module's main header file. It should be commented-out and perhaps inside an #if 0 block too, but the Introjucer will just scan the whole file for the string BEGIN_JUCE_MODULE_DECLARATION, and doesn't care about its context in terms of C++ syntax.

The block needs a corresponding END_JUCE_MODULE_DECLARATION to finish the block. These should both be on a line of their own.

Inside the block, the parser will expect to find a list of value definitions, one-per-line, with the very simple syntax

value_name:   value

The value_name must be one of the items listed below, and is case-sensitive. Whitespace on the line is ignored. Some values are compulsory and must be supplied, but others are optional. The order in which they're declared doesn't matter.

Possible values:

• ID

  • (Compulsory) This ID must match the name of the file and folder, e.g. juce_core. The main reason for also including it here is as a sanity-check

• vendor

  • (Compulsory) A unique ID for the vendor, e.g. “juce”. This should be short and shouldn't contain any spaces

• version

  • (Compulsory) A version number for the module

• name

  • (Compulsory) A short description of the module

• description

  • (Compulsory) A longer description (but still only one line of text, please!)

• dependencies

  • (Optional) A list (space or comma-separated) of other modules that are required by this one. The Introjucer can use this to auto-resolve dependencies.

• website

  • (Optional) A URL linking to useful info about the module]

• license

  • (Optional) A description of the type of software license that applies

• minimumCppStandard

  • (Optional) A number indicating the minimum C++ language standard that is required for this module. This must be just the standard number with no prefix e.g. 14 for C++14

• searchpaths

  • (Optional) A space-separated list of internal include paths, relative to the module's parent folder, which need to be added to a project's header search path

• OSXFrameworks

  • (Optional) A list (space or comma-separated) of OSX frameworks that are needed by this module

• iOSFrameworks

  • (Optional) Like OSXFrameworks, but for iOS targets

• linuxPackages

  • (Optional) A list (space or comma-separated) pkg-config packages that should be used to pass compiler (CFLAGS) and linker (LDFLAGS) flags

• linuxLibs

  • (Optional) A list (space or comma-separated) of static or dynamic libs that should be linked in a linux build (these are passed to the linker via the -l flag)

• mingwLibs

  • (Optional) A list (space or comma-separated) of static libs that should be linked in a win32 mingw build (these are passed to the linker via the -l flag)

• OSXLibs

  • (Optional) A list (space or comma-separated) of static or dynamic libs that should be linked in an OS X build (these are passed to the linker via the -l flag)

• iOSLibs

  • (Optional) A list (space or comma-separated) of static or dynamic libs that should be linked in an iOS build (these are passed to the linker via the -l flag)

• windowsLibs

  • (Optional) A list (space or comma-separated) of static or dynamic libs that should be linked in a Visual Studio build (without the .lib suffixes)

Here's an example block:

BEGIN_JUCE_MODULE_DECLARATION

 ID:               juce_audio_devices
 vendor:           juce
 version:          4.1.0
 name:             JUCE audio and MIDI I/O device classes
 description:      Classes to play and record from audio and MIDI I/O devices
 website:          http://www.juce.com/juce
 license:          GPL/Commercial

 dependencies:     juce_audio_basics, juce_audio_formats, juce_events
 OSXFrameworks:    CoreAudio CoreMIDI DiscRecording
 iOSFrameworks:    CoreAudio CoreMIDI AudioToolbox AVFoundation
 linuxLibs:        asound
 mingwLibs:        winmm

END_JUCE_MODULE_DECLARATION