annotate build/README.osx @ 481:8701366604c7

Update a couple of comments to match the specifications elsewhere

The Vamp Plugin SDK -- Platform Notes for OS/X
==============================================

Prerequisites
-------------

You must have Xcode installed, with the command-line build tools (an
optional component).

You must have libsndfile (http://www.mega-nerd.com/libsndfile/)
installed in order to build the command-line host successfully.  But
you do not need libsndfile if you only want to build plugins.


Building at the command line
----------------------------

To build the SDK, example plugins, and command-line host:

 $ make -f build/Makefile.osx

To build only the SDK and example plugins (for example if you do not
have libsndfile installed):

 $ make -f build/Makefile.osx sdk plugins

See the comments at the top of Makefile.osx for more information about
the libraries and other targets that are built in this way.

If you are using an IDE such as Xcode, you may prefer to add the
vamp-sdk and src/vamp-sdk (for plugins) or vamp-hostsdk and
src/vamp-hostsdk (for hosts) directories to your existing project.

If you are using OS/X 10.6 or older, you could try Makefile.osx.106
instead of Makefile.osx.


Installing the Example Plugins
------------------------------

To install the example plugins so you can load them in Vamp hosts,
copy the files

   examples/vamp-example-plugins.dylib
and
   examples/vamp-example-plugins.cat

to
   /Library/Audio/Plug-Ins/Vamp/
or 
   $HOME/Library/Audio/Plug-Ins/Vamp/


Plugin Linkage
--------------

Vamp plugins are distributed as dynamic libraries (.dylib).  An OS/X
dynamic library has a formal installed name, which is recorded in the
library's header: you will need to ensure that this matches the
plugin's filename (e.g. vamp-example-plugins.dylib) by using the
-install_name <name> option at link time.  The Makefile.osx provided
with the SDK contains an example of this.

A well-packaged Vamp plugin library should export exactly one public
symbol, namely the Vamp API entry point vampGetPluginDescriptor.

The default for the OS/X linker is to export all of the symbols in the
library.  This will work (the host will be able to load the plugin),
but it unnecessarily pollutes the host's symbol namespace, it may
cause symbol collisions in some esoteric circumstances, and it
increases the amount of time the plugin takes to load.

To improve this behaviour, you can instruct the linker to export only
the one required symbol using a symbols list file.  To do this, place
the single line

_vampGetPluginDescriptor

(with leading underscore) into a text file, and then use the
-exported_symbols_list option to the linker to tell it to refer to
this file.  All other symbols will then be properly hidden.

The Makefile.osx included in this SDK uses this method to manage
symbol visibility for the included example plugins, using the file
build/vamp-plugin.list.  There are other methods that will work too,
but this one is simple and has the advantage of requiring no changes
to the code.


Test Your Plugins
-----------------

The Vamp Plugin Tester is a vital utility which you can use to test
your plugins for common problems.  It can help you if you're having
problems getting your plugin to work at all, and you're strongly
advised to use it before you release anything.  Download it from the
Vamp plugins site now!