annotate plugin/api/alsa/README @ 961:fae5689f7e27

Frame this condition more defensively (from coverity scan)

libdssialsacompat 1.0.8a
========================
libdssialsacompat is simply an extraction from and repackaging of
the code from alsa-lib 1.0.8, necessary to support DSSI on non-ALSA
systems.  It is copyright (c)2005 under the GNU Lesser General
Public License, version 2.1 or later.  See the enclosed file COPYING
for details.

More information on DSSI can be found at:

  http://dssi.sourceforge.net/

Introduction
============
The DSSI specification makes use of the ALSA snd_seq_event_t
structure for passing MIDI events.  This has the advantage of making
it immediately familiar to developers familiar with ALSA, but the
disadvantage of making porting DSSI applications and plugins to
systems that lack ALSA more difficult.

libdssialsacompat is intended to provide the snd_seq_event_t
declarations and handling code necessary to compile and use DSSI on
non-ALSA systems.  It aims to allows compiling DSSI code with as
little change as possible, while not presenting itself in such a way
as to fool other autoconf-enabled code into thinking a system has
ALSA.

libdssialsacompat is simply an extraction of the relevant
snd_seq_event_t declarations, and raw MIDI stream to snd_seq_event_t
encoder code, from alsa-lib version 1.0.8, packaged into a
convenient library.

This library does NOT provide any sort of emulation of the ALSA
audio, MIDI, or sequencer devices.  The only part of ALSA that is
required by the DSSI specification is the snd_seq_event_t definition
and handling, and that is all libdssialsacompat is intended to
replace.  Other ALSA code should be ported to native facilities.

Installation
============
libdssialsacompat uses GNU autoconf and automake, so installation can
be a simple as `./configure && make && make install'.  See the
enclosed file INSTALL for more information.

The library itself is installed to <prefix>/lib; for example, on Mac
OS X, the following files are installed:

    <prefix>/lib/libdssialsacompat.0.0.0.dylib
    <prefix>/lib/libdssialsacompat.0.dylib
    <prefix>/lib/libdssialsacompat.a
    <prefix>/lib/libdssialsacompat.dylib
    <prefix>/lib/libdssialsacompat.la

The header files are installed to <prefix>/include/dssi/alsa:

    <prefix>/include/dssi/alsa/asoundef.h
    <prefix>/include/dssi/alsa/asoundlib.h
    <prefix>/include/dssi/alsa/seq.h
    <prefix>/include/dssi/alsa/seq_event.h
    <prefix>/include/dssi/alsa/seq_midi_event.h
    <prefix>/include/dssi/alsa/sound/asequencer.h

Note that they are NOT installed to <prefix>/include/alsa, which
could make them visible to non-libdssialsacompat-aware autoconf
configure scripts, possibly fooling them into thinking the full ALSA
was available.

Finally, a pkgconfig configuration file is installed:

    <prefix>/lib/pkgconfig/libdssialsacompat.pc

Use
===
At its most basic, compiling with gcc and libdssialsacompat consists
of adding '-I<prefix>/include/dssi -L<prefix>/lib -ldssialsacompat'
to your gcc command line.  Note that the '-I' directive will cause
code like to following:

    #include <alsa/asoundlib.h>
    #include <alsa/seq_event.h>

to find the libdssialsacompat header files, even though they are not
installed in the usual location for ALSA headers.

libdssialsacompat is easiest to use with autoconf/automake/pkgconfig-
enabled code.  In which case, editing the configure.in or configure.ac
file and changing:

    PKG_CHECK_MODULES(ALSA, alsa)

to:

    PKG_CHECK_MODULES(ALSA, alsa, , [PKG_CHECK_MODULES(ALSA, libdssialsacompat)])

then doing 'autoreconf', may be all that is needed to get the
snd_seq_event_t-using code to compile cleanly.  Of course, if the
code uses other ALSA features, libdssialsacompat won't help with
them....

DSSI Installation
=================
Installation of DSSI itself (at least as recently as 2005/4/6 CVS)
must be done by hand, which goes something like this (assuming
you're running OS X 10.3 and want to install to /usr/local):

$ tar xpzf dssi-0.9.tar.gz
$ cd dssi-0.9
$ sudo mkdir -p /usr/local/include
$ sudo cp dssi/dssi.h /usr/local/include/
$ sed s:.PREFIX.:/usr/local: dssi.pc >dssi.pc.new
$ sudo mkdir -p /usr/local/lib/pkgconfig
$ sudo mv dssi.pc.new /usr/local/lib/pkgconfig/dssi.pc

(You may stop here if you're not interested in the example plugins.)

$ cd examples
$ PKG_CONFIG_PATH=/usr/local/lib/pkgconfig
$ export PKG_CONFIG_PATH
$ make dssi_osc_send
$ sudo cp -p dssi_osc_send /usr/local/bin
$ gcc -Wall -fno-common -O2 `pkg-config libdssialsacompat dssi --cflags` \
    trivial_synth.c -c -o trivial_synth.o
$ gcc -Wall -fno-common -O2 -c -o message_buffer.o \
    ../message_buffer/message_buffer.c
$ gcc -bundle -flat_namespace -undefined suppress -o trivial_synth.so \
    trivial_synth.o message_buffer.o \
    `pkg-config libdssialsacompat dssi --libs`
$ sudo mkdir -p /usr/local/lib/dssi
$ sudo cp -p trivial_synth.so /usr/local/lib/dssi

Building the rest of the DSSI distribution's plugins is left as an
exercise to the reader.  Note that (as of 2005/4/6) jack-dssi-host
will not build without patching since it uses the ALSA sequencer.

What Works (Or Doesn't)
=======================
libdssialsacompat 1.0.8a was tested on Mac OS X 10.3.8, using the
Apple Developer Tools, Gentoo-installed versions of pkgconfig and
liblo 0.18, hand-installed GTK+ 1.2 and LADSPA SDK, and JackOSX
0.6.1.  Under this configuration, the following are known to work:

- ghostess (from the 20050411 release, which includes a clumsy but
    working CoreMIDI driver.)  ghostess can be found at:

    http://home.jps.net/~musound/

- trivial_synth.so (DSSI 0.9 release)

- fluidsynth-dssi.so and FluidSynth-DSSI_gtk (DSSI 0.9 release,
    using a statically compiled libfluidsynth 1.0.3)

- Xsynth-DSSI (CVS as of 2005/4/11)

- hexter (CVS as of 2005/4/11, note that sys-ex patch editing isn't
    supported on non-ALSA systems)

The following problems are known to exist:

- less_trivial_synth.so (DSSI 0.9) plays at the wrong pitch on
    big-endian systems due the little-endian assumption of the
    typedef union fixp in less_trivial_synth.c (line 69).  Otherwise
    works fine.

- I have not tested any of the DSSI 0.9 Qt GUIs, or
    trivial_sampler.so.

- jack-dssi-host (DSSI 0.9) works as an OSC-driven host if you
    comment out all the ALSA seqeuncer code.