/*!
\mainpage Welcome to the Haiku Book
Below you will find documentation on the Application Programming
Interface (API) of the Haiku operating system. This API describes
the internals of the operating system allowing developers to write
native C++ applications and device drivers. See the
online version for the most
updated version of this document. If you would like to help contribute
contact the documentation
mailing list. For guidelines on how to help document the API see
the \link apidoc Documenting the API\endlink page. A list of
contributors can be found \ref credits page. Documenting the API is
an ongoing process so contributions are greatly appreciated.
The Haiku API is based on the BeOS R5 API but changes and additions have
been included where appropriate. Important compatibility differences are
detailed on the \ref compatibility page. New classes and methods
and incompatible API changes to the BeOS R5 API are noted in the
appropriate sections.
A complete reference to the BeOS R5 API is available on the web in
The Be Book.
The Be Book is used with permission from
Access Co., the current
owners of Be's intellectual property.
\section kits Kits and Servers
The API is split into several kits and servers each detailing a different
aspect of the operating system.
- The \ref app is the starting point for developing applications
and includes classes for messaging and for interacting with
the rest of the system.
- The \ref game provides classes for producing game sounds and
working with full screen apps.
- The \ref interface is used to create responsive and attractive
graphical user interfaces building on the messaging facilities
provided by the Application Kit.
- The \link layout_intro Layout API \endlink is a new addition
to the Interface Kit in Haiku which provides resources to
layout your application flexibly and easily.
- The \ref locale includes classes to localize your application to
different languages, timezones, number formatting conventions and
much more.
- The \ref media provides a unified and consistent interface for media
streams and applications to intercommunicate.
- The \ref midi2 describes an interface to generating, processing,
and playing music in MIDI format. For reference documentation on the
\ref midi1 is also included.
- The \ref network handles everything network related, from interface
IP address settings to HTTP connections.
- The \ref storage is a collection of classes that deal with storing and
retrieving information from disk.
- The \ref support contains support classes to use in your application
including resources for thread safety, IO, and serialization.
- The \ref translation provides a framework for converting data streams
between media formats.
\section special_topics Special Topics
- \ref drivers
- \ref keyboard
*/
///// Define main kits /////
/*!
\defgroup app Application Kit
\brief The Application Kit is the starting point for writing native Haiku
GUI applications.
The application kit is exactly what its name suggests — it is the
basis of Haiku applications. You should first read through this document
and the references here before moving on to the other parts of the API.
The Application Kit classes can be divided into two groups: the messaging
classes and the system interaction classes. The larger of the two groups is
the messaging classes. Since the Haiku API relies on pervasive
multithreading messaging is an essential topic for any application. Have a
look at the \link app_messaging Introduction to Messaging \endlink for more
information.
The following messaging classes which allow you to easily and securely
communicate between threads.
- BHandler
- BInvoker
- BLooper
- BMessage
- BMessageFilter
- BMessageQueue
- BMessageRunner
- BMessenger
The second group is the system interaction classes. These classes
provide hooks for your application to interact with the rest of the system.
The most important class in this group is BApplication. Below is a list of
all system interaction classes:
- BApplication
- BClipboard
- BCursor
- BPropertyInfo
- BRoster
\defgroup game Game Kit
\brief The Game Kit provides classes for producing game sounds and
working with full screen apps.
\defgroup interface Interface Kit
\brief API for displaying a graphical user interface.
The Interface Kit holds all the classes you'll need to develop a GUI.
Building on the messaging facilities provided by the Application Kit,
the Interface Kit can be used to create a responsive and attractive
graphical user interface.
The most important class in the Interface Kit is the BView class, which
handles drawing and user interaction. Pointer and keyboard events are
processed in this class.
Another important class is the BWindow class, which holds BViews and makes
them visible to the user. The BWindow class also handles BView focusing
and BMessage dispatching, among other things.
A new addition Haiku has added over the BeOS API is the Layout API, which
is based around the BLayoutItem and BLayout classes. These classes will
take care of making sure all your GUI widgets end up where you want them,
with enough space to be useful. You can start learning the Layout API
by reading the \link layout_intro introduction \endlink.
\defgroup locale Locale Kit
\brief Collection of classes for localizing applications.
The Locale Kit provides a set of tools for internationalizing,
localizing and translating your software. This includes not only
replacing string with their translations at runtime, but also more
complex tasks such as formatting numbers, dates, and times in a way
that match the locale preferences of the user.
The main way to access locale data is through the be_locale_roster.
This is a global instance of the BLocaleRoster class, storing the data
for localizing an application according to the user's preferred settings.
The locale roster also acts as a factory to instantiate most of the other
classes. However, there are some cases where you will need to instantiate
another class by yourself, to use it with custom settings. For example, you
may need to format a date with a fixed format in english for including in an
e-mail header, as it is the only format accepted there.
Unlike the other kits in Haiku, the Locale kit does not live in libbe.
When building a localized application, you have to link it to
liblocale.so. If you want to use the catalog macros, you also have to
link each of your images (that is, applications, libraries and add-ons)
to liblocalestub.a.
\defgroup media Media Kit
\brief Collection of classes that deal with audio and video.
\defgroup midi1 The old MIDI Kit (libmidi.so)
\brief The old MIDI kit.
\defgroup midi2 MIDI 2 Kit
\brief The Midi Kit is the API that implements support for generating,
processing, and playing music in MIDI format.
MIDI, which stands for 'Musical
Instrument Digital Interface', is a well-established standard for
representing and communicating musical data. This document serves as
an overview. If you would like to see all the components, please look
at \link midi2 the list with classes \endlink.
\section midi2twokits A Tale of Two MIDI Kits
BeOS comes with two different, but compatible Midi Kits. This
documentation focuses on the "new" Midi Kit, or midi2 as we like to
call it, that was introduced with BeOS R5. The old kit, which we'll
refer to as midi1, is more complete than the new kit, but less powerful.
Both kits let you create so-called MIDI endpoints, but the endpoints
from midi1 cannot be shared between different applications. The midi2
kit solves that problem, but unlike midi1 it does not include a General
MIDI softsynth, nor does it have a facility for reading and playing
Standard MIDI Files. Don't worry: both kits are compatible and you can
mix-and-match them in your applications.
The main differences between the two kits:
- Instead of one BMidi object that both produces and consumes events,
we have BMidiProducer and BMidiConsumer.
- Applications are capable of sharing MIDI producers and consumers
with other applications via the centralized Midi Roster.
- Physical MIDI ports are now sharable without apps "stealing" events
from each other.
- Applications can now send/receive raw MIDI byte streams (useful if
an application has its own MIDI parser/engine).
- Channels are numbered 0–15, not 1–16
- Timing is now specified in microseconds rather than milliseconds.
\section midi2concepts Midi Kit Concepts
A brief overview of the elements that comprise the Midi Kit:
- \b Endpoints. This is what the Midi Kit is all about: sending MIDI
messages between endpoints. An endpoint is like a MIDI In or MIDI
Out socket on your equipment; it either receives information or it
sends information. Endpoints that send MIDI events are called
\b producers; the endpoints that receive those events are called
\b consumers. An endpoint that is created by your own application
is called \b local; endpoints from other applications are
\b remote. You can access remote endpoints using \b proxies.
- \b Filters. A filter is an object that has a consumer and a producer
endpoint. It reads incoming events from its consumer, performs some
operation, and tells its producer to send out the results. In its
current form, the Midi Kit doesn't provide any special facilities
for writing filters.
- \b Midi \b Roster. The roster is the list of all published producers
and consumers. By publishing an endpoint, you allow other
applications to talk to it. You are not required to publish your
endpoints, in which case only your own application can use them.
- \b Midi \b Server. The Midi Server does the behind-the-scenes work.
It manages the roster, it connects endpoints, it makes sure that
endpoints can communicate, and so on. The Midi Server is started
automatically when BeOS boots, and you never have to deal with it
directly. Just remember that it runs the show.
- \b libmidi. The BMidi* classes live inside two shared libraries:
libmidi.so and libmidi2.so. If you write an application that uses
old Midi Kit, you must link it to libmidi.so. Applications that use
the new Midi Kit must link to libmidi2.so. If you want to
mix-and-match both kits, you should also link to both libraries.
Here is a pretty picture:
\image html midi2concepts.png
\section midi2mediakit Midi Kit != Media Kit
Be chose not to integrate the Midi Kit into the Media Kit as another media
type, mainly because MIDI doesn't require any of the format negotiation that
other media types need. Although the two kits look similar -- both have a
"roster" for finding or registering "consumers" and "producers" -- there are
some very important differences.
The first and most important point to note is that BMidiConsumer and
BMidiProducer in the Midi Kit are \b NOT directly analogous to
BBufferConsumer and BBufferProducer in the Media Kit! In the Media Kit,
consumers and producers are the data consuming and producing properties
of a media node. A filter in the Media Kit, therefore, inherits from both
BBufferConsumer and BBufferProducer, and implements their virtual member
functions to do its work.
In the Midi Kit, consumers and producers act as endpoints of MIDI data
connections, much as media_source and media_destination do in the Media Kit.
Thus, a MIDI filter does not derive from BMidiConsumer and BMidiProducer;
instead, it contains BMidiConsumer and BMidiProducer objects for each of its
distinct endpoints that connect to other MIDI objects. The Midi Kit does not
allow the use of multiple virtual inheritance, so you can't create an object
that's both a BMidiConsumer and a BMidiProducer.
This also contrasts with the old Midi Kit's conception of a BMidi object,
which stood for an object that both received and sent MIDI data. In the new
Midi Kit, the endpoints of MIDI connections are all that matters. What lies
between the endpoints, i.e. how a MIDI filter is actually structured, is
entirely at your discretion.
Also, rather than use token structs like media_node to make connections
via the MediaRoster, the new kit makes the connections directly via the
BMidiProducer object.
\section midi2remotelocal Remote vs. Local Objects
The Midi Kit makes a distinction between remote and local MIDI objects.
You can only create local MIDI endpoints, which derive from either
BMidiLocalConsumer or BMidiLocalProducer. Remote endpoints are endpoints
that live in other applications, and you access them through BMidiRoster.
BMidiRoster only gives you access to BMidiEndpoints, BMidiConsumers, and
BMidiProducers. When you want to talk to remote MIDI objects, you do so
through the proxy objects that BMidiRoster provides. Unlike
BMidiLocalConsumer and BMidiLocalProducer, these classes do not provide a
lot of functions. That is intentional. In order to hide the details of
communication with MIDI endpoints in other applications, the Midi Kit must
hide the details of how a particular endpoint is implemented.
So what can you do with remote objects? Only what BMidiConsumer,
BMidiProducer, and BMidiEndpoint will let you do. You can connect
objects, get the properties of these objects -- and that's about it.
\section midi2lifespan Creating and Destroying Objects
The constructors and destructors of most midi2 classes are private,
which means that you cannot directly create them using the C++
new
operator, on the stack, or as globals. Nor can you
delete
them. Instead, these objects are obtained through
BMidiRoster. The only two exceptions to this rule are BMidiLocalConsumer
and BMidiLocalProducer. These two objects may be directly created and
subclassed by developers.
\section midi2refcount Reference Counting
Each MIDI endpoint has a reference count associated with it, so that
the Midi Roster can do proper bookkeeping. When you construct a
BMidiLocalProducer or BMidiLocalConsumer endpoint, it starts with a
reference count of 1. In addition, BMidiRoster increments the reference
count of any object it hands to you as a result of
\link BMidiRoster::NextEndpoint() NextEndpoint() \endlink or
\link BMidiRoster::FindEndpoint() FindEndpoint() \endlink.
Once the count hits 0, the endpoint will be deleted.
This means that, to delete an endpoint, you don't call the
delete
operator directly; instead, you call
\link BMidiEndpoint::Release() Release() \endlink.
To balance this call, there's also an
\link BMidiEndpoint::Acquire() Acquire() \endlink, in case you have two
disparate parts of your application working with the endpoint, and you
don't want to have to keep track of who needs to Release() the endpoint.
When you're done with any endpoint object, you must Release() it.
This is true for both local and remote objects. Repeat after me:
Release() when you're done.
\section midi2events MIDI Events
To make some actual music, you need to
\link BMidiProducer::Connect() Connect() \endlink your consumers to
your producers. Then you tell the producer to "spray" MIDI events to all
the connected consumers. The consumers are notified of these incoming
events through a set of hook functions.
The Midi Kit already provides a set of commonly used spray functions,
such as \link BMidiLocalProducer::SprayNoteOn() SprayNoteOn() \endlink,
\link BMidiLocalProducer::SprayControlChange() SprayControlChange()
\endlink, and so on. These correspond one-to-one with the message types
from the MIDI spec. You don't need to be a MIDI expert to use the kit, but
of course some knowledge of the protocol helps. If you are really hardcore,
you can also use the
\link BMidiLocalProducer::SprayData() SprayData() \endlink to send raw MIDI
events to the consumers.
At the consumer side, a dedicated thread invokes a hook function for every
incoming MIDI event. For every spray function, there is a corresponding hook
function, e.g. \link BMidiLocalConsumer::NoteOn() NoteOn() \endlink and
\link BMidiLocalConsumer::ControlChange() ControlChange() \endlink.
The hardcore MIDI fanatics among you will be pleased to know that you can
also tap into the \link BMidiLocalConsumer::Data() Data() \endlink hook and
get your hands dirty with the raw MIDI data.
\section midi2time Time
The spray and hook functions accept a bigtime_t parameter named "time". This
indicates when the MIDI event should be performed. The time is given in
microseconds since the computer booted. To get the current tick measurement,
you call the system_time() function from the Kernel Kit.
If you override a hook function in one of your consumer objects, it should
look at the time argument, wait until the designated time, and then perform
its action. The preferred method is to use the Kernel Kit's
snooze_until()
function, which sends the consumer thread to
sleep until the requested time has come. (Or, if the time has already
passed, returns immediately.)
Like this:
\code
void MyConsumer::NoteOn(
uchar channel, uchar note, uchar velocity, bigtime_t time)
{
snooze_until(time, B_SYSTEM_TIMEBASE);
...do your thing...
}
\endcode
If you want your producers to run in real time, i.e. they produce MIDI data
that needs to be performed immediately, you should pass time 0 to the spray
functions (which also happens to be the default value). Since time 0 has
already passed, snooze_until()
returns immediately, and the
consumer will process the events as soon as they are received.
To schedule MIDI events for a performance time that lies somewhere in the
future, the producer must take into account the consumer's latency.
Producers should attempt to get notes to the consumer by or before
(scheduled_performance_time - latency). The time argument is still
the scheduled performance time, so if your consumer has latency, it should
snooze like this before it starts to perform the events:
\code
snooze_until(time - Latency(), B_SYSTEM_TIMEBASE);
\endcode
Note that a typical producer sends out its events as soon as it can;
unlike a consumer, it does not have to snooze.
\section midi2ports Other Timing Issues
Each consumer object uses a Kernel Kit port to receive MIDI events from
connected producers. The queue for this port is only 1 message deep.
This means that if the consumer thread is asleep in a
snooze_until()
, it will not read its port. Consequently,
any producer that tries to write a new event to this port will block until
the consumer thread is ready to receive a new message. This is intentional,
because it prevents producers from generating and queueing up thousands of
events.
This mechanism, while simple, puts on the producer the responsibility
for sorting the events in time. Suppose your producer sends three Note
On events, the first on t + 0, the second on t + 4, and the third on t + 2.
This last event won't be received until after t + 4, so it will be two ticks
too late. If this sort of thing can happen with your producer, you should
somehow sort the events before you spray them. Of course, if you have two or
more producers connected to the same consumer, it is nearly impossible to
sort this all out (pardon the pun). So it is not wise to send the same kinds
of events from more than one producer to one consumer at the same time.
The article Introduction to MIDI, Part 2 in OpenBeOS
Newsletter 36 describes this problem in more detail, and provides a
solution. Go read it now!
\section midi2filters Writing a Filter
A typical filter contains a consumer and a producer endpoint. It receives
events from the consumer, processes them, and sends them out again using the
producer. The consumer endpoint is a subclass of BMidiLocalConsumer, whereas
the producer is simply a BMidiLocalProducer, not a subclass. This is a
common configuration, because consumers work by overriding the event hooks
to do work when MIDI data arrives. Producers work by sending an event when
you call their member functions. You should hardly ever need to derive from
BMidiLocalProducer (unless you need to know when the producer gets connected
or disconnected, perhaps), but you'll always have to override one or more of
BMidiLocalConsumer's member functions to do something useful with incoming
data.
Filters should ignore the time argument from the spray and hook functions,
and simply pass it on unchanged. Objects that only filter data should
process the event as quickly as possible and be done with it. Do not
snooze_until()
in the consumer endpoint of a filter!
\section midi2apidiffs API Differences
As far as the end user is concerned, the Haiku Midi Kit is mostly the same
as the BeOS R5 kits, although there are a few small differences in the API
(mostly bug fixes):
- BMidiEndpoint::IsPersistent() always returns false.
- The B_MIDI_CHANGE_LATENCY notification is now properly sent. The Be
kit incorrectly set be:op to B_MIDI_CHANGED_NAME, even though the
rest of the message was properly structured.
- If creating a local endpoint fails, you can still Release() the object
without crashing into the debugger.
\section midi2seealso See also
More about the Midi Kit:
- \ref Midi2Defs.h
- Be Newsletter Volume 3, Issue 47 - Motor Mix sample code
- Be Newsletter Volume 4, Issue 3 - Overview of the new kit
- Newsletter
33, Introduction to MIDI, Part 1
- Newsletter
36, Introduction to MIDI, Part 2
- Sample code and other goodies at the
Haiku Midi Kit team page
Information about MIDI in general:
- MIDI Manufacturers Association
- MIDI Tutorials
- MIDI Specification
- Standard MIDI File Format
- Jim Menard's MIDI Reference
\defgroup libmidi2 (libmidi2.so)
\defgroup network Network Kit
\brief Classes that deal with all network connections and communications.
\defgroup storage Storage Kit
\brief Collection of classes that deal with storing and retrieving
information from disk.
\defgroup support Support Kit
\brief Collection of utility classes that are used throughout the API.
The Support Kit provides a handy set of classes that you can use in your
applications. These classes provide:
- \b Thread \b Safety. Haiku can execute multiple threads of an
application in parallel, letting certain parts of an application
continue when one part is stalled, as well as letting an application
process multiple pieces of data at the same time on multicore or
multiprocessor systems. However, there are times when multiple
threads desire to work on the same piece of data at the same time,
potentially causing a conflict where variables or pointers are
changed by one thread causing another to execute incorrectly. To
prevent this, Haiku implements a \"locking\" mechanism, allowing one
thread to \"lock out\" other threads from executing code that might
modify the same data.
- \b Archiving \b and \b IO. These classes allow a programmer to
convert objects into a form that can more easily be transferred to
other applications or stored to disk, as well as performing basic
input and output operations.
- \b Memory \b Allocation. This class allows a programmer to hand off
some of the duties of memory accounting and management.
- \b Common \b Datatypes. To avoid unnecessary duplication of code
and to make life easier for programmers, Haiku includes classes that
handle management of ordered lists and strings.
There are also a number of utility functions to time actions, play system
alert sounds, compare strings, and atomically manipulate integers. Have a
look at the overview, or go straight to the complete
\link support list of components \endlink of this kit.
\section Overview
- Thread Safety:
- BLocker provides a semaphore-like locking mechanism allowing for
recursive locks.
- BAutolock provides a simple method of automatically removing a
lock when a function ends.
- \ref TLS.h "Thread Local Storage" allows a global variable\'s
content to be sensitive to thread context.
- Archiving and IO:
- BArchivable provides an interface for \"archiving\" objects so
that they may be sent to other applications where an identical
copy will be recreated.
- BArchiver simplifies archiving of BArchivable hierarchies.
- BUnarchiver simplifies unarchiving hierarchies that have been
archived using BArchiver.
- BFlattenable provides an interface for \"flattening\" objects so
that they may be easily stored to disk.
- BDataIO provides an interface for generalized read/write streams.
- BPositionIO extends BDataIO to allow seeking within the data.
- BBufferIO creates a buffer and attaches it to a BPositionIO
stream, allowing for reduced load on the underlying stream.
- BMemoryIO allows operation on an already-existing buffer.
- BMallocIO creates and allows operation on a buffer.
- Memory Allocation:
- BBlockCache allows an application to allocate a \"pool\" of
memory blocks that the application can fetch and dispose of as
it pleases, letting the application make only a few large memory
allocations, instead of many small expensive allocations.
- Common Datatypes:
- BList allows simple ordered lists and provides common access,
modification, and comparison functions.
- BString allows strings and provides common access, modification,
and comparison functions.
- BStopWatch allows an application to measure the time an action takes.
- \ref support_globals "Global functions"
- \ref TypeConstants.h "Common types and constants"
- Error codes for all kits
\defgroup translation Translation Kit
\brief Provides a framework for converting data streams between media
formats.
\defgroup libbe (libbe.so)
\defgroup libroot (libroot.so)
*/
///// Subgroups /////
/*!
\defgroup support_globals Global functions in the support kit
\ingroup support
\defgroup layout Layout classes in the Interface Kit
\ingroup interface
*/
///// Special Topics /////
\defgroup drivers Device Drivers
\defgroup keyboard Keyboard