4 \brief Defines consumer classes for the MIDI Kit.
9 \class BMidiConsumer MidiConsumer.h
11 \brief Receives MIDI events from a producer
13 A consumer is an object that knows how to deal with incoming MIDI events. A
14 consumer can be connected to multiple producers at the same time. There is no
15 way to find out which producers are connected to this consumer just by looking
16 at the BMidiConsumer object; you will have to consult BMidiRoster for that.
18 A BMidiConsumer either represents a local consumer, i.e. a class extending from
19 BMidiLocalConsumer, or is a proxy for a remote object published by another app.
24 \fn bigtime_t BMidiConsumer::Latency() const
25 \brief Returns the latency of this consumer
27 The latency is measured in microseconds. Producers should attempt to get MIDI
28 events to this consumer by <I>(when - latency)</I>. You do this by subtracting
29 the latency from the performance time when you spray the events (provided that
30 you spray these events ahead of time, of course).
32 You cannot <I>set</I> the latency on a BMidiConsumer, only on a
35 The latency issue gets slightly more complicated when multiple endpoints are
36 chained together, as in the following picture:
39 +-------+ +-------------+ +-------+
41 | prodA |---->| consB prodB |---->| consC |
43 +-------+ +-------------+ +-------+
44 appA appB (filter) appC
47 Suppose consC has 200ms latency, and consB has 100ms latency. If consB simply
48 reports 100ms, then prodA will schedule its events for (t - 100), which is
49 really 200ms too late. (Of course, producers send out their events as soon as
50 possible, so depending on the load of the system, everything may work out just
53 ConsB should report the latency of the consumer that is hooked up to its
54 output, consC, in addition to its own latency. In other words, the full
55 downstream latency. So, the reported latency in this case would be 300ms. This
56 also means that appB should change the latency of consB when prodB makes or
57 breaks a connection, and when consC reports a latency change. (If multiple
58 consumers are connected to prodB, you should take the slowest one.)
59 Unfortunately, the Midi Kit provides no easy mechanism for doing any of this,
60 so you are on your own here.
64 \class BMidiLocalConsumer MidiConsumer.h
66 \brief A consumer endpoint that is created by your own application.
68 If you want to create a consumer that reacts to MIDI events, you should
69 subclass BMidiLocalConsumer.
71 Each local consumer has its own thread that receives and dispatches the MIDI
72 events. Whenever MIDI data arrives, the Data() hook passes the MIDI event on to
73 a more specific hook function: NoteOn(), NoteOff(), SystemExclusive(), and so
74 on. Calls to these hook functions are serialized -- they will never have to be
75 re-entrant. They also should not be called from outside the thread that is
78 Your subclass can override any of the MIDI event hooks. BMidiLocalConsumer
79 doesn't provide default implementations for them, so you don't have to call a
80 hook's default implementation if you override it. For complete control, you can
83 Most hook functions take a channel argument. Even though MIDI channels are
84 really numbered 1 through 16, the hook functions work with channels 0 through
85 15. The performance time for the event is specified in microseconds relative to
86 the system time base. A performance time that is 0 (or really any time in the
87 past) means "play as soon as possible". See the \ref midi2time "introduction"
88 for more information about timing and consumers.
90 The thread driving the consumer's events is a very high priority real time
91 thread. Events should be handled as quickly as possible (not counting
92 snoozing). If non-time-critical computation is needed it may be wise to queue
93 events up for a lower priority thread to handle them external to the main event
99 \fn BMidiLocalConsumer::BMidiLocalConsumer(const char *name = NULL)
100 \brief Creates a new local consumer endpoint
102 The new endpoint is not visible to other applications until you Register() it.
104 You can tell the constructor what the name of the new consumer will be. If you
105 pass NULL (or use the default argument), then the consumer's name will be an
106 empty string. It won't be NULL, since endpoint names cannot be NULL.
108 There is no guarantee that the endpoint will be successfully created. For
109 example, the Midi Server may not be running. Therefore, you should always call
110 IsValid() after creating a new endpoint to make sure that everything went okay.
111 If not, Release() the object to reclaim memory and abort gracefully.
114 MyConsumer* cons = new MyConsumer(...);
115 if (!cons->IsValid())
118 ...exit gracefully...
126 \fn void BMidiLocalConsumer::SetLatency(bigtime_t latency)
127 \brief Changes the published latency of the consumer.
134 \fn int32 BMidiLocalConsumer::GetProducerID()
135 \brief Returns the ID of the producer that most recently sent a MIDI event to
138 You can call this from one of the hooks to determine which producer the event
144 \fn void BMidiLocalConsumer::SetTimeout(bigtime_t when, void* data)
145 \brief Requests that the Timeout() hook will be called at some point.
147 This method asks the consumer thread to call the Timeout() hook as soon as
148 possible after the timeout expires. For every call to SetTimeout(), the
149 Timeout() hook is only called once. Note: the term "timeout" may be a little
150 misleading; the hook will <I>always</I> be called, even if events are received
151 in the mean time. Apparently, this facility is handy for dealing with early
154 Note that the event thread blocks on the consumer's port as long as no events
155 arrive. By default no timeout is set, and as a result the thread blocks
156 forever. Your call to SetTimeout() doesn't change this. The new timeout value
157 will go into effect the next time the thread tries to read from the port, i.e.
158 after the first event has been received. If no event ever comes in, the
159 Timeout() hook will never be called. This also means that you cannot cancel a
160 timeout once you have set it. To repeat, calling SetTimeout() only takes effect
161 after at least one new event has been received.
163 \param when An absolute time that's measured against the system clock.
165 \param data A pointer to a "cookie" that you can pass along to Timeout(). The
166 data is not copied, so you must ensure that the pointer remains valid until
167 Timeout() is called. You typically delete the data inside Timeout().
172 \fn void BMidiLocalConsumer::Timeout(void* data)
173 \brief Hook function that is called per your own request.
179 \fn void BMidiLocalConsumer::Data(uchar* data, size_t length, bool atomic,
181 \brief Invoked when raw MIDI is received.
183 What the default implementation of Data() does depends on the value of atomic.
184 If atomic is true, the data received comprises a single MIDI event; i.e. one
185 status byte followed by the appropriate number of data bytes and nothing else.
186 In this case, Data() calls the event-specific hook function that corresponds to
187 that status byte. This optimization is used by the Midi Kit to allow faster
188 dispatch of events generated by the specific Spray functions from
191 If atomic is false, Data() ignores the MIDI event. If you want a consumer to
192 handle non-atomic events, you have to override Data() and program this
193 yourself. In that case, you probably also want to call the default
194 implementation to handle the "normal" MIDI events.
196 Data() is rarely overridden, but you can override it if you want to. If you do,
197 remember that the data buffer is owned by the Midi Kit. Do not attempt to
198 modify or free it, lest you wish to be laughed at by other developers.
200 \param data the MIDI event data
201 \param length byte size of the data buffer
202 \param atomic whether the data buffer contains a single complete MIDI event
203 \param time the requested performance time of the event
205 \sa BMidiLocalProducer::SprayData()
210 \fn void BMidiLocalConsumer::NoteOff(uchar channel, uchar note,
211 uchar velocity, bigtime_t time)
212 \brief Invoked when a Note Off event is received.
214 \sa BMidiLocalProducer::SprayNoteOff()
219 \fn void BMidiLocalConsumer::NoteOn(uchar channel, uchar note,
220 uchar velocity, bigtime_t time)
221 \brief Invoked when a Note On event is received.
223 \sa BMidiLocalProducer::SprayNoteOn()
228 \fn void BMidiLocalConsumer::KeyPressure(uchar channel, uchar note,
229 uchar pressure, bigtime_t time)
230 \brief Invoked when a Polyphonic Pressure (Aftertouch) event is received.
232 \sa BMidiLocalProducer::SprayKeyPressure()
237 \fn void BMidiLocalConsumer::ControlChange(uchar channel,
238 uchar controlNumber, uchar controlValue, bigtime_t time)
239 \brief Invoked when a Controller Change event is received.
241 \sa BMidiLocalProducer::SprayControlChange()
246 \fn void BMidiLocalConsumer::ProgramChange(uchar channel,
247 uchar programNumber, bigtime_t time)
248 \brief Invoked when a Program Change event is received.
250 \sa BMidiLocalProducer::SprayProgramChange()
255 \fn void BMidiLocalConsumer::ChannelPressure(uchar channel,
256 uchar pressure, bigtime_t time)
257 \brief Invoked when a Channel Pressure event is received.
259 \sa BMidiLocalProducer::SprayChannelPressure()
264 \fn void BMidiLocalConsumer::PitchBend(uchar channel, uchar lsb,
265 uchar msb, bigtime_t time)
266 \brief Invoked when a Pitch Bend event is received.
268 \sa BMidiLocalProducer::SprayPitchBend()
273 \fn void BMidiLocalConsumer::SystemExclusive(void* data, size_t length,
275 \brief Invoked when a System Exclusive event is received.
277 The data does not include the sysex start and end control bytes
278 (0xF0 and 0xF7), only the payload of the sysex message.
280 The data belongs to the Midi Kit and is only valid for the duration of
281 this event. You may not modify or free it.
283 \sa BMidiLocalProducer::SpraySystemExclusive()
288 \fn void BMidiLocalConsumer::SystemCommon(uchar status, uchar data1,
289 uchar data2, bigtime_t time)
290 \brief Invoked when a System Common event is received.
292 Not all data bytes are used for all common events. Unused bytes are
295 \sa BMidiLocalProducer::SpraySystemCommon()
300 \fn void BMidiLocalConsumer::SystemRealTime(uchar status, bigtime_t time)
301 \brief Invoked when a Real Time event is received.
303 \sa BMidiLocalProducer::SpraySystemRealTime()
308 \fn void BMidiLocalConsumer::TempoChange(int32 beatsPerMinute, bigtime_t time)
310 \brief Invoked when a Tempo Change event is received
311 \sa BMidiLocalProducer::SprayTempoChange()
316 \fn void BMidiLocalConsumer::AllNotesOff(bool justChannel, bigtime_t time)