55 lines
2.3 KiB
Plaintext
55 lines
2.3 KiB
Plaintext
/*!
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\class BMidiConsumer MidiConsumer.h
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\brief Receives MIDI events from a producer
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A consumer is an object that knows how to deal with incoming MIDI events. A
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consumer can be connected to multiple producers at the same time. There is no
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way to find out which producers are connected to this consumer just by looking
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at the BMidiConsumer object; you will have to consult BMidiRoster for that.
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A BMidiConsumer either represents a local consumer, i.e. a class extending from
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BMidiLocalConsumer, or is a proxy for a remote object published by another app.
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*/
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/*!
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\fn bigtime_t BMidiConsumer::Latency() const
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\brief Returns the latency of this consumer
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The latency is measured in microseconds. Producers should attempt to get MIDI
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events to this consumer by <I>(when - latency)</I>. You do this by subtracting
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the latency from the performance time when you spray the events (provided that
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you spray these events ahead of time, of course).
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You cannot <I>set</I> the latency on a BMidiConsumer, only on a
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BMidiLocalConsumer.
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The latency issue gets slightly more complicated when multiple endpoints are
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chained together, as in the following picture:
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\verbatim
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+-------+ +-------------+ +-------+
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| | | | | |
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| prodA |---->| consB prodB |---->| consC |
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| | | | | |
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+-------+ +-------------+ +-------+
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appA appB (filter) appC
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\endverbatim
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Suppose consC has 200ms latency, and consB has 100ms latency. If consB simply
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reports 100ms, then prodA will schedule its events for (t - 100), which is
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really 200ms too late. (Of course, producers send out their events as soon as
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possible, so depending on the load of the system, everything may work out just
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fine.)
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ConsB should report the latency of the consumer that is hooked up to its
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output, consC, in addition to its own latency. In other words, the full
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downstream latency. So, the reported latency in this case would be 300ms. This
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also means that appB should change the latency of consB when prodB makes or
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breaks a connection, and when consC reports a latency change. (If multiple
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consumers are connected to prodB, you should take the slowest one.)
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Unfortunately, the Midi Kit provides no easy mechanism for doing any of this,
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so you are on your own here.
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*/
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