explained Tempo Change event

explained AllNotesOff function


git-svn-id: file:///srv/svn/repos/haiku/trunk/current@2930 a95241bf-73f2-0310-859d-f6bbb57e9c96

docs/develop/midi/design.html

@@ -483,33 +483,27 @@ implementation, which all always strips the last byte even when it is not 0xF7.
 According to the MIDI spec, 0xF7 is not really required; any non-realtime 
 status byte ends a sysex message.</P></LI>
 
-<LI><P>SprayTempoChange() does nothing and TempoChange() is never called, just 
+<LI><P>SprayTempoChange() sends 0xFF5103tttttt, where tttttt is 60,000,000/bpm.
-like with the BeOS R5 Midi Kit. The Midi2Defs.h header defines the symbol 
+This feature is not really part of the MIDI spec, but an extension from the SMF
-B_TEMPO_CHANGE, which is equal to "general purpose controller 6". In theory, 
+(Standard MIDI File) format. Of course, the TempoChange() hook is called in
-SprayTempoChange() would send a Control Change event for the B_TEMPO_CHANGE 
+response to this message.</P></LI>
-controller, and TempoChange() would be invoked in response of such an event. 
-But the R5 Midi Kit doesn't do this, and neither do we.</P></LI>
 
 <LI><P>The MIDI spec allows for a number of shortcuts. A Note On event with 
-velocity 0 is to interpreted as a Note Off, for example. The Midi Kit does not 
+velocity 0 is supposed to be interpreted as a Note Off, for example. The Midi
-concern itself with these shortcuts. In this case, it still calls the NoteOn() 
+Kit does not concern itself with these shortcuts. In this case, it still calls
-hook with a velocity parameter of 0.</P></LI>
+the NoteOn() hook with a velocity parameter of 0.</P></LI>
 
 <LI><P>The purpose of BMidiLocalConsumer's AllNotesOff() function is not 
 entirely clear. All Notes Off is a so-called "channel mode message" and is 
-generated by doing a SprayControlChange(channel, B_ALL_NOTES_OFF, 0). One would 
+generated by doing a SprayControlChange(channel, B_ALL_NOTES_OFF, 0). BMidi has
-assume that the AllNotesOff() hook is called in response to the receipt of such 
+an AllNotesOff() function that sends an All Notes Off event to all channels,
-an event, but no, it is not. What's odd is that the documentation for the midi1 
+and possible Note Off events to all keys on all channels as well. I suspect
-kit's BMidi class does not describe this AllNotesOff() as a hook at all, but as 
+someone at Be was confused by AllNotesOff() being declared "virtual", and
-a spray function that sends an All Notes Off event to all 16 channels, and 
+thought it was a hook function. Only that would explain it being in
-optionally sends Note Off events for all notes too. Even stranger, BMidi's 
+BMidiLocalConsumer as opposed to BMidiLocalProducer, where it would have made
-AllNotesOff() is declared "virtual", just like all other hooks, and unlike any 
+sense. The disassembly for Be's libmidi2.so shows that AllNotesOff() is empty,
-of the other spray functions. Since AllNotesOff() is also part of 
+so to cut a long story short, our AllNotesOff() simply does nothing and is
-BMidiLocalConsumer, it really seems to be a hook function. The disassembly for 
+never invoked either.</P></LI>
-Be's libmidi2.so shows that AllNotesOff() is empty, which only supports this 
-hypothesis. Somebody at Be must have been very confused when they designed the 
-midi2 kit. To cut a long story short, AllNotesOff(), like TempoChange() does 
-nothing and is never invoked in our implementation.</P></LI>
 
 <LI><P>There are several types of System Common events, each of which takes a 
 different number of data bytes (0, 1, or 2). But SpraySystemCommon() and the