Delphi: How to send MIDI to a hosted VST plugin?

I want to use VST plugins in my Delphi program which acts as a VST host. I have tried the tobybear examples, used the delphiasiovst stuf, got some of it even working, but... I don't know how to send MIDI messages to the plugin (I am aware that most plugins will not handle MIDI, but I have an example plugin that does).

To be more specific: I expect that when I send a MIDI message, I have to either use one or other method in the VST plugin or reroute the MIDI output. I just don't know how.

Can anyone point me to documentation or code on how to do this? Thanks in advance.

Arnold

I use two test plugins: the one compiled from the DelphiAsioVst package and PolyIblit. Both work in Finale and LMMS. Loaded into my test program both show their VST editor.

I did insert the TvstEvent record and initialized it, I inserted the MIDIData and the AddMIDIData procedures and a timer to provide test data and to execute the ProcessEvents routine of the plugin. ProcessEvents gets the correct test data, but no sound is heard. I hear something when I send it directly to the midi output port.

In the code below the PropcessEvents should be sufficient imho, the additional code is a test whether the MIDI information is correctly sent. VstHost [0] is the first plugin, being either the PolyIblit or the VSTPlugin, depending on the test.

procedure TMain_VST_Demo.TimerTimer (Sender: TObject);
var i: Int32;
begin
//   MIDIOutput.PutShort ($90, 60, 127);
   MIDIData (0, $90, 60, 127);

   if FMDataCnt > 0 then
   begin
      FMyEvents.numEvents := FMDataCnt;
      VSTHost[0].ProcessEvents(@FMyEvents);
//    if (FCurrentMIDIOut > 0) and MIMidiThru.Checked then
//     begin
      for i := 0 to FMDataCnt - 1 do
      MIDIOutput.PutShort (PVstMidiEvent (FMyEvents.events[i])^.midiData[0],
                           PVstMidiEvent (FMyEvents.events[i])^.midiData[1],
                           PVstMidiEvent (FMyEvents.events[i])^.midiData[2]);
//       FMidiOutput.Send(//FCurrentMIDIOut - 1,
//                   PVstMidiEvent(FMyEvents.events[i])^.midiData[0],
//                   PVstMidiEvent(FMyEvents.events[i])^.midiData[1],
//                   PVstMidiEvent(FMyEvents.events[i])^.midiData[2]);
//     end;
     FMDataCnt := 0;
   end;
end; // TimerTimer //

So I don't get the events in the plugin. Any idea what do I wrong?

Solution

You should really look at the minihost core example (Delphi ASIO project, v1.4).

There is a use of midi events. Basically

you have a TVstEvents variable ( let's say MyMidiEvents: TvstEvents).
for the whole runtime you allocate the memory for this variable ( in the app constructor for exmaple)
When you have an event in your MIDI callback, you copy it on the TVstEvents stack.
Before calling process in the TVstHost, you call MyVstHost.ProcessEvents( @MyMidiEvents ).

this is how it's done in the example (minihost core), for each previously steps:

1/ at line 215, declaration

FMyEvents: TVstEvents;

2/ at line 376, allocation:

for i := 0 to 2047 do
begin
 GetMem(FMyEvents.Events[i], SizeOf(TVSTMidiEvent));
 FillChar(FMyEvents.Events[i]^, SizeOf(TVSTMidiEvent), 0);
 with PVstMidiEvent(FMyEvents.Events[i])^ do
  begin
   EventType := etMidi;
   ByteSize := 24;
  end;
end;

3/ at line 986 then at line 1782, the midi event is copied from the callback:

the callback

procedure TFmMiniHost.MidiData(const aDeviceIndex: Integer; const aStatus, aData1, aData2: Byte);
begin
 if aStatus = $FE then exit; // ignore active sensing
 if (not Player.CbOnlyChannel1.Checked) or ((aStatus and $0F) = 0) then
  begin
   if (aStatus and $F0) = $90
    then NoteOn(aStatus, aData1, aData2) //ok
    else
   if (aStatus and $F0) = $80
    then NoteOff(aStatus, aData1)
    else AddMidiData(aStatus, aData1, aData2);
  end;
end;

event copy

procedure TFmMiniHost.AddMIDIData(d1, d2, d3: byte; pos: Integer = 0);
begin
 FDataSection.Acquire; 
 try
  if FMDataCnt > 2046 
   then exit;                 

  inc(FMDataCnt);
  with PVstMidiEvent(FMyEvents.events[FMDataCnt - 1])^ do
   begin
    EventType := etMidi;
    deltaFrames := pos;
    midiData[0] := d1;
    midiData[1] := d2;
    midiData[2] := d3;
   end;
 finally 
  FDataSection.Release;
 end; 
end;

4/ at line 2322, in TAsioHost.Bufferswitch, the TVstHost.ProcessEvents is called

FDataSection.Acquire;
try
  if FMDataCnt > 0 then
   begin
    FMyEvents.numEvents := FMDataCnt;

    VSTHost[0].ProcessEvents(FMyEvents);

    if (FCurrentMIDIOut > 0) and MIMidiThru.Checked then
     begin
      for i := 0 to FMDataCnt - 1 do
       FMidiOutput.Send(FCurrentMIDIOut - 1,
                   PVstMidiEvent(FMyEvents.events[i])^.midiData[0],
                   PVstMidiEvent(FMyEvents.events[i])^.midiData[1],
                   PVstMidiEvent(FMyEvents.events[i])^.midiData[2]);
     end;
     FMDataCnt := 0;
   end;
 finally  
  FDataSection.Release;
 end;

this should help you a lot if you were not able to analyse the method used.