Re: [Denemo-devel] What is the duration of a measure

[Jeremiah Benham]

On Tue, 2009-09-22 at 09:07 +0100, Richard Shann wrote:
> Jeremiah
> Do you know if we have a function to get the duration of a whole measure
> given the time signature?
> I am trying to improve the whole measure rest thing, I can do that if I
> can transform
>       4/4         -->   r1
>       12/8        -->   r1.

I started witting something like that in importmidi.c  In midi there is
a value called ppqn. This stands for Pulses Per Quarter Note. Usually
this value is set to 384. To find out how many pulses are in a measure
you do this:

gint barlength = ppqn * 4 * numerator / denominator;

numerator and denominator refer to the time signature.

Then in importmidi.c line 776. There is this:

while(mididata->barlength - mididata->bartime){
        rest = mididata->barlength - mididata->bartime;
        struct notetype length = ConvertLength(rest, mididata);
        new_dnm_object(mididata, mididata->currentnote, length, FALSE);
        mididata->bartime += ConvertNoteType2ticks(mididata, &length);
        mididata->lastoff += ConvertNoteType2ticks(mididata, &length);
      }

and lines 786-791:


if (rest){
        struct notetype length = ConvertLength(rest, mididata);
        new_dnm_object(mididata, mididata->currentnote, length, FALSE);
        mididata->bartime = mididata->bartime +
ConvertNoteType2ticks(mididata, &length);
        mididata->lastoff += ConvertNoteType2ticks(mididata, &length);
        rest = 0;


So now you need the function ConvertLength:

notetype ConvertLength(gint duration, midicallback *mididata){
 /*convert length to 2 = quarter, 1 = half, 0 = whole etc...... */
        /* quarter = 384, half = 768, whole = 1536*/
  notetype gnotetype;
  gint PPQN = mididata->smf->ppqn;
  gint notetype = 0;
  gint numofdots = 0;
  gint tied = 0;
  gint leftover = 0;
  gint dsq = (4 * PPQN);


  while ((dsq >> notetype) > duration)
          notetype++;

  leftover = duration - (dsq >> notetype);

  while (leftover >= (dsq >> (notetype +1))){
        leftover -= (dsq >> (notetype +1));
        numofdots++;
  }

  gnotetype.notetype =
notetype;                                          
  gnotetype.numofdots = numofdots;
  gnotetype.tied = leftover;
  return gnotetype;
}


ConvertLength converts ticks to a notetype. I also have this function if
you need to go the other way around:

ConvertNoteType2ticks(midicallback *mididata, notetype *gnotetype){
  gint ticks;
  gint PPQN = mididata->smf->ppqn;
  gint notetype = (int) gnotetype->notetype;
  gint numofdots = (int) gnotetype->numofdots;
  gint dsq = (4 * PPQN);
  gint i = 0;

  ticks = dsq >> notetype;
  while (i++ < numofdots)
    ticks += dsq >> notetype + 1;

  return ticks;
}


IHTH,
Jeremiah


> and so on
> (hmm, for all possible keysigs? it would mean 
> 
> 5/8 --> r2 r8
> 
> or anything equivalent but I don't personally need this)
> 
> My question is about Denemo internals really - is there some conversion
> from keysignature to whole measure length that you have come across
> doing the stuff you have done so far?
> Richard
> 
> 
> 
> 
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