midi_tracks()

[jarnoh]

I have no idea what the method does, or why it is written like that. Copy paste errors or is it using some awesome drum syncing?

[JayFoxRox]

(Just to clarify: I did not write the original code; I just thought it would be fun to document it)

---

It's a bit ugly, but otherwise makes sense; here's the code for reference:

doomsday/demo.cpp

Lines 52 to 57 in 571f553

	if(*midi_tech04!=-1)
	{
	while(*midi_tech04!=-1 && *midi_tech04/960.f<=t) midi_tech04+=3;
	tech04_keytime[midi_tech04[-2]]=midi_tech04[-3]/960.f;
	tech04_keyvelocity[midi_tech04[-2]]=midi_tech04[-1]/127.f;
	}

---

midi_tech04 points into a list of MIDI events (track_tech04), the structure of each MIDI event appears to be like this (with negative indices referring to the previous event):

// All fields will be -1 for the last event, to signal end of track
struct {
  int time;     // access using [0] or [-3]
  int key;      // access using [1] or [-2]
  int velocity; // access using [2] or [-1]
};

// Equivalent to `midi_tech04[0]` or `midi_tech04.time` (also used in next step)
// Checks if playback has finished (timestamp will be -1)
if(*midi_tech04!=-1)
{
    // Search for the next event by repeatedly skipping events (advance pointer 3 fields = 1 event)
    // Done while the current timestamp is reached (`/960.f<=t`, where `960.f` is timescale) and end isn't reached (`!=-1`).
    while(*midi_tech04!=-1 && *midi_tech04/960.f<=t) midi_tech04+=3;

    // Note: Pseudocode differs below:
    //       `midi_tech04` named fields should access at previous event (`midi_tech04-3`).

    // Equivalent to `tech04_keytime[midi_tech04.key]=midi_tech04.time/960.f;`
    // (where `/960.0f` is timescale)
    tech04_keytime[midi_tech04[-2]]=midi_tech04[-3]/960.f;

    // Equivalent to `tech04_keyvelocity[midi_tech04.key]=midi_tech04.velocity/127.f;`
    // (where `/127.f` is volume control)
    tech04_keyvelocity[midi_tech04[-2]]=midi_tech04[-1]/127.f;
}

The same code pattern repeats for each MIDI track.
So, for each track, it just advances to the next MIDI event and punches the key for that event.

The issue with it that I'm seeing is that it only plays one key for each track at a time.
So if midi_tracks() isn't called often enough (= t advances so much that more than 1 key would play) it will skip keys.
The loop from line 54 should also contain line 55 and 56 (punching keys) to address this.

Probably written like this to keep the music exporter simple + lazyness.