native_midi/native_midi_common.c

/*
  native_midi:  Hardware Midi support for the SDL_mixer library
  Copyright (C) 2000,2001  Florian 'Proff' Schulze <florian.proff.schulze@gmx.net>

  This software is provided 'as-is', without any express or implied
  warranty.  In no event will the authors be held liable for any damages
  arising from the use of this software.

  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it
  freely, subject to the following restrictions:

  1. The origin of this software must not be misrepresented; you must not
     claim that you wrote the original software. If you use this software
     in a product, an acknowledgment in the product documentation would be
     appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be
     misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.
*/


#include "native_midi_common.h"

#include "../SDL_mixer.h"

#include <stdlib.h>
#include <string.h>
#include <limits.h>

/* The constant 'MThd' */
#define MIDI_MAGIC	0x4d546864

/* A single midi track as read from the midi file */
typedef struct
{
    Uint8 *data;                    /* MIDI message stream */
    int len;                        /* length of the track data */
} MIDITrack;

/* A midi file, stripped down to the absolute minimum - divison & track data */
typedef struct
{
    int division;                   /* number of pulses per quarter note (ppqn) */
    int nTracks;                    /* number of tracks */
    MIDITrack *track;               /* tracks */
} MIDIFile;


/* Some macros that help us stay endianess-independant */
#if SDL_BYTEORDER == SDL_BIG_ENDIAN
#define BE_SHORT(x) (x)
#define BE_LONG(x) (x)
#else
#define BE_SHORT(x) ((((x)&0xFF)<<8) | (((x)>>8)&0xFF))
#define BE_LONG(x)  ((((x)&0x0000FF)<<24) | \
             (((x)&0x00FF00)<<8) | \
             (((x)&0xFF0000)>>8) | \
             (((x)>>24)&0xFF))
#endif


/* Get Variable Length Quantity */
static int GetVLQ(MIDITrack *track, int *currentPos)
{
    int l = 0;
    Uint8 c;
    while(1)
    {
        c = track->data[*currentPos];
        (*currentPos)++;
        l += (c & 0x7f);
        if (!(c & 0x80))
            return l;
        l <<= 7;
    }
}

/* Create a single MIDIEvent */
static MIDIEvent *CreateEvent(Uint32 time, Uint8 event, Uint8 a, Uint8 b)
{
    MIDIEvent *newEvent;

    newEvent = calloc(1, sizeof(MIDIEvent));

    if (newEvent)
    {
        newEvent->time = time;
        newEvent->status = event;
        newEvent->data[0] = a;
        newEvent->data[1] = b;
    }
    else
        Mix_SetError("Out of memory");

    return newEvent;
}

/* Convert a single midi track to a list of MIDIEvents */
static MIDIEvent *MIDITracktoStream(MIDITrack *track)
{
    Uint32 atime = 0;
    Uint32 len = 0;
    Uint8 event,type,a,b;
    Uint8 laststatus = 0;
    Uint8 lastchan = 0;
    int currentPos = 0;
    int end = 0;
    MIDIEvent *head = CreateEvent(0,0,0,0); /* dummy event to make handling the list easier */
    MIDIEvent *currentEvent = head;

    while (!end)
    {
        if (currentPos >= track->len)
            break; /* End of data stream reached */

        atime += GetVLQ(track, &currentPos);
        event = track->data[currentPos++];

        /* Handle SysEx seperatly */
        if (((event>>4) & 0x0F) == MIDI_STATUS_SYSEX)
        {
            if (event == 0xFF)
            {
                type = track->data[currentPos];
                currentPos++;
                switch(type)
                {
                    case 0x2f: /* End of data marker */
                        end = 1;
                    case 0x51: /* Tempo change */
                        /*
                        a=track->data[currentPos];
                        b=track->data[currentPos+1];
                        c=track->data[currentPos+2];
                        AddEvent(song, atime, MEVT_TEMPO, c, b, a);
                        */
                        break;
                }
            }
            else
                type = 0;

            len = GetVLQ(track, &currentPos);

            /* Create an event and attach the extra data, if any */
            currentEvent->next = CreateEvent(atime, event, type, 0);
            currentEvent = currentEvent->next;
            if (NULL == currentEvent)
            {
                FreeMIDIEventList(head);
                return NULL;
            }
            if (len)
            {
                currentEvent->extraLen = len;
                currentEvent->extraData = malloc(len);
                memcpy(currentEvent->extraData, &(track->data[currentPos]), len);
                currentPos += len;
            }
        }
        else
        {
            a = event;
            if (a & 0x80) /* It's a status byte */
            {
                /* Extract channel and status information */
                lastchan = a & 0x0F;
                laststatus = (a>>4) & 0x0F;

                /* Read the next byte which should always be a data byte */
                a = track->data[currentPos++] & 0x7F;
            }
            switch(laststatus)
            {
                case MIDI_STATUS_NOTE_OFF:
                case MIDI_STATUS_NOTE_ON: /* Note on */
                case MIDI_STATUS_AFTERTOUCH: /* Key Pressure */
                case MIDI_STATUS_CONTROLLER: /* Control change */
                case MIDI_STATUS_PITCH_WHEEL: /* Pitch wheel */
                    b = track->data[currentPos++] & 0x7F;
                    currentEvent->next = CreateEvent(atime, (Uint8)((laststatus<<4)+lastchan), a, b);
                    currentEvent = currentEvent->next;
                    if (NULL == currentEvent)
                    {
                        FreeMIDIEventList(head);
                        return NULL;
                    }
                    break;

                case MIDI_STATUS_PROG_CHANGE: /* Program change */
                case MIDI_STATUS_PRESSURE: /* Channel pressure */
                    a &= 0x7f;
                    currentEvent->next = CreateEvent(atime, (Uint8)((laststatus<<4)+lastchan), a, 0);
                    currentEvent = currentEvent->next;
                    if (NULL == currentEvent)
                    {
                        FreeMIDIEventList(head);
                        return NULL;
                    }
                    break;

                default: /* Sysex already handled above */
                    break;
            }
        }
    }

    currentEvent = head->next;
    free(head); /* release the dummy head event */
    return currentEvent;
}

/*
 *  Convert a midi song, consisting of up to 32 tracks, to a list of MIDIEvents.
 *  To do so, first convert the tracks seperatly, then interweave the resulting
 *  MIDIEvent-Lists to one big list.
 */
static MIDIEvent *MIDItoStream(MIDIFile *mididata)
{
    MIDIEvent **track;
    MIDIEvent *head = CreateEvent(0,0,0,0); /* dummy event to make handling the list easier */
    MIDIEvent *currentEvent = head;
    int trackID;

    if (NULL == head)
        return NULL;

    track = (MIDIEvent**) calloc(1, sizeof(MIDIEvent*) * mididata->nTracks);
    if (NULL == track)
    {
        free(head);
        return NULL;
    }

    /* First, convert all tracks to MIDIEvent lists */
    for (trackID = 0; trackID < mididata->nTracks; trackID++)
        track[trackID] = MIDITracktoStream(&mididata->track[trackID]);

    /* Now, merge the lists. */
    /* TODO */
    while(1)
    {
        Uint32 lowestTime = INT_MAX;
        int currentTrackID = -1;

        /* Find the next event */
        for (trackID = 0; trackID < mididata->nTracks; trackID++)
        {
            if (track[trackID] && (track[trackID]->time < lowestTime))
            {
                currentTrackID = trackID;
                lowestTime = track[currentTrackID]->time;
            }
        }

        /* Check if we processes all events */
        if (currentTrackID == -1)
            break;

        currentEvent->next = track[currentTrackID];
        track[currentTrackID] = track[currentTrackID]->next;

        currentEvent = currentEvent->next;


        lowestTime = 0;
    }

    /* Make sure the list is properly terminated */
    currentEvent->next = 0;

    currentEvent = head->next;
    free(track);
    free(head); /* release the dummy head event */
    return currentEvent;
}

static int ReadMIDIFile(MIDIFile *mididata, SDL_RWops *src)
{
    int i = 0;
    Uint32  ID;
    Uint32  size;
    Uint16  format;
    Uint16  tracks;
    Uint16  division;

    if (!mididata)
        return 0;
    if (!src)
        return 0;

    /* Make sure this is really a MIDI file */
    SDL_RWread(src, &ID, 1, 4);
    if (BE_LONG(ID) != MIDI_MAGIC)
        return 0;

    /* Header size must be 6 */
    SDL_RWread(src, &size, 1, 4);
    size = BE_LONG(size);
    if (size != 6)
        return 0;

    /* We only support format 0 and 1, but not 2 */
    SDL_RWread(src, &format, 1, 2);
    format = BE_SHORT(format);
    if (format != 0 && format != 1)
        return 0;

    SDL_RWread(src, &tracks, 1, 2);
    tracks = BE_SHORT(tracks);
    mididata->nTracks = tracks;

    /* Allocate tracks */
    mididata->track = (MIDITrack*) calloc(1, sizeof(MIDITrack) * mididata->nTracks);
    if (NULL == mididata->track)
    {
        Mix_SetError("Out of memory");
        goto bail;
    }

    /* Retrieve the PPQN value, needed for playback */
    SDL_RWread(src, &division, 1, 2);
    mididata->division = BE_SHORT(division);


    for (i=0; i<tracks; i++)
    {
        SDL_RWread(src, &ID, 1, 4);  /* We might want to verify this is MTrk... */
        SDL_RWread(src, &size, 1, 4);
        size = BE_LONG(size);
        mididata->track[i].len = size;
        mididata->track[i].data = malloc(size);
        if (NULL == mididata->track[i].data)
        {
            Mix_SetError("Out of memory");
            goto bail;
        }
        SDL_RWread(src, mididata->track[i].data, 1, size);
    }
    return 1;

bail:
    for(;i >= 0; i--)
    {
        if (mididata->track[i].data)
            free(mididata->track[i].data);
    }

    return 0;
}

MIDIEvent *CreateMIDIEventList(SDL_RWops *src, Uint16 *division)
{
    MIDIFile *mididata = NULL;
    MIDIEvent *eventList;
    int trackID;

    mididata = calloc(1, sizeof(MIDIFile));
    if (!mididata)
        return NULL;

    /* Open the file */
    if ( src != NULL )
    {
        /* Read in the data */
        if ( ! ReadMIDIFile(mididata, src))
        {
            free(mididata);
            return NULL;
        }
    }
    else
    {
        free(mididata);
        return NULL;
    }

    if (division)
        *division = mididata->division;

    eventList = MIDItoStream(mididata);
    if (eventList == NULL)
    {
        free(mididata);
        return NULL;
    }
    for(trackID = 0; trackID < mididata->nTracks; trackID++)
    {
        if (mididata->track[trackID].data)
            free(mididata->track[trackID].data);
    }
    free(mididata->track);
    free(mididata);

    return eventList;
}

void FreeMIDIEventList(MIDIEvent *head)
{
    MIDIEvent *cur, *next;

    cur = head;

    while (cur)
    {
        next = cur->next;
        if (cur->extraData)
            free (cur->extraData);
        free (cur);
        cur = next;
    }
}