native_midi_mac.c

SDL_mixer 是一个基于 SDL 的混音器

	int			channel_pitch_bend[16];
	
	int			lastEventTime = 0;
	int			tempo = 500000;
	double		Ippqn = 1.0 / (1000*ppqn);
	double		tick = tempo * Ippqn;
	MIDIEvent	*eventPos = evntlist;
	MIDIEvent	*noteOffPos;
	Uint32 		*tunePos, *endPos;
	Uint32		*tuneSequence;
	size_t		tuneSize;
	
	/* allocate space for the tune header */
	tuneSize = 5000;
	tuneSequence = (Uint32 *)malloc(tuneSize * sizeof(Uint32));
	if (tuneSequence == NULL)
		return NULL;
	
	/* Set starting position in our tune memory */
	tunePos = tuneSequence;
	endPos = tuneSequence + tuneSize;

	/* Initialise the arrays */
	memset(part_poly,0,sizeof(part_poly));
	
	memset(channel_to_part,-1,sizeof(channel_to_part));
	memset(channel_pan,-1,sizeof(channel_pan));
	memset(channel_vol,-1,sizeof(channel_vol));
	memset(channel_pitch_bend,-1,sizeof(channel_pitch_bend));
	
	*numParts = 0;
	
	/*
	 * Now the major work - iterate over all GM events,
	 * and turn them into QuickTime Music format.
	 * At the same time, calculate the max. polyphony for each part,
	 * and also the part->instrument mapping.
	 */
	while(eventPos)
	{
		int status = (eventPos->status&0xF0)>>4;
		int channel = eventPos->status&0x0F;
		int part = channel_to_part[channel];
        int velocity, pitch;
        int value, controller;
        int bend;
        int newInst;
		
		/* Check if we are running low on space... */
		if((tunePos+16) > endPos)
		{
			/* Resize our data storage. */
			Uint32 		*oldTuneSequence = tuneSequence;

			tuneSize += BUFFER_INCREMENT;
			tuneSequence = (Uint32 *)realloc(tuneSequence, tuneSize * sizeof(Uint32));
			if(oldTuneSequence != tuneSequence)
				tunePos += tuneSequence - oldTuneSequence;
			endPos = tuneSequence + tuneSize;
		}
		
		switch (status)
		{
		case MIDI_STATUS_NOTE_OFF:
			assert(part>=0 && part<=31);

			/* Keep track of the polyphony of the current part */
			part_poly[part]--;
			break;
		case MIDI_STATUS_NOTE_ON:
			if (part < 0)
			{
				/* If no part is specified yet, we default to the first instrument, which
				   is piano (or the first drum kit if we are on the drum channel)
				*/
				int newInst;
				
				if (channel == 9)
					newInst = kFirstDrumkit + 1;		/* the first drum kit is the "no drum" kit! */
				else
					newInst = kFirstGMInstrument;
				part = channel_to_part[channel] = *numParts;
				part_to_inst[(*numParts)++] = newInst;
			}
			/* TODO - add support for more than 32 parts using eXtended QTMA events */
			assert(part<=31);
			
			/* Decode pitch & velocity */
			pitch = eventPos->data[0];
			velocity = eventPos->data[1];
			
			if (velocity == 0)
			{
				/* was a NOTE OFF in disguise, so we decrement the polyphony */
				part_poly[part]--;
			}
			else
			{
				/* Keep track of the polyphony of the current part */
				int foo = ++part_poly[part];
				if (part_poly_max[part] < foo)
					part_poly_max[part] = foo;

				/* Now scan forward to find the matching NOTE OFF event */
				for(noteOffPos = eventPos; noteOffPos; noteOffPos = noteOffPos->next)
				{
					if ((noteOffPos->status&0xF0)>>4 == MIDI_STATUS_NOTE_OFF
						&& channel == (eventPos->status&0x0F)
						&& pitch == noteOffPos->data[0])
						break;
					/* NOTE ON with velocity == 0 is the same as a NOTE OFF */
					if ((noteOffPos->status&0xF0)>>4 == MIDI_STATUS_NOTE_ON
						&& channel == (eventPos->status&0x0F)
						&& pitch == noteOffPos->data[0]
						&& 0 == noteOffPos->data[1])
						break;
				}
				
				/* Did we find a note off? Should always be the case, but who knows... */
				if (noteOffPos)
				{
					/* We found a NOTE OFF, now calculate the note duration */
					int duration = (int)((noteOffPos->time - eventPos->time)*tick);
					
					REST_IF_NECESSARY();
					/* Now we need to check if we get along with a normal Note Event, or if we need an extended one... */
					if (duration < 2048 && pitch>=32 && pitch<=95 && velocity>=0 && velocity<=127)
					{
						qtma_StuffNoteEvent(*tunePos, part, pitch, velocity, duration);
						tunePos++;
					}
					else
					{
						qtma_StuffXNoteEvent(*tunePos, *(tunePos+1), part, pitch, velocity, duration);
						tunePos+=2;
					}
				}
			}
			break;
		case MIDI_STATUS_AFTERTOUCH:
			/* NYI - use kControllerAfterTouch. But how are the parameters to be mapped? */
			break;
		case MIDI_STATUS_CONTROLLER:
			controller = eventPos->data[0];
			value = eventPos->data[1];

			switch(controller)
			{
			case 0:	/* bank change - igore for now */
				break;
			case kControllerVolume:
				if(channel_vol[channel] != value<<8)
				{
					channel_vol[channel] = value<<8;
					if(part>=0 && part<=31)
					{
						REST_IF_NECESSARY();
						qtma_StuffControlEvent(*tunePos, part, kControllerVolume, channel_vol[channel]);
						tunePos++;
					}
				}
				break;
			case kControllerPan:
				if(channel_pan[channel] != (value << 1) + 256)
				{
					channel_pan[channel] = (value << 1) + 256;
					if(part>=0 && part<=31)
					{
						REST_IF_NECESSARY();
						qtma_StuffControlEvent(*tunePos, part, kControllerPan, channel_pan[channel]);
						tunePos++;
					}
				}
				break;
			default:
				/* No other controllers implemented yet */;
				break;
			}
			
			break;
		case MIDI_STATUS_PROG_CHANGE:
			/* Instrument changed */
			newInst = eventPos->data[0];
			
			/* Channel 9 (the 10th channel) is different, it indicates a drum kit */
			if (channel == 9)
				newInst += kFirstDrumkit;
			else
				newInst += kFirstGMInstrument;
			/* Only if the instrument for this channel *really* changed, add a new part. */
			if(newInst != part_to_inst[part])
			{
				/* TODO maybe make use of kGeneralEventPartChange here,
				   to help QT reuse note channels?
				*/
				part = channel_to_part[channel] = *numParts;
				part_to_inst[(*numParts)++] = newInst;

				if(channel_vol[channel] >= 0)
				{
					REST_IF_NECESSARY();
					qtma_StuffControlEvent(*tunePos, part, kControllerVolume, channel_vol[channel]);
					tunePos++;
				}
				if(channel_pan[channel] >= 0)
				{
					REST_IF_NECESSARY();
					qtma_StuffControlEvent(*tunePos, part, kControllerPan, channel_pan[channel]);
					tunePos++;
				}
				if(channel_pitch_bend[channel] >= 0)
				{
					REST_IF_NECESSARY();
					qtma_StuffControlEvent(*tunePos, part, kControllerPitchBend, channel_pitch_bend[channel]);
					tunePos++;
				}			
			}
			break;
		case MIDI_STATUS_PRESSURE:
			/* NYI */
			break;
		case MIDI_STATUS_PITCH_WHEEL:
			/* In the midi spec, 0x2000 = center, 0x0000 = - 2 semitones, 0x3FFF = +2 semitones
			   but for QTMA, we specify it as a 8.8 fixed point of semitones
			   TODO: detect "pitch bend range changes" & honor them!
			*/
			bend = (eventPos->data[0] & 0x7f) | ((eventPos->data[1] & 0x7f) << 7);
			
			/* "Center" the bend */
			bend -= 0x2000;
			
			/* Move it to our format: */
			bend <<= 4;
			
			/* If it turns out the pitch bend didn't change, stop here */
			if(channel_pitch_bend[channel] == bend)
				break;
			
			channel_pitch_bend[channel] = bend;
			if(part>=0 && part<=31)
			{
				/* Stuff a control event */
				REST_IF_NECESSARY();
				qtma_StuffControlEvent(*tunePos, part, kControllerPitchBend, bend);
				tunePos++;
			}			
			break;
		case MIDI_STATUS_SYSEX:
			if (eventPos->status == 0xFF && eventPos->data[0] == 0x51) /* Tempo change */
			{
				tempo = (eventPos->extraData[0] << 16) +
					(eventPos->extraData[1] << 8) +
					eventPos->extraData[2];
				
				tick = tempo * Ippqn;
			}
			break;
		}
		
		/* on to the next event */
		eventPos = eventPos->next;
	} 
	
	/* Finally, place an end marker */
	*tunePos = kEndMarkerValue;
	
	return tuneSequence;
}

Uint32 *BuildTuneHeader(int part_poly_max[32], int part_to_inst[32], int numParts)
{
	Uint32			*myHeader;
	Uint32			*myPos1, *myPos2;		/* pointers to the head and tail long words of a music event */
	NoteRequest		*myNoteRequest;
	NoteAllocator	myNoteAllocator;		/* for the NAStuffToneDescription call */
	ComponentResult	myErr = noErr;
	int				part;

	myHeader = NULL;
	myNoteAllocator = NULL;

	/*
	 * Open up the Note Allocator
	 */
	myNoteAllocator = OpenDefaultComponent(kNoteAllocatorComponentType,0);
	if (myNoteAllocator == NULL)
		goto bail;
	
	/*
	 * Allocate space for the tune header
	 */
	myHeader = (Uint32 *)
			NewPtrClear((numParts * kNoteRequestEventLength + kMarkerEventLength) * sizeof(Uint32));
	if (myHeader == NULL)
		goto bail;
	
	myPos1 = myHeader;
	
	/*
	 * Loop over all parts
	 */
	for(part = 0; part < numParts; ++part)
	{
		/*
		 * Stuff request for the instrument with the given polyphony
		 */
		myPos2 = myPos1 + (kNoteRequestEventLength - 1); /* last longword of general event */
		qtma_StuffGeneralEvent(*myPos1, *myPos2, part, kGeneralEventNoteRequest, kNoteRequestEventLength);
		myNoteRequest = (NoteRequest *)(myPos1 + 1);
		myNoteRequest->info.flags = 0;
		/* I'm told by the Apple people that the Quicktime types were poorly designed and it was 
		 * too late to change them. On little endian, the BigEndian(Short|Fixed) types are structs
		 * while on big endian they are primitive types. Furthermore, Quicktime failed to 
		 * provide setter and getter functions. To get this to work, we need to case the 
		 * code for the two possible situations.
		 * My assumption is that the right-side value was always expected to be BigEndian
		 * as it was written way before the Universal Binary transition. So in the little endian
		 * case, OSSwap is used.
		 */
#if SDL_BYTEORDER == SDL_LIL_ENDIAN
		myNoteRequest->info.polyphony.bigEndianValue = OSSwapHostToBigInt16(part_poly_max[part]);
		myNoteRequest->info.typicalPolyphony.bigEndianValue = OSSwapHostToBigInt32(0x00010000);
#else
		myNoteRequest->info.polyphony = part_poly_max[part];
		myNoteRequest->info.typicalPolyphony = 0x00010000;
#endif
		myErr = NAStuffToneDescription(myNoteAllocator,part_to_inst[part],&myNoteRequest->tone);
		if (myErr != noErr)
			goto bail;
		
		/* move pointer to beginning of next event */
		myPos1 += kNoteRequestEventLength;
	}

	*myPos1 = kEndMarkerValue;		/* end of sequence marker */


bail:
	if(myNoteAllocator)
		CloseComponent(myNoteAllocator);

	/* if we encountered an error, dispose of the storage we allocated and return NULL */
	if (myErr != noErr) {
		DisposePtr((Ptr)myHeader);
		myHeader = NULL;
	}

	return myHeader;
}

#endif /* MacOS native MIDI support */