three.js/examples/js/loaders/lwo/IFFParser.js

( function () {

	/**
 * === IFFParser ===
 * - Parses data from the IFF buffer.
 * - LWO3 files are in IFF format and can contain the following data types, referred to by shorthand codes
 *
 * ATOMIC DATA TYPES
 *  ID Tag - 4x 7 bit uppercase ASCII chars: ID4
 *  signed integer, 1, 2, or 4 byte length: I1, I2, I4
 *  unsigned integer, 1, 2, or 4 byte length: U1, U2, U4
 *  float, 4 byte length: F4
 *  string, series of ASCII chars followed by null byte (If the length of the string including the null terminating byte is odd, an extra null is added so that the data that follows will begin on an even byte boundary): S0
 *
 * COMPOUND DATA TYPES
 *  Variable-length Index (index into an array or collection): U2 or U4 : VX
 *  Color (RGB): F4 + F4 + F4: COL12
 *  Coordinate (x, y, z): F4 + F4 + F4: VEC12
 *  Percentage F4 data type from 0->1 with 1 = 100%: FP4
 *  Angle in radian F4: ANG4
 *  Filename (string) S0: FNAM0
 *  XValue F4 + index (VX) + optional envelope( ENVL ): XVAL
 *  XValue vector VEC12 + index (VX) + optional envelope( ENVL ): XVAL3
 *
 *  The IFF file is arranged in chunks:
 *  CHUNK = ID4 + length (U4) + length X bytes of data + optional 0 pad byte
 *  optional 0 pad byte is there to ensure chunk ends on even boundary, not counted in size
 *
 * COMPOUND DATA TYPES
 * - Chunks are combined in Forms (collections of chunks)
 * - FORM = string 'FORM' (ID4) + length (U4) + type (ID4) + optional ( CHUNK | FORM )
 * - CHUNKS and FORMS are collectively referred to as blocks
 * - The entire file is contained in one top level FORM
 *
 **/
	function IFFParser() {

		this.debugger = new Debugger();
		// this.debugger.enable(); // un-comment to log IFF hierarchy.

	}

	IFFParser.prototype = {
		constructor: IFFParser,
		parse: function ( buffer ) {

			this.reader = new DataViewReader( buffer );
			this.tree = {
				materials: {},
				layers: [],
				tags: [],
				textures: []
			};

			// start out at the top level to add any data before first layer is encountered
			this.currentLayer = this.tree;
			this.currentForm = this.tree;
			this.parseTopForm();
			if ( this.tree.format === undefined ) return;
			if ( this.tree.format === 'LWO2' ) {

				this.parser = new THREE.LWO2Parser( this );
				while ( ! this.reader.endOfFile() ) this.parser.parseBlock();

			} else if ( this.tree.format === 'LWO3' ) {

				this.parser = new THREE.LWO3Parser( this );
				while ( ! this.reader.endOfFile() ) this.parser.parseBlock();

			}

			this.debugger.offset = this.reader.offset;
			this.debugger.closeForms();
			return this.tree;

		},
		parseTopForm() {

			this.debugger.offset = this.reader.offset;
			var topForm = this.reader.getIDTag();
			if ( topForm !== 'FORM' ) {

				console.warn( 'LWOLoader: Top-level FORM missing.' );
				return;

			}

			var length = this.reader.getUint32();
			this.debugger.dataOffset = this.reader.offset;
			this.debugger.length = length;
			var type = this.reader.getIDTag();
			if ( type === 'LWO2' ) {

				this.tree.format = type;

			} else if ( type === 'LWO3' ) {

				this.tree.format = type;

			}

			this.debugger.node = 0;
			this.debugger.nodeID = type;
			this.debugger.log();
			return;

		},
		///
		// FORM PARSING METHODS
		///

		// Forms are organisational and can contain any number of sub chunks and sub forms
		// FORM ::= 'FORM'[ID4], length[U4], type[ID4], ( chunk[CHUNK] | form[FORM] ) * }
		parseForm( length ) {

			var type = this.reader.getIDTag();
			switch ( type ) {

				// SKIPPED FORMS
				// if skipForm( length ) is called, the entire form and any sub forms and chunks are skipped

				case 'ISEQ': // Image sequence
				case 'ANIM': // plug in animation
				case 'STCC': // Color-cycling Still
				case 'VPVL':
				case 'VPRM':
				case 'NROT':
				case 'WRPW': // image wrap w ( for cylindrical and spherical projections)
				case 'WRPH': // image wrap h
				case 'FUNC':
				case 'FALL':
				case 'OPAC':
				case 'GRAD': // gradient texture
				case 'ENVS':
				case 'VMOP':
				case 'VMBG':

					// Car Material FORMS
				case 'OMAX':
				case 'STEX':
				case 'CKBG':
				case 'CKEY':
				case 'VMLA':
				case 'VMLB':
					this.debugger.skipped = true;
					this.skipForm( length ); // not currently supported
					break;

					// if break; is called directly, the position in the lwoTree is not created
					// any sub chunks and forms are added to the parent form instead
				case 'META':
				case 'NNDS':
				case 'NODS':
				case 'NDTA':
				case 'ADAT':
				case 'AOVS':
				case 'BLOK':

					// used by texture nodes
				case 'IBGC': // imageBackgroundColor
				case 'IOPC': // imageOpacity
				case 'IIMG': // hold reference to image path
				case 'TXTR':
					// this.setupForm( type, length );
					this.debugger.length = 4;
					this.debugger.skipped = true;
					break;
				case 'IFAL': // imageFallof
				case 'ISCL': // imageScale
				case 'IPOS': // imagePosition
				case 'IROT': // imageRotation
				case 'IBMP':
				case 'IUTD':
				case 'IVTD':
					this.parseTextureNodeAttribute( type );
					break;
				case 'ENVL':
					this.parseEnvelope( length );
					break;

					// CLIP FORM AND SUB FORMS

				case 'CLIP':
					if ( this.tree.format === 'LWO2' ) {

						this.parseForm( length );

					} else {

						this.parseClip( length );

					}

					break;
				case 'STIL':
					this.parseImage();
					break;
				case 'XREF':
					// clone of another STIL
					this.reader.skip( 8 ); // unknown
					this.currentForm.referenceTexture = {
						index: this.reader.getUint32(),
						refName: this.reader.getString() // internal unique ref
					};

					break;

					// Not in spec, used by texture nodes

				case 'IMST':
					this.parseImageStateForm( length );
					break;

					// SURF FORM AND SUB FORMS

				case 'SURF':
					this.parseSurfaceForm( length );
					break;
				case 'VALU':
					// Not in spec
					this.parseValueForm( length );
					break;
				case 'NTAG':
					this.parseSubNode( length );
					break;
				case 'ATTR': // BSDF Node Attributes
				case 'SATR':
					// Standard Node Attributes
					this.setupForm( 'attributes', length );
					break;
				case 'NCON':
					this.parseConnections( length );
					break;
				case 'SSHA':
					this.parentForm = this.currentForm;
					this.currentForm = this.currentSurface;
					this.setupForm( 'surfaceShader', length );
					break;
				case 'SSHD':
					this.setupForm( 'surfaceShaderData', length );
					break;
				case 'ENTR':
					// Not in spec
					this.parseEntryForm( length );
					break;

					// Image Map Layer

				case 'IMAP':
					this.parseImageMap( length );
					break;
				case 'TAMP':
					this.parseXVAL( 'amplitude', length );
					break;

					//Texture Mapping Form

				case 'TMAP':
					this.setupForm( 'textureMap', length );
					break;
				case 'CNTR':
					this.parseXVAL3( 'center', length );
					break;
				case 'SIZE':
					this.parseXVAL3( 'scale', length );
					break;
				case 'ROTA':
					this.parseXVAL3( 'rotation', length );
					break;
				default:
					this.parseUnknownForm( type, length );

			}

			this.debugger.node = 0;
			this.debugger.nodeID = type;
			this.debugger.log();

		},
		setupForm( type, length ) {

			if ( ! this.currentForm ) this.currentForm = this.currentNode;
			this.currentFormEnd = this.reader.offset + length;
			this.parentForm = this.currentForm;
			if ( ! this.currentForm[ type ] ) {

				this.currentForm[ type ] = {};
				this.currentForm = this.currentForm[ type ];

			} else {

				// should never see this unless there's a bug in the reader
				console.warn( 'LWOLoader: form already exists on parent: ', type, this.currentForm );
				this.currentForm = this.currentForm[ type ];

			}

		},
		skipForm( length ) {

			this.reader.skip( length - 4 );

		},
		parseUnknownForm( type, length ) {

			console.warn( 'LWOLoader: unknown FORM encountered: ' + type, length );
			printBuffer( this.reader.dv.buffer, this.reader.offset, length - 4 );
			this.reader.skip( length - 4 );

		},
		parseSurfaceForm( length ) {

			this.reader.skip( 8 ); // unknown Uint32 x2

			var name = this.reader.getString();
			var surface = {
				attributes: {},
				// LWO2 style non-node attributes will go here
				connections: {},
				name: name,
				inputName: name,
				nodes: {},
				source: this.reader.getString()
			};
			this.tree.materials[ name ] = surface;
			this.currentSurface = surface;
			this.parentForm = this.tree.materials;
			this.currentForm = surface;
			this.currentFormEnd = this.reader.offset + length;

		},
		parseSurfaceLwo2( length ) {

			var name = this.reader.getString();
			var surface = {
				attributes: {},
				// LWO2 style non-node attributes will go here
				connections: {},
				name: name,
				nodes: {},
				source: this.reader.getString()
			};
			this.tree.materials[ name ] = surface;
			this.currentSurface = surface;
			this.parentForm = this.tree.materials;
			this.currentForm = surface;
			this.currentFormEnd = this.reader.offset + length;

		},
		parseSubNode( length ) {

			// parse the NRNM CHUNK of the subnode FORM to get
			// a meaningful name for the subNode
			// some subnodes can be renamed, but Input and Surface cannot

			this.reader.skip( 8 ); // NRNM + length
			var name = this.reader.getString();
			var node = {
				name: name
			};
			this.currentForm = node;
			this.currentNode = node;
			this.currentFormEnd = this.reader.offset + length;

		},
		// collect attributes from all nodes at the top level of a surface
		parseConnections( length ) {

			this.currentFormEnd = this.reader.offset + length;
			this.parentForm = this.currentForm;
			this.currentForm = this.currentSurface.connections;

		},
		// surface node attribute data, e.g. specular, roughness etc
		parseEntryForm( length ) {

			this.reader.skip( 8 ); // NAME + length
			var name = this.reader.getString();
			this.currentForm = this.currentNode.attributes;
			this.setupForm( name, length );

		},
		// parse values from material - doesn't match up to other LWO3 data types
		// sub form of entry form
		parseValueForm() {

			this.reader.skip( 8 ); // unknown + length

			var valueType = this.reader.getString();
			if ( valueType === 'double' ) {

				this.currentForm.value = this.reader.getUint64();

			} else if ( valueType === 'int' ) {

				this.currentForm.value = this.reader.getUint32();

			} else if ( valueType === 'vparam' ) {

				this.reader.skip( 24 );
				this.currentForm.value = this.reader.getFloat64();

			} else if ( valueType === 'vparam3' ) {

				this.reader.skip( 24 );
				this.currentForm.value = this.reader.getFloat64Array( 3 );

			}

		},
		// holds various data about texture node image state
		// Data other thanmipMapLevel unknown
		parseImageStateForm() {

			this.reader.skip( 8 ); // unknown

			this.currentForm.mipMapLevel = this.reader.getFloat32();

		},
		// LWO2 style image data node OR LWO3 textures defined at top level in editor (not as SURF node)
		parseImageMap( length ) {

			this.currentFormEnd = this.reader.offset + length;
			this.parentForm = this.currentForm;
			if ( ! this.currentForm.maps ) this.currentForm.maps = [];
			var map = {};
			this.currentForm.maps.push( map );
			this.currentForm = map;
			this.reader.skip( 10 ); // unknown, could be an issue if it contains a VX

		},

		parseTextureNodeAttribute( type ) {

			this.reader.skip( 28 ); // FORM + length + VPRM + unknown + Uint32 x2 + float32

			this.reader.skip( 20 ); // FORM + length + VPVL + float32 + Uint32

			switch ( type ) {

				case 'ISCL':
					this.currentNode.scale = this.reader.getFloat32Array( 3 );
					break;
				case 'IPOS':
					this.currentNode.position = this.reader.getFloat32Array( 3 );
					break;
				case 'IROT':
					this.currentNode.rotation = this.reader.getFloat32Array( 3 );
					break;
				case 'IFAL':
					this.currentNode.falloff = this.reader.getFloat32Array( 3 );
					break;
				case 'IBMP':
					this.currentNode.amplitude = this.reader.getFloat32();
					break;
				case 'IUTD':
					this.currentNode.uTiles = this.reader.getFloat32();
					break;
				case 'IVTD':
					this.currentNode.vTiles = this.reader.getFloat32();
					break;

			}

			this.reader.skip( 2 ); // unknown

		},

		// ENVL forms are currently ignored
		parseEnvelope( length ) {

			this.reader.skip( length - 4 ); // skipping  entirely for now

		},

		///
		// CHUNK PARSING METHODS
		///

		// clips can either be defined inside a surface node, or at the top
		// level and they have a different format in each case
		parseClip( length ) {

			var tag = this.reader.getIDTag();

			// inside surface node
			if ( tag === 'FORM' ) {

				this.reader.skip( 16 );
				this.currentNode.fileName = this.reader.getString();
				return;

			}

			// otherwise top level
			this.reader.setOffset( this.reader.offset - 4 );
			this.currentFormEnd = this.reader.offset + length;
			this.parentForm = this.currentForm;
			this.reader.skip( 8 ); // unknown

			var texture = {
				index: this.reader.getUint32()
			};
			this.tree.textures.push( texture );
			this.currentForm = texture;

		},
		parseClipLwo2( length ) {

			var texture = {
				index: this.reader.getUint32(),
				fileName: ''
			};

			// seach STIL block
			while ( true ) {

				var tag = this.reader.getIDTag();
				var n_length = this.reader.getUint16();
				if ( tag === 'STIL' ) {

					texture.fileName = this.reader.getString();
					break;

				}

				if ( n_length >= length ) {

					break;

				}

			}

			this.tree.textures.push( texture );
			this.currentForm = texture;

		},
		parseImage() {

			this.reader.skip( 8 ); // unknown
			this.currentForm.fileName = this.reader.getString();

		},
		parseXVAL( type, length ) {

			var endOffset = this.reader.offset + length - 4;
			this.reader.skip( 8 );
			this.currentForm[ type ] = this.reader.getFloat32();
			this.reader.setOffset( endOffset ); // set end offset directly to skip optional envelope

		},

		parseXVAL3( type, length ) {

			var endOffset = this.reader.offset + length - 4;
			this.reader.skip( 8 );
			this.currentForm[ type ] = {
				x: this.reader.getFloat32(),
				y: this.reader.getFloat32(),
				z: this.reader.getFloat32()
			};
			this.reader.setOffset( endOffset );

		},
		// Tags associated with an object
		// OTAG { type[ID4], tag-string[S0] }
		parseObjectTag() {

			if ( ! this.tree.objectTags ) this.tree.objectTags = {};
			this.tree.objectTags[ this.reader.getIDTag() ] = {
				tagString: this.reader.getString()
			};

		},
		// Signals the start of a new layer. All the data chunks which follow will be included in this layer until another layer chunk is encountered.
		// LAYR: number[U2], flags[U2], pivot[VEC12], name[S0], parent[U2]
		parseLayer( length ) {

			var layer = {
				number: this.reader.getUint16(),
				flags: this.reader.getUint16(),
				// If the least significant bit of flags is set, the layer is hidden.
				pivot: this.reader.getFloat32Array( 3 ),
				// Note: this seems to be superflous, as the geometry is translated when pivot is present
				name: this.reader.getString()
			};
			this.tree.layers.push( layer );
			this.currentLayer = layer;
			var parsedLength = 16 + stringOffset( this.currentLayer.name ); // index ( 2 ) + flags( 2 ) + pivot( 12 ) + stringlength

			// if we have not reached then end of the layer block, there must be a parent defined
			this.currentLayer.parent = parsedLength < length ? this.reader.getUint16() : - 1; // omitted or -1 for no parent

		},

		// VEC12 * ( F4 + F4 + F4 ) array of x,y,z vectors
		// Converting from left to right handed coordinate system:
		// x -> -x and switch material FrontSide -> BackSide
		parsePoints( length ) {

			this.currentPoints = [];
			for ( var i = 0; i < length / 4; i += 3 ) {

				// z -> -z to match three.js right handed coords
				this.currentPoints.push( this.reader.getFloat32(), this.reader.getFloat32(), - this.reader.getFloat32() );

			}

		},
		// parse VMAP or VMAD
		// Associates a set of floating-point vectors with a set of points.
		// VMAP: { type[ID4], dimension[U2], name[S0], ( vert[VX], value[F4] # dimension ) * }

		// VMAD Associates a set of floating-point vectors with the vertices of specific polygons.
		// Similar to VMAP UVs, but associates with polygon vertices rather than points
		// to solve to problem of UV seams:  VMAD chunks are paired with VMAPs of the same name,
		// if they exist. The vector values in the VMAD will then replace those in the
		// corresponding VMAP, but only for calculations involving the specified polygons.
		// VMAD { type[ID4], dimension[U2], name[S0], ( vert[VX], poly[VX], value[F4] # dimension ) * }
		parseVertexMapping( length, discontinuous ) {

			var finalOffset = this.reader.offset + length;
			var channelName = this.reader.getString();
			if ( this.reader.offset === finalOffset ) {

				// then we are in a texture node and the VMAP chunk is just a reference to a UV channel name
				this.currentForm.UVChannel = channelName;
				return;

			}

			// otherwise reset to initial length and parse normal VMAP CHUNK
			this.reader.setOffset( this.reader.offset - stringOffset( channelName ) );
			var type = this.reader.getIDTag();
			this.reader.getUint16(); // dimension
			var name = this.reader.getString();
			var remainingLength = length - 6 - stringOffset( name );
			switch ( type ) {

				case 'TXUV':
					this.parseUVMapping( name, finalOffset, discontinuous );
					break;
				case 'MORF':
				case 'SPOT':
					this.parseMorphTargets( name, finalOffset, type ); // can't be discontinuous
					break;
					// unsupported VMAPs
				case 'APSL':
				case 'NORM':
				case 'WGHT':
				case 'MNVW':
				case 'PICK':
				case 'RGB ':
				case 'RGBA':
					this.reader.skip( remainingLength );
					break;
				default:
					console.warn( 'LWOLoader: unknown vertex map type: ' + type );
					this.reader.skip( remainingLength );

			}

		},
		parseUVMapping( name, finalOffset, discontinuous ) {

			var uvIndices = [];
			var polyIndices = [];
			var uvs = [];
			while ( this.reader.offset < finalOffset ) {

				uvIndices.push( this.reader.getVariableLengthIndex() );
				if ( discontinuous ) polyIndices.push( this.reader.getVariableLengthIndex() );
				uvs.push( this.reader.getFloat32(), this.reader.getFloat32() );

			}

			if ( discontinuous ) {

				if ( ! this.currentLayer.discontinuousUVs ) this.currentLayer.discontinuousUVs = {};
				this.currentLayer.discontinuousUVs[ name ] = {
					uvIndices: uvIndices,
					polyIndices: polyIndices,
					uvs: uvs
				};

			} else {

				if ( ! this.currentLayer.uvs ) this.currentLayer.uvs = {};
				this.currentLayer.uvs[ name ] = {
					uvIndices: uvIndices,
					uvs: uvs
				};

			}

		},
		parseMorphTargets( name, finalOffset, type ) {

			var indices = [];
			var points = [];
			type = type === 'MORF' ? 'relative' : 'absolute';
			while ( this.reader.offset < finalOffset ) {

				indices.push( this.reader.getVariableLengthIndex() );
				// z -> -z to match three.js right handed coords
				points.push( this.reader.getFloat32(), this.reader.getFloat32(), - this.reader.getFloat32() );

			}

			if ( ! this.currentLayer.morphTargets ) this.currentLayer.morphTargets = {};
			this.currentLayer.morphTargets[ name ] = {
				indices: indices,
				points: points,
				type: type
			};

		},
		// A list of polygons for the current layer.
		// POLS { type[ID4], ( numvert+flags[U2], vert[VX] # numvert ) * }
		parsePolygonList( length ) {

			var finalOffset = this.reader.offset + length;
			var type = this.reader.getIDTag();
			var indices = [];

			// hold a list of polygon sizes, to be split up later
			var polygonDimensions = [];
			while ( this.reader.offset < finalOffset ) {

				var numverts = this.reader.getUint16();

				//var flags = numverts & 64512; // 6 high order bits are flags - ignoring for now
				numverts = numverts & 1023; // remaining ten low order bits are vertex num
				polygonDimensions.push( numverts );
				for ( var j = 0; j < numverts; j ++ ) indices.push( this.reader.getVariableLengthIndex() );

			}

			var geometryData = {
				type: type,
				vertexIndices: indices,
				polygonDimensions: polygonDimensions,
				points: this.currentPoints
			};

			// Note: assuming that all polys will be lines or points if the first is
			if ( polygonDimensions[ 0 ] === 1 ) geometryData.type = 'points'; else if ( polygonDimensions[ 0 ] === 2 ) geometryData.type = 'lines';
			this.currentLayer.geometry = geometryData;

		},
		// Lists the tag strings that can be associated with polygons by the PTAG chunk.
		// TAGS { tag-string[S0] * }
		parseTagStrings( length ) {

			this.tree.tags = this.reader.getStringArray( length );

		},
		// Associates tags of a given type with polygons in the most recent POLS chunk.
		// PTAG { type[ID4], ( poly[VX], tag[U2] ) * }
		parsePolygonTagMapping( length ) {

			var finalOffset = this.reader.offset + length;
			var type = this.reader.getIDTag();
			if ( type === 'SURF' ) this.parseMaterialIndices( finalOffset ); else {

				//PART, SMGP, COLR not supported

				this.reader.skip( length - 4 );

			}

		},
		parseMaterialIndices( finalOffset ) {

			// array holds polygon index followed by material index
			this.currentLayer.geometry.materialIndices = [];
			while ( this.reader.offset < finalOffset ) {

				var polygonIndex = this.reader.getVariableLengthIndex();
				var materialIndex = this.reader.getUint16();
				this.currentLayer.geometry.materialIndices.push( polygonIndex, materialIndex );

			}

		},
		parseUnknownCHUNK( blockID, length ) {

			console.warn( 'LWOLoader: unknown chunk type: ' + blockID + ' length: ' + length );

			// print the chunk plus some bytes padding either side
			// printBuffer( this.reader.dv.buffer, this.reader.offset - 20, length + 40 );

			var data = this.reader.getString( length );
			this.currentForm[ blockID ] = data;

		}
	};
	function DataViewReader( buffer ) {

		this.dv = new DataView( buffer );
		this.offset = 0;

	}

	DataViewReader.prototype = {
		constructor: DataViewReader,
		size: function () {

			return this.dv.buffer.byteLength;

		},
		setOffset( offset ) {

			if ( offset > 0 && offset < this.dv.buffer.byteLength ) {

				this.offset = offset;

			} else {

				console.error( 'LWOLoader: invalid buffer offset' );

			}

		},
		endOfFile: function () {

			if ( this.offset >= this.size() ) return true;
			return false;

		},
		skip: function ( length ) {

			this.offset += length;

		},
		getUint8: function () {

			var value = this.dv.getUint8( this.offset );
			this.offset += 1;
			return value;

		},
		getUint16: function () {

			var value = this.dv.getUint16( this.offset );
			this.offset += 2;
			return value;

		},
		getInt32: function () {

			var value = this.dv.getInt32( this.offset, false );
			this.offset += 4;
			return value;

		},
		getUint32: function () {

			var value = this.dv.getUint32( this.offset, false );
			this.offset += 4;
			return value;

		},
		getUint64: function () {

			var low, high;
			high = this.getUint32();
			low = this.getUint32();
			return high * 0x100000000 + low;

		},
		getFloat32: function () {

			var value = this.dv.getFloat32( this.offset, false );
			this.offset += 4;
			return value;

		},
		getFloat32Array: function ( size ) {

			var a = [];
			for ( var i = 0; i < size; i ++ ) {

				a.push( this.getFloat32() );

			}

			return a;

		},
		getFloat64: function () {

			var value = this.dv.getFloat64( this.offset, this.littleEndian );
			this.offset += 8;
			return value;

		},
		getFloat64Array: function ( size ) {

			var a = [];
			for ( var i = 0; i < size; i ++ ) {

				a.push( this.getFloat64() );

			}

			return a;

		},
		// get variable-length index data type
		// VX ::= index[U2] | (index + 0xFF000000)[U4]
		// If the index value is less than 65,280 (0xFF00),then VX === U2
		// otherwise VX === U4 with bits 24-31 set
		// When reading an index, if the first byte encountered is 255 (0xFF), then
		// the four-byte form is being used and the first byte should be discarded or masked out.
		getVariableLengthIndex() {

			var firstByte = this.getUint8();
			if ( firstByte === 255 ) {

				return this.getUint8() * 65536 + this.getUint8() * 256 + this.getUint8();

			}

			return firstByte * 256 + this.getUint8();

		},
		// An ID tag is a sequence of 4 bytes containing 7-bit ASCII values
		getIDTag() {

			return this.getString( 4 );

		},
		getString: function ( size ) {

			if ( size === 0 ) return;

			// note: safari 9 doesn't support Uint8Array.indexOf; create intermediate array instead
			var a = [];
			if ( size ) {

				for ( var i = 0; i < size; i ++ ) {

					a[ i ] = this.getUint8();

				}

			} else {

				var currentChar;
				var len = 0;
				while ( currentChar !== 0 ) {

					currentChar = this.getUint8();
					if ( currentChar !== 0 ) a.push( currentChar );
					len ++;

				}

				if ( ! isEven( len + 1 ) ) this.getUint8(); // if string with terminating nullbyte is uneven, extra nullbyte is added

			}

			return THREE.LoaderUtils.decodeText( new Uint8Array( a ) );

		},
		getStringArray: function ( size ) {

			var a = this.getString( size );
			a = a.split( '\0' );
			return a.filter( Boolean ); // return array with any empty strings removed

		}
	};

	// ************** DEBUGGER  **************

	function Debugger() {

		this.active = false;
		this.depth = 0;
		this.formList = [];

	}

	Debugger.prototype = {
		constructor: Debugger,
		enable: function () {

			this.active = true;

		},
		log: function () {

			if ( ! this.active ) return;
			var nodeType;
			switch ( this.node ) {

				case 0:
					nodeType = 'FORM';
					break;
				case 1:
					nodeType = 'CHK';
					break;
				case 2:
					nodeType = 'S-CHK';
					break;

			}

			console.log( '| '.repeat( this.depth ) + nodeType, this.nodeID, `( ${this.offset} ) -> ( ${this.dataOffset + this.length} )`, this.node == 0 ? ' {' : '', this.skipped ? 'SKIPPED' : '', this.node == 0 && this.skipped ? '}' : '' );
			if ( this.node == 0 && ! this.skipped ) {

				this.depth += 1;
				this.formList.push( this.dataOffset + this.length );

			}

			this.skipped = false;

		},
		closeForms: function () {

			if ( ! this.active ) return;
			for ( var i = this.formList.length - 1; i >= 0; i -- ) {

				if ( this.offset >= this.formList[ i ] ) {

					this.depth -= 1;
					console.log( '| '.repeat( this.depth ) + '}' );
					this.formList.splice( - 1, 1 );

				}

			}

		}
	};

	// ************** UTILITY FUNCTIONS **************

	function isEven( num ) {

		return num % 2;

	}

	// calculate the length of the string in the buffer
	// this will be string.length + nullbyte + optional padbyte to make the length even
	function stringOffset( string ) {

		return string.length + 1 + ( isEven( string.length + 1 ) ? 1 : 0 );

	}

	// for testing purposes, dump buffer to console
	// printBuffer( this.reader.dv.buffer, this.reader.offset, length );
	function printBuffer( buffer, from, to ) {

		console.log( THREE.LoaderUtils.decodeText( new Uint8Array( buffer, from, to ) ) );

	}

	THREE.IFFParser = IFFParser;

} )();