/**
 *  Forked from code from com.adobe.images.JPGEncoder in as3corelib under the license contained
 *  in that file to produce a derivative work.
 *
 *  see:
 *  http://code.google.com/p/as3corelib/source/browse/trunk/src/com/adobe/images/JPGEncoder.as?r=25
*/
package com.threerings.flash
{
    
import flash.geom.*;
import flash.display.*;
import flash.utils.*;

/**
 * Class for compressing bitmaps into jpegs.  Each instance may only be used for a single image.
 * When the encoder is constructed, the headers are generated, but no pixel encoding is done.
 * Subsequent calls to 'process' will encode pixels for a specified length of time.  Once the
 * encoding is done (determined by process returning true, or a call to isComplete), the jpeg data
 * can be accessed via getJpeg.
 */		
public class JPGEncoder
{    
	// Static table initialization

	private var ZigZag:Array = [
		 0, 1, 5, 6,14,15,27,28,
		 2, 4, 7,13,16,26,29,42,
		 3, 8,12,17,25,30,41,43,
		 9,11,18,24,31,40,44,53,
		10,19,23,32,39,45,52,54,
		20,22,33,38,46,51,55,60,
		21,34,37,47,50,56,59,61,
		35,36,48,49,57,58,62,63
	];

	private var YTable:Array = new Array(64);
	private var UVTable:Array = new Array(64);
	private var fdtbl_Y:Array = new Array(64);
	private var fdtbl_UV:Array = new Array(64);

	private function initQuantTables(sf:int):void
	{
		var i:int;
		var t:Number;
		var YQT:Array = [
			16, 11, 10, 16, 24, 40, 51, 61,
			12, 12, 14, 19, 26, 58, 60, 55,
			14, 13, 16, 24, 40, 57, 69, 56,
			14, 17, 22, 29, 51, 87, 80, 62,
			18, 22, 37, 56, 68,109,103, 77,
			24, 35, 55, 64, 81,104,113, 92,
			49, 64, 78, 87,103,121,120,101,
			72, 92, 95, 98,112,100,103, 99
		];
		for (i = 0; i < 64; i++) {
			t = Math.floor((YQT[i]*sf+50)/100);
			if (t < 1) {
				t = 1;
			} else if (t > 255) {
				t = 255;
			}
			YTable[ZigZag[i]] = t;
		}
		var UVQT:Array = [
			17, 18, 24, 47, 99, 99, 99, 99,
			18, 21, 26, 66, 99, 99, 99, 99,
			24, 26, 56, 99, 99, 99, 99, 99,
			47, 66, 99, 99, 99, 99, 99, 99,
			99, 99, 99, 99, 99, 99, 99, 99,
			99, 99, 99, 99, 99, 99, 99, 99,
			99, 99, 99, 99, 99, 99, 99, 99,
			99, 99, 99, 99, 99, 99, 99, 99
		];
		for (i = 0; i < 64; i++) {
			t = Math.floor((UVQT[i]*sf+50)/100);
			if (t < 1) {
				t = 1;
			} else if (t > 255) {
				t = 255;
			}
			UVTable[ZigZag[i]] = t;
		}
		var aasf:Array = [
			1.0, 1.387039845, 1.306562965, 1.175875602,
			1.0, 0.785694958, 0.541196100, 0.275899379
		];
		i = 0;
		for (var row:int = 0; row < 8; row++)
		{
			for (var col:int = 0; col < 8; col++)
			{
				fdtbl_Y[i]  = (1.0 / (YTable [ZigZag[i]] * aasf[row] * aasf[col] * 8.0));
				fdtbl_UV[i] = (1.0 / (UVTable[ZigZag[i]] * aasf[row] * aasf[col] * 8.0));
				i++;
			}
		}
	}

	private var YDC_HT:Array;
	private var UVDC_HT:Array;
	private var YAC_HT:Array;
	private var UVAC_HT:Array;

	private function computeHuffmanTbl(nrcodes:Array, std_table:Array):Array
	{
		var codevalue:int = 0;
		var pos_in_table:int = 0;
		var HT:Array = new Array();
		for (var k:int=1; k<=16; k++) {
			for (var j:int=1; j<=nrcodes[k]; j++) {
				HT[std_table[pos_in_table]] = new BitString();
				HT[std_table[pos_in_table]].val = codevalue;
				HT[std_table[pos_in_table]].len = k;
				pos_in_table++;
				codevalue++;
			}
			codevalue*=2;
		}
		return HT;
	}

	private var std_dc_luminance_nrcodes:Array = [0,0,1,5,1,1,1,1,1,1,0,0,0,0,0,0,0];
	private var std_dc_luminance_values:Array = [0,1,2,3,4,5,6,7,8,9,10,11];
	private var std_ac_luminance_nrcodes:Array = [0,0,2,1,3,3,2,4,3,5,5,4,4,0,0,1,0x7d];
	private var std_ac_luminance_values:Array = [
		0x01,0x02,0x03,0x00,0x04,0x11,0x05,0x12,
		0x21,0x31,0x41,0x06,0x13,0x51,0x61,0x07,
		0x22,0x71,0x14,0x32,0x81,0x91,0xa1,0x08,
		0x23,0x42,0xb1,0xc1,0x15,0x52,0xd1,0xf0,
		0x24,0x33,0x62,0x72,0x82,0x09,0x0a,0x16,
		0x17,0x18,0x19,0x1a,0x25,0x26,0x27,0x28,
		0x29,0x2a,0x34,0x35,0x36,0x37,0x38,0x39,
		0x3a,0x43,0x44,0x45,0x46,0x47,0x48,0x49,
		0x4a,0x53,0x54,0x55,0x56,0x57,0x58,0x59,
		0x5a,0x63,0x64,0x65,0x66,0x67,0x68,0x69,
		0x6a,0x73,0x74,0x75,0x76,0x77,0x78,0x79,
		0x7a,0x83,0x84,0x85,0x86,0x87,0x88,0x89,
		0x8a,0x92,0x93,0x94,0x95,0x96,0x97,0x98,
		0x99,0x9a,0xa2,0xa3,0xa4,0xa5,0xa6,0xa7,
		0xa8,0xa9,0xaa,0xb2,0xb3,0xb4,0xb5,0xb6,
		0xb7,0xb8,0xb9,0xba,0xc2,0xc3,0xc4,0xc5,
		0xc6,0xc7,0xc8,0xc9,0xca,0xd2,0xd3,0xd4,
		0xd5,0xd6,0xd7,0xd8,0xd9,0xda,0xe1,0xe2,
		0xe3,0xe4,0xe5,0xe6,0xe7,0xe8,0xe9,0xea,
		0xf1,0xf2,0xf3,0xf4,0xf5,0xf6,0xf7,0xf8,
		0xf9,0xfa
	];

	private var std_dc_chrominance_nrcodes:Array = [0,0,3,1,1,1,1,1,1,1,1,1,0,0,0,0,0];
	private var std_dc_chrominance_values:Array = [0,1,2,3,4,5,6,7,8,9,10,11];
	private var std_ac_chrominance_nrcodes:Array = [0,0,2,1,2,4,4,3,4,7,5,4,4,0,1,2,0x77];
	private var std_ac_chrominance_values:Array = [
		0x00,0x01,0x02,0x03,0x11,0x04,0x05,0x21,
		0x31,0x06,0x12,0x41,0x51,0x07,0x61,0x71,
		0x13,0x22,0x32,0x81,0x08,0x14,0x42,0x91,
		0xa1,0xb1,0xc1,0x09,0x23,0x33,0x52,0xf0,
		0x15,0x62,0x72,0xd1,0x0a,0x16,0x24,0x34,
		0xe1,0x25,0xf1,0x17,0x18,0x19,0x1a,0x26,
		0x27,0x28,0x29,0x2a,0x35,0x36,0x37,0x38,
		0x39,0x3a,0x43,0x44,0x45,0x46,0x47,0x48,
		0x49,0x4a,0x53,0x54,0x55,0x56,0x57,0x58,
		0x59,0x5a,0x63,0x64,0x65,0x66,0x67,0x68,
		0x69,0x6a,0x73,0x74,0x75,0x76,0x77,0x78,
		0x79,0x7a,0x82,0x83,0x84,0x85,0x86,0x87,
		0x88,0x89,0x8a,0x92,0x93,0x94,0x95,0x96,
		0x97,0x98,0x99,0x9a,0xa2,0xa3,0xa4,0xa5,
		0xa6,0xa7,0xa8,0xa9,0xaa,0xb2,0xb3,0xb4,
		0xb5,0xb6,0xb7,0xb8,0xb9,0xba,0xc2,0xc3,
		0xc4,0xc5,0xc6,0xc7,0xc8,0xc9,0xca,0xd2,
		0xd3,0xd4,0xd5,0xd6,0xd7,0xd8,0xd9,0xda,
		0xe2,0xe3,0xe4,0xe5,0xe6,0xe7,0xe8,0xe9,
		0xea,0xf2,0xf3,0xf4,0xf5,0xf6,0xf7,0xf8,
		0xf9,0xfa
	];

	private function initHuffmanTbl():void
	{
		YDC_HT = computeHuffmanTbl(std_dc_luminance_nrcodes,std_dc_luminance_values);
		UVDC_HT = computeHuffmanTbl(std_dc_chrominance_nrcodes,std_dc_chrominance_values);
		YAC_HT = computeHuffmanTbl(std_ac_luminance_nrcodes,std_ac_luminance_values);
		UVAC_HT = computeHuffmanTbl(std_ac_chrominance_nrcodes,std_ac_chrominance_values);
	}

	private var bitcode:Array = new Array(65535);
	private var category:Array = new Array(65535);

	private function initCategoryNumber():void
	{
		var nrlower:int = 1;
		var nrupper:int = 2;
		var nr:int;
		for (var cat:int=1; cat<=15; cat++) {
			//Positive numbers
			for (nr=nrlower; nr<nrupper; nr++) {
				category[32767+nr] = cat;
				bitcode[32767+nr] = new BitString();
				bitcode[32767+nr].len = cat;
				bitcode[32767+nr].val = nr;
			}
			//Negative numbers
			for (nr=-(nrupper-1); nr<=-nrlower; nr++) {
				category[32767+nr] = cat;
				bitcode[32767+nr] = new BitString();
				bitcode[32767+nr].len = cat;
				bitcode[32767+nr].val = nrupper-1+nr;
			}
			nrlower <<= 1;
			nrupper <<= 1;
		}
	}

	private function writeBits(bs:BitString):void
	{
		var value:int = bs.val;
		var posval:int = bs.len-1;
		while ( posval >= 0 ) {
			if (value & uint(1 << posval) ) {
				_bytenew |= uint(1 << _bytepos);
			}
			posval--;
			_bytepos--;
			if (_bytepos < 0) {
				if (_bytenew == 0xFF) {
					writeByte(0xFF);
					writeByte(0);
				}
				else {
					writeByte(_bytenew);
				}
				_bytepos=7;
				_bytenew=0;
			}
		}
	}

	private function writeByte(value:int):void
	{
		_byteout.writeByte(value);
	}

	private function writeWord(value:int):void
	{
		writeByte((value>>8)&0xFF);
		writeByte((value   )&0xFF);
	}

	// DCT & quantization core

	private function fDCTQuant(data:Array, fdtbl:Array):Array
	{
		var tmp0:Number, tmp1:Number, tmp2:Number, tmp3:Number, tmp4:Number, tmp5:Number, tmp6:Number, tmp7:Number;
		var tmp10:Number, tmp11:Number, tmp12:Number, tmp13:Number;
		var z1:Number, z2:Number, z3:Number, z4:Number, z5:Number, z11:Number, z13:Number;
		var i:int;
		/* Pass 1: process rows. */
		var dataOff:int=0;
		for (i=0; i<8; i++) {
			tmp0 = data[dataOff+0] + data[dataOff+7];
			tmp7 = data[dataOff+0] - data[dataOff+7];
			tmp1 = data[dataOff+1] + data[dataOff+6];
			tmp6 = data[dataOff+1] - data[dataOff+6];
			tmp2 = data[dataOff+2] + data[dataOff+5];
			tmp5 = data[dataOff+2] - data[dataOff+5];
			tmp3 = data[dataOff+3] + data[dataOff+4];
			tmp4 = data[dataOff+3] - data[dataOff+4];

			/* Even part */
			tmp10 = tmp0 + tmp3;	/* phase 2 */
			tmp13 = tmp0 - tmp3;
			tmp11 = tmp1 + tmp2;
			tmp12 = tmp1 - tmp2;

			data[dataOff+0] = tmp10 + tmp11; /* phase 3 */
			data[dataOff+4] = tmp10 - tmp11;

			z1 = (tmp12 + tmp13) * 0.707106781; /* c4 */
			data[dataOff+2] = tmp13 + z1; /* phase 5 */
			data[dataOff+6] = tmp13 - z1;

			/* Odd part */
			tmp10 = tmp4 + tmp5; /* phase 2 */
			tmp11 = tmp5 + tmp6;
			tmp12 = tmp6 + tmp7;

			/* The rotator is modified from fig 4-8 to avoid extra negations. */
			z5 = (tmp10 - tmp12) * 0.382683433; /* c6 */
			z2 = 0.541196100 * tmp10 + z5; /* c2-c6 */
			z4 = 1.306562965 * tmp12 + z5; /* c2+c6 */
			z3 = tmp11 * 0.707106781; /* c4 */

			z11 = tmp7 + z3;	/* phase 5 */
			z13 = tmp7 - z3;

			data[dataOff+5] = z13 + z2;	/* phase 6 */
			data[dataOff+3] = z13 - z2;
			data[dataOff+1] = z11 + z4;
			data[dataOff+7] = z11 - z4;

			dataOff += 8; /* advance pointer to next row */
		}

		/* Pass 2: process columns. */
		dataOff = 0;
		for (i=0; i<8; i++) {
			tmp0 = data[dataOff+ 0] + data[dataOff+56];
			tmp7 = data[dataOff+ 0] - data[dataOff+56];
			tmp1 = data[dataOff+ 8] + data[dataOff+48];
			tmp6 = data[dataOff+ 8] - data[dataOff+48];
			tmp2 = data[dataOff+16] + data[dataOff+40];
			tmp5 = data[dataOff+16] - data[dataOff+40];
			tmp3 = data[dataOff+24] + data[dataOff+32];
			tmp4 = data[dataOff+24] - data[dataOff+32];

			/* Even part */
			tmp10 = tmp0 + tmp3;	/* phase 2 */
			tmp13 = tmp0 - tmp3;
			tmp11 = tmp1 + tmp2;
			tmp12 = tmp1 - tmp2;

			data[dataOff+ 0] = tmp10 + tmp11; /* phase 3 */
			data[dataOff+32] = tmp10 - tmp11;

			z1 = (tmp12 + tmp13) * 0.707106781; /* c4 */
			data[dataOff+16] = tmp13 + z1; /* phase 5 */
			data[dataOff+48] = tmp13 - z1;

			/* Odd part */
			tmp10 = tmp4 + tmp5; /* phase 2 */
			tmp11 = tmp5 + tmp6;
			tmp12 = tmp6 + tmp7;

			/* The rotator is modified from fig 4-8 to avoid extra negations. */
			z5 = (tmp10 - tmp12) * 0.382683433; /* c6 */
			z2 = 0.541196100 * tmp10 + z5; /* c2-c6 */
			z4 = 1.306562965 * tmp12 + z5; /* c2+c6 */
			z3 = tmp11 * 0.707106781; /* c4 */

			z11 = tmp7 + z3;	/* phase 5 */
			z13 = tmp7 - z3;

			data[dataOff+40] = z13 + z2; /* phase 6 */
			data[dataOff+24] = z13 - z2;
			data[dataOff+ 8] = z11 + z4;
			data[dataOff+56] = z11 - z4;

			dataOff++; /* advance pointer to next column */
		}

		// Quantize/descale the coefficients
		for (i=0; i<64; i++) {
			// Apply the quantization and scaling factor & Round to nearest integer
			data[i] = Math.round((data[i]*fdtbl[i]));
		}
		return data;
	}

	// Chunk writing

	private function writeAPP0():void
	{
		writeWord(0xFFE0); // marker
		writeWord(16); // length
		writeByte(0x4A); // J
		writeByte(0x46); // F
		writeByte(0x49); // I
		writeByte(0x46); // F
		writeByte(0); // = "JFIF",'\0'
		writeByte(1); // versionhi
		writeByte(1); // versionlo
		writeByte(0); // xyunits
		writeWord(1); // xdensity
		writeWord(1); // ydensity
		writeByte(0); // thumbnwidth
		writeByte(0); // thumbnheight
	}

	private function writeSOF0(width:int, height:int):void
	{
		writeWord(0xFFC0); // marker
		writeWord(17);   // length, truecolor YUV JPG
		writeByte(8);    // precision
		writeWord(height);
		writeWord(width);
		writeByte(3);    // nrofcomponents
		writeByte(1);    // IdY
		writeByte(0x11); // HVY
		writeByte(0);    // QTY
		writeByte(2);    // IdU
		writeByte(0x11); // HVU
		writeByte(1);    // QTU
		writeByte(3);    // IdV
		writeByte(0x11); // HVV
		writeByte(1);    // QTV
	}

	private function writeDQT():void
	{
		writeWord(0xFFDB); // marker
		writeWord(132);	   // length
		writeByte(0);
		var i:int;
		for (i=0; i<64; i++) {
			writeByte(YTable[i]);
		}
		writeByte(1);
		for (i=0; i<64; i++) {
			writeByte(UVTable[i]);
		}
	}

	private function writeDHT():void
	{
		writeWord(0xFFC4); // marker
		writeWord(0x01A2); // length
		var i:int;

		writeByte(0); // HTYDCinfo
		for (i=0; i<16; i++) {
			writeByte(std_dc_luminance_nrcodes[i+1]);
		}
		for (i=0; i<=11; i++) {
			writeByte(std_dc_luminance_values[i]);
		}

		writeByte(0x10); // HTYACinfo
		for (i=0; i<16; i++) {
			writeByte(std_ac_luminance_nrcodes[i+1]);
		}
		for (i=0; i<=161; i++) {
			writeByte(std_ac_luminance_values[i]);
		}

		writeByte(1); // HTUDCinfo
		for (i=0; i<16; i++) {
			writeByte(std_dc_chrominance_nrcodes[i+1]);
		}
		for (i=0; i<=11; i++) {
			writeByte(std_dc_chrominance_values[i]);
		}

		writeByte(0x11); // HTUACinfo
		for (i=0; i<16; i++) {
			writeByte(std_ac_chrominance_nrcodes[i+1]);
		}
		for (i=0; i<=161; i++) {
			writeByte(std_ac_chrominance_values[i]);
		}
	}

	private function writeSOS():void
	{
		writeWord(0xFFDA); // marker
		writeWord(12); // length
		writeByte(3); // nrofcomponents
		writeByte(1); // IdY
		writeByte(0); // HTY
		writeByte(2); // IdU
		writeByte(0x11); // HTU
		writeByte(3); // IdV
		writeByte(0x11); // HTV
		writeByte(0); // Ss
		writeByte(0x3f); // Se
		writeByte(0); // Bf
	}

	// Core processing
	private var DU:Array = new Array(64);

	private function processDU(CDU:Array, fdtbl:Array, DC:Number, HTDC:Array, HTAC:Array):Number
	{
		var EOB:BitString = HTAC[0x00];
		var M16zeroes:BitString = HTAC[0xF0];
		var i:int;

		var DU_DCT:Array = fDCTQuant(CDU, fdtbl);
		//ZigZag reorder
		for (i=0;i<64;i++) {
			DU[ZigZag[i]]=DU_DCT[i];
		}
		var Diff:int = DU[0] - DC; DC = DU[0];
		//Encode DC
		if (Diff==0) {
			writeBits(HTDC[0]); // Diff might be 0
		} else {
			writeBits(HTDC[category[32767+Diff]]);
			writeBits(bitcode[32767+Diff]);
		}
		//Encode ACs
		var end0pos:int = 63;
		for (; (end0pos>0)&&(DU[end0pos]==0); end0pos--) {
		};
		//end0pos = first element in reverse order !=0
		if ( end0pos == 0) {
			writeBits(EOB);
			return DC;
		}
		i = 1;
		while ( i <= end0pos ) {
			var startpos:int = i;
			for (; (DU[i]==0) && (i<=end0pos); i++) {
			}
			var nrzeroes:int = i-startpos;
			if ( nrzeroes >= 16 ) {
				for (var nrmarker:int=1; nrmarker <= nrzeroes/16; nrmarker++) {
					writeBits(M16zeroes);
				}
				nrzeroes = int(nrzeroes&0xF);
			}
			writeBits(HTAC[nrzeroes*16+category[32767+DU[i]]]);
			writeBits(bitcode[32767+DU[i]]);
			i++;
		}
		if ( end0pos != 63 ) {
			writeBits(EOB);
		}
		return DC;
	}

	private var YDU:Array = new Array(64);
	private var UDU:Array = new Array(64);
	private var VDU:Array = new Array(64);

	private function RGB2YUV(img:BitmapData, xpos:int, ypos:int):void
	{
		var pos:int=0;
		for (var y:int=0; y<8; y++) {
			for (var x:int=0; x<8; x++) {
				var P:uint = img.getPixel32(xpos+x,ypos+y);
				var R:Number = Number((P>>16)&0xFF);
				var G:Number = Number((P>> 8)&0xFF);
				var B:Number = Number((P    )&0xFF);
				YDU[pos]=((( 0.29900)*R+( 0.58700)*G+( 0.11400)*B))-128;
				UDU[pos]=(((-0.16874)*R+(-0.33126)*G+( 0.50000)*B));
				VDU[pos]=((( 0.50000)*R+(-0.41869)*G+(-0.08131)*B));
				pos++;
			}
		}
	}

	/**
	 * Construct a new JPGEncoder object.
	 * 
	 * @param image The image to encode
	 * @param quality Quality level between 1 and 100 determining the level of compression.s
	 * @param pixelGranularity The minumum number of pixels to process at a time.
	 */		
	public function JPGEncoder(image :BitmapData, quality :Number = 50, pixelGranularity :int = 100)
	{
	    _image = image;
	    _pixelGranularity = pixelGranularity;
	    
		if (quality <= 0) {
			quality = 1;
		}
		if (quality > 100) {
			quality = 100;
		}
		var sf:int = 0;
		if (quality < 50) {
			sf = int(5000 / quality);
		} else {
			sf = int(200 - quality*2);
		}
		// Create tables
		initHuffmanTbl();
		initCategoryNumber();
		initQuantTables(sf);
		
		writeHeader();
		initializeEncoding();	    
	}
	
	/**
	 * Write the jpeg header into the byte array for output.
	 */
	protected function writeHeader () :void
	{
		// Initialize bit writer
		_bytenew=0;
		_bytepos=7;

		// Add JPEG headers
		writeWord(0xFFD8); // SOI
		writeAPP0();
		writeDQT();
		writeSOF0(_image.width,_image.height);
		writeDHT();
		writeSOS();	    
	}
	
	protected function initializeEncoding () :void {
	    // Encode 8x8 macroblocks
		_bytenew=0;
		_bytepos=7;		
	}
	
	/**
	 * Encode a specified number of pixels.  Fewer pixels will be encoded if the end of the image
	 * is reached first.
	 */	
	protected function encodePixels (unitSize: int) :void
	{			    		                
	    for (var count :int = 0; !pixelsDone && count < unitSize; count++) {
		                
			RGB2YUV(_image, _xpos, _ypos);
			_DCY = processDU(YDU, fdtbl_Y, _DCY, YDC_HT, YAC_HT);
			_DCU = processDU(UDU, fdtbl_UV, _DCU, UVDC_HT, UVAC_HT);
			_DCV = processDU(VDU, fdtbl_UV, _DCV, UVDC_HT, UVAC_HT);
				
            _xpos += 8;
			
			// If we have moved past the end of the line, move to the next one.
			if (_xpos >= _image.width) {
                _xpos = 0;			
    			_ypos += 8;
    			
    			// If we have moved past the last line, we are done.
    			if (_ypos >= _image.height) {
    			    pixelsDone = true;
    			}		    
			}
		}
	}
	
	/**
	 * Add the EOI marker to the end of the buffer, and make the result available to the consumer
	 * of this class.
	 */
	protected function completeEncoding () :void
	{
		// Do the bit alignment of the EOI marker
		if ( _bytepos >= 0 ) {
			var fillbits:BitString = new BitString();
			fillbits.len = _bytepos+1;
			fillbits.val = (1<<(_bytepos+1))-1;
			writeBits(fillbits);
		}

		writeWord(0xFFD9); //EOI
		_encodedJpeg = _byteout;	    
	}
	
	/**
	 * Return true if the encoding is complete.
	 */
	public function isComplete () :Boolean
	{
	    return null != _encodedJpeg;
	}
	
	/**
	 * Work on encoding the image for a specified number of milliseconds.  Return true if there
	 * is no more processing to do.
	 */
	public function process (timeSlice :int) :Boolean
	{	
	    const endTime :int = getTimer() + timeSlice;
	    while (! pixelsDone && getTimer() < endTime) {
	        encodePixels(_pixelGranularity);
	    }
	    
	    if (pixelsDone) {
	        completeEncoding();
	        return true;
	    }
	    
	    return false;
	}

	/**
	 * Return a byte array containing the encoded jpeg.
	 */
	public function getJpeg () :ByteArray
	{
	    return _encodedJpeg;
	}
    
    /** The image to encode **/
    protected var _image :BitmapData;

    /** Byte array to contain the resuling jpg **/
    protected var _encodedJpeg :ByteArray;

    /** Byte array to contain the jpg while encoding is in progress. **/
    protected var _byteout :ByteArray = new ByteArray();

	// Used to keep track of the positon of the writer in the byte array
	protected var _bytenew:int = 0;
	protected var _bytepos:int = 7;

    // State for the pixel block encoding process
	protected var _DCY:Number=0;
	protected var _DCU:Number=0;
	protected var _DCV:Number=0;
	protected var _ypos :int = 0;
	protected var _xpos :int = 0;
	protected var pixelsDone:Boolean = false;		
	
	/** The minumum number of pixels that will be processed at a time. **/
	protected var _pixelGranularity :int;
}
}

/**
 * Helper class originally separate 
 */
class BitString
{
	public var len:int = 0;
	public var val:int = 0;
}
