source: code/Website/open-flash-chart/com/adobe/images/PNGEncoder.as@ 7849

/*
        Adobe Systems Incorporated(r) Source Code License Agreement
        Copyright(c) 2005 Adobe Systems Incorporated. All rights reserved.
        
        Please read this Source Code License Agreement carefully before using
        the source code.
        
        Adobe Systems Incorporated grants to you a perpetual, worldwide, non-exclusive, 
        no-charge, royalty-free, irrevocable copyright license, to reproduce,
        prepare derivative works of, publicly display, publicly perform, and
        distribute this source code and such derivative works in source or 
        object code form without any attribution requirements.  
        
        The name "Adobe Systems Incorporated" must not be used to endorse or promote products
        derived from the source code without prior written permission.
        
        You agree to indemnify, hold harmless and defend Adobe Systems Incorporated from and
        against any loss, damage, claims or lawsuits, including attorney's 
        fees that arise or result from your use or distribution of the source 
        code.
        
        THIS SOURCE CODE IS PROVIDED "AS IS" AND "WITH ALL FAULTS", WITHOUT 
        ANY TECHNICAL SUPPORT OR ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING,
        BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
        FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  ALSO, THERE IS NO WARRANTY OF 
        NON-INFRINGEMENT, TITLE OR QUIET ENJOYMENT.  IN NO EVENT SHALL MACROMEDIA
        OR ITS SUPPLIERS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
        EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, 
        PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
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        WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR 
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*/
package com.adobe.images
{
        import flash.geom.*;
        import flash.display.Bitmap;
        import flash.display.BitmapData;
        import flash.utils.ByteArray;

        /**
         * Class that converts BitmapData into a valid PNG
         */     
        public class PNGEncoder
        {
                /**
                 * Created a PNG image from the specified BitmapData
                 *
                 * @param image The BitmapData that will be converted into the PNG format.
                 * @return a ByteArray representing the PNG encoded image data.
                 * @langversion ActionScript 3.0
                 * @playerversion Flash 9.0
                 * @tiptext
                 */                     
            public static function encode(img:BitmapData):ByteArray {
                // Create output byte array
                var png:ByteArray = new ByteArray();
                // Write PNG signature
                png.writeUnsignedInt(0x89504e47);
                png.writeUnsignedInt(0x0D0A1A0A);
                // Build IHDR chunk
                var IHDR:ByteArray = new ByteArray();
                IHDR.writeInt(img.width);
                IHDR.writeInt(img.height);
                IHDR.writeUnsignedInt(0x08060000); // 32bit RGBA
                IHDR.writeByte(0);
                writeChunk(png,0x49484452,IHDR);
                // Build IDAT chunk
                var IDAT:ByteArray= new ByteArray();
                for(var i:int=0;i < img.height;i++) {
                    // no filter
                    IDAT.writeByte(0);
                    var p:uint;
                    var j:int;
                    if ( !img.transparent ) {
                        for(j=0;j < img.width;j++) {
                            p = img.getPixel(j,i);
                            IDAT.writeUnsignedInt(
                                uint(((p&0xFFFFFF) << 8)|0xFF));
                        }
                    } else {
                        for(j=0;j < img.width;j++) {
                            p = img.getPixel32(j,i);
                            IDAT.writeUnsignedInt(
                                uint(((p&0xFFFFFF) << 8)|
                                (p>>>24)));
                        }
                    }
                }
                IDAT.compress();
                writeChunk(png,0x49444154,IDAT);
                // Build IEND chunk
                writeChunk(png,0x49454E44,null);
                // return PNG
                return png;
            }
        
            private static var crcTable:Array;
            private static var crcTableComputed:Boolean = false;
        
            private static function writeChunk(png:ByteArray, 
                    type:uint, data:ByteArray):void {
                if (!crcTableComputed) {
                    crcTableComputed = true;
                    crcTable = [];
                    var c:uint;
                    for (var n:uint = 0; n < 256; n++) {
                        c = n;
                        for (var k:uint = 0; k < 8; k++) {
                            if (c & 1) {
                                c = uint(uint(0xedb88320) ^ 
                                    uint(c >>> 1));
                            } else {
                                c = uint(c >>> 1);
                            }
                        }
                        crcTable[n] = c;
                    }
                }
                var len:uint = 0;
                if (data != null) {
                    len = data.length;
                }
                png.writeUnsignedInt(len);
                var p:uint = png.position;
                png.writeUnsignedInt(type);
                if ( data != null ) {
                    png.writeBytes(data);
                }
                var e:uint = png.position;
                png.position = p;
                c = 0xffffffff;
                for (var i:int = 0; i < (e-p); i++) {
                    c = uint(crcTable[
                        (c ^ png.readUnsignedByte()) & 
                        uint(0xff)] ^ uint(c >>> 8));
                }
                c = uint(c^uint(0xffffffff));
                png.position = e;
                png.writeUnsignedInt(c);
            }
        }
}