PNGEncoder类用法

引用

注意：
as3中图片转换成ByteArray再由ByteArray转换成图片的过程。
其中是调用Abode官方的类 PNGEncoder来实现的。但是之前总是报错，具体如下：
var encoder:PNGEncoder = new PNGEncoder();
然后var bytes:ByteArray=encoder.encode(_bmd);
调用encode这个方法
结果报错 1061: 调用可能未定义的方法 encode (通过 static 类型 PNGEncoder 引用)。
后来我才发现，需要将var encoder:PNGEncoder = new PNGEncoder();
然后var bytes:ByteArray=encoder.encode(_bmd); 这两句改成
var bytes:ByteArray=PNGEncoder.encode(_bmd); 因为encode为静态函数。

首先为 Abode官方的类 PNGEncoder

package 
{
        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);
            }
        }
}

然后，在as3文件中调用，将图片转换成ByteArray：

package
{
import flash.events.Event;
import flash.net.URLRequest;
import flash.display.Loader;
import flash.events.IOErrorEvent;
import flash.display.Bitmap;
import flash.display.BitmapData;
import flash.display.Sprite;
import flash.display.MovieClip;
import flash.utils.ByteArray;
//import mx.utils.Base64Decoder;
public class main extends MovieClip
{
   private var imgLoader:Loader= new Loader();;
   private var arr:Array;
   private var _bmd:BitmapData;
   public function main()
   {

    imgLoader.contentLoaderInfo.addEventListener(Event.COMPLETE, onIMGComplete);
    imgLoader.contentLoaderInfo.addEventListener(IOErrorEvent.IO_ERROR, onError);
    imgLoader.load(new URLRequest("1.jpg"));

    arr=[];
   }

   private function onIMGComplete(evt:Event):void 
   {
        var _bitmap:Bitmap=evt.target.content;
         _bmd=_bitmap.bitmapData.clone();
          imgLoader.unload ();

          var bytes:ByteArray=PNGEncoder.encode(_bmd);//转化为二进制数据  
   }
   private function onError(evt:Event):void 
   {
          trace('出错了!');
   }
  
}
}

如果需要将ByteArray再转换成图片，代码如下：

package
{
import flash.events.Event;
import flash.net.URLRequest;
import flash.display.Loader;
import flash.events.IOErrorEvent;
import flash.display.Bitmap;
import flash.display.BitmapData;
import flash.display.Sprite;
import flash.display.MovieClip;
import flash.utils.ByteArray;
public class main extends MovieClip
{
   private var imgLoader:Loader= new Loader();;
   private var arr:Array;
   private var _bmd:BitmapData;
   public function main()
   {
    imgLoader.contentLoaderInfo.addEventListener(Event.COMPLETE, onIMGComplete);
    imgLoader.contentLoaderInfo.addEventListener(IOErrorEvent.IO_ERROR, onError);
    imgLoader.load(new URLRequest("1.jpg"));

    arr=[];
   }

   private function onIMGComplete(evt:Event):void 
   {
        var _bitmap:Bitmap=evt.target.content;
    _bmd=_bitmap.bitmapData.clone();
        imgLoader.unload ();    
    var bytes:ByteArray=PNGEncoder.encode(_bmd);//转化为二进制数据 
    trace(bytes[0]);
    var load:Loader=new Loader();    
    load.loadBytes(bytes);//读取ByteArray    
    load.contentLoaderInfo.addEventListener(Event.COMPLETE, complete);    
   
   }
   private function complete(event:Event):void {    
       var bitMap:Bitmap=event.target.content as Bitmap;//读取Bitmap    
       addChild(bitMap);    }
   private function onError(evt:Event):void 
   {
          trace('出错了!');
   }
  
}
}