AS3 写png图片编码器

关于AS3的png图片编码器：
代码如下：

1. /*
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15. derived from the source code without prior written permission.
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34. */
35. package com.adobe .images
36. {
37. import flash.geom .*;
38. import flash.display .Bitmap ;
39. import flash.display .BitmapData ;
40. import flash.utils .ByteArray ;
41.  
42. public class PNGEncoder
43. {
44.     public static function encode( img:BitmapData) :ByteArray {
45.         // Create output byte array
46.         var png:ByteArray = new ByteArray( ) ;
47.         // Write PNG signature
48.         png.writeUnsignedInt ( 0x89504e47) ;
49.         png.writeUnsignedInt ( 0x0D0A1A0A) ;
50.         // Build IHDR chunk
51.         var IHDR:ByteArray = new ByteArray( ) ;
52.         IHDR.writeInt ( img.width ) ;
53.         IHDR.writeInt ( img.height ) ;
54.         IHDR.writeUnsignedInt ( 0x08060000) ; // 32bit RGBA
55.         IHDR.writeByte ( 0 ) ;
56.         writeChunk( png,0x49484452,IHDR) ;
57.         // Build IDAT chunk
58.         var IDAT:ByteArray= new ByteArray( ) ;
59.         for ( var i:int =0 ;i < img.height ;i++) {
60.             // no filter
61.             IDAT.writeByte ( 0 ) ;
62.             var p:uint;
63.             var j:int ;
64.             if ( !img.transparent ) {
65.                 for ( j=0 ;j < img.width ;j++) {
66.                     p = img.getPixel ( j,i) ;
67.                     IDAT.writeUnsignedInt (
68.                         uint( ( ( p&0xFFFFFF) << 8 ) |0xFF) ) ;
69.                 }
70.             } else {
71.                 for ( j=0 ;j < img.width ;j++) {
72.                     p = img.getPixel32 ( j,i) ;
73.                     IDAT.writeUnsignedInt (
74.                         uint( ( ( p&0xFFFFFF) << 8 ) |
75.                         ( p>>>24 ) ) ) ;
76.                 }
77.             }
78.         }
79.         IDAT.compress ( ) ;
80.         writeChunk( png,0x49444154,IDAT) ;
81.         // Build IEND chunk
82.         writeChunk( png,0x49454E44,null ) ;
83.         // return PNG
84.         return png;
85.     }
86.  
87.     private static var crcTable:Array ;
88.     private static var crcTableComputed:Boolean = false ;
89.  
90.     private static function writeChunk( png:ByteArray,
91.             type :uint, data :ByteArray) :void {
92.         if ( !crcTableComputed) {
93.             crcTableComputed = true ;
94.             crcTable = [ ] ;
95.             var c:uint;
96.             for ( var n:uint = 0 ; n < 256 ; n++) {
97.                 c = n;
98.                 for ( var k:uint = 0 ; k < 8 ; k++) {
99.                     if ( c & 1 ) {
100.                         c = uint( uint( 0xedb88320) ^
101.                             uint( c >>> 1 ) ) ;
102.                     } else {
103.                         c = uint( c >>> 1 ) ;
104.                     }
105.                 }
106.                 crcTable[ n] = c;
107.             }
108.         }
109.         var len:uint = 0 ;
110.         if ( data != null ) {
111.             len = data .length ;
112.         }
113.         png.writeUnsignedInt ( len) ;
114.         var p:uint = png.position ;
115.         png.writeUnsignedInt ( type ) ;
116.         if ( data != null ) {
117.             png.writeBytes ( data ) ;
118.         }
119.         var e :uint = png.position ;
120.         png.position = p;
121.         c = 0xffffffff;
122.         for ( var i:int = 0 ; i < ( e-p) ; i++) {
123.             c = uint( crcTable[
124.                 ( c ^ png.readUnsignedByte ( ) ) &
125.                 uint( 0xff) ] ^ uint( c >>> 8 ) ) ;
126.         }
127.         c = uint( c^uint( 0xffffffff) ) ;
128.         png.position = e ;
129.         png.writeUnsignedInt ( c) ;
130.     }
131. }
132. }

如何使用：

Flex Paint (需要Flash 9)

１、如图设置界面；
２、定义一个BitmapData 对象
　　　var bd:BitmapData = new BitmapData(canvas.width,canvas.height);　
３、将canvas中的像素拷贝到这个对象里
　　　bd.draw(canvas);
４、然后将BitmapData 转换成png格式的ByteArray 对象
５、将最后的png二进制传到服务器端保存．

来自:http://www.cnblogs.com/FireYang/archive/2007/02/10/646839.html