关于AS3的png图片编码器：
代码如下：

1. /*
2. Adobe Systems Incorporated(r) Source Code License Agreement
3. Copyright(c) 2005 Adobe Systems Incorporated. All rights reserved.
5. Please read this Source Code License Agreement carefully before using
6. the source code.
8. Adobe Systems Incorporated grants to you a perpetual, worldwide, non-exclusive,
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15. derived from the source code without prior written permission.
17. You agree to indemnify, hold harmless and defend Adobe Systems Incorporated from and
18. against any loss, damage, claims or lawsuits, including attorney's
19. fees that arise or result from your use or distribution of the source
20. code.
22. THIS SOURCE CODE IS PROVIDED "AS IS" AND "WITH ALL FAULTS", WITHOUT
23. ANY TECHNICAL SUPPORT OR ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING,
24. BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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26. NON-INFRINGEMENT, TITLE OR QUIET ENJOYMENT.  IN NO EVENT SHALL MACROMEDIA
27. OR ITS SUPPLIERS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
28. EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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32. OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOURCE CODE, EVEN IF
33. ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.     }
87.     private static var crcTable:Array;
88.     private static var crcTableComputed:Boolean = false;
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．

原文:

Global Variables within Flex Applications

在Flex应用程序中的全局变量

最近在Flex Components的邮件列表里经常有这样的一些提问：如果在Flex应用程序中设置全局变量？由于它的经常出现，所以在我的blog上（当然是指原文的作者）贴出答案。
其实非常简单，只用在你的主应用程序类里（mx:Application ）定义一个公有（public）的变量就可以了，如下：

你能在应用程序的任何地方访问到这个变量，像这样：
如果有需要，你也可以设置一个绑定变量。（添加一个bindable标签）
欢迎在回复里提出问题或意见。（无论是原文还是我的blog）