png图片里加自定义数据
有许多的应用中，图片要和数据一起使用！比较常见的做法是，加xml文件之类的表来描述！
其实可以直接把数据写在图片里！
做法很简单！我写了点代码，大家可以参考下！
https://hub004.xindong.com/yangyiqiang/AvatarTool/blob/master/src/utils/As3PngEncoder.as
原理就是把PNG数据格式中的IEND给替换成你要的数据！
上面的类库里面是把png和xml合并到一起的！要说明一点，如果图片用工具压缩的话，数据可能会掉的！一般要把图片压好，把自己的数据放进去的！
上面是写入的方法！
读出方法如下：
package utils {
import flash.display.BitmapData;
import flash.geom.Matrix;
import flash.geom.Rectangle;
import flash.utils.ByteArray;
/**
* @author yangyiqiang
*/
/*******************************
PNGDecoder
Author: Jerion
A class that decodes png byte arrays and generates a bitmapdata.
This is my first attempt at decoding images, so there are a lot of
things that are not implemented.
So far, it can only decode truecolour with alpha png images with
no interlacing, no filter, and bit depth of 8.
********************************/
public class PNGDecoder {
private const IHDR : uint = 0x49484452;
private const PLTE : uint = 0x504c5445;
private const IDAT : uint = 0x49444154;
private const IEND : uint = 0x49454e44;
private var imgWidth : uint = 0;
private var imgHeight : uint = 0;
// file info, but not used yet.
private var bitDepth : uint = 0;
private var colourType : uint = 0;
private var compressionMethod : uint = 0;
private var filterMethod : uint = 0;
private var interlaceMethod : uint = 0;
private var chunks : Array;
private var input : ByteArray;
private var output : ByteArray;
public function PNGDecoder(ba : ByteArray = null) {
chunks = new Array();
input = new ByteArray();
output = new ByteArray();
input = ba;
if(input)
{
input.position = 0;
if (!readSignature()) throw new Error("wrong signature");
}
}
public function getIendMessage(ba : ByteArray) :Object {
chunks = new Array();
input = new ByteArray();
output = new ByteArray();
input = ba;
input.position = 0;
if (!readSignature()) throw new Error("wrong signature");
getIENDChunks();
if (_IENDChunks) {
input.position = _IENDChunks.position;
var len : uint = _IENDChunks.length;
var bytes:ByteArray=new ByteArray();
bytes.writeBytes(input,input.position,len);
bytes.position=0;
return bytes.readObject();
}
return null;
}
// recieves the bytearray and returns a bitmapdata
public function decode(ba : ByteArray) : BitmapData {
chunks = new Array();
input = new ByteArray();
output = new ByteArray();
input = ba;
input.position = 0;
if (!readSignature()) throw new Error("wrong signature");
getChunks();
for (var i : int = 0; i < chunks.length; ++i) {
switch(chunks[i].type) {
case IHDR:
processIHDR(i);
break;
// case PLTE: processPLTE(i); break;
case IDAT:
processIDAT(i);
break;
// case IEND: processIEND(i); break;
}
}
// Since the image is inverted in x and y, I have to flip it using a Matrix object. There should be a better solution for this..
var bd0 : BitmapData = new BitmapData(imgWidth, imgHeight);
var bd1 : BitmapData = new BitmapData(imgWidth, imgHeight, true, 0xffffff);
if (output.length > 0 && (imgWidth * imgHeight * 4) == output.length) {
output.position = 0;
bd0.setPixels(new Rectangle(0, 0, imgWidth, imgHeight), output);
var mat : Matrix = new Matrix();
mat.scale(-1, -1);
mat.translate(imgWidth, imgHeight);
bd1.draw(bd0, mat);
}
return bd1;
}
// read the header of the image
private function processIHDR(index : uint) : void {
input.position = chunks[index].position;
imgWidth = input.readUnsignedInt();
imgHeight = input.readUnsignedInt();
// file info, but is not used yet
bitDepth = input.readUnsignedByte();
colourType = input.readUnsignedByte();
compressionMethod = input.readUnsignedByte();
filterMethod = input.readUnsignedByte();
interlaceMethod = input.readUnsignedByte();
}
// This can't handle multiple IDATs yet, and it can only decode filter 0 scanlines.
private function processIDAT(index : uint) : void {
var tmp : ByteArray = new ByteArray();
var pixw : uint = imgWidth * 4;
tmp.writeBytes(input, chunks[index].position, chunks[index].length);
tmp.uncompress();
for (var i : int = tmp.length - 1; i > 0; --i) {
if (i % (pixw + 1) != 0) {
var a : uint = tmp[i];
var b : uint = tmp[i - 1];
var g : uint = tmp[i - 2];
var r : uint = tmp[i - 3];
output.writeByte(a);
output.writeByte(r);
output.writeByte(g);
output.writeByte(b);
i -= 3;
}
}
}
private function getChunks() : void {
var pos : uint = 0;
var len : uint = 0;
var type : uint = 0;
var loopEnd : int = input.length;
while (input.position < loopEnd) {
len = input.readUnsignedInt();
type = input.readUnsignedInt();
pos = input.position;
input.position += len;
input.position += 4;
// crc block. It is ignored right now, but if you want to retrieve it, replace this line with "input.readUnsignedInt()"
chunks.push({position:pos, length:len, type:type});
}
}
private var _IENDChunks : Object;
private var _pos : uint = 0;
private var _len : uint = 0;
private var _type : uint = 0;
public function getIENDChunks() : Object {
_pos = 0;
_len = 0;
_type = 0;
var loopEnd : int = input.length;
while (input.position < loopEnd) {
_len = input.readUnsignedInt();
_type = input.readUnsignedInt();
if (_type == IEND) {
_pos = input.position;
_IENDChunks = {position:_pos, length:_len, type:_type};
return _IENDChunks;
} else {
input.position += _len;
input.position += 4;
}
}
return _IENDChunks;
}
private function readSignature() : Boolean {
return (input.readUnsignedInt() == 0x89504e47 && input.readUnsignedInt() == 0x0D0A1A0A);
}
// transform the chunk type to a string representation
private function fixType(num : uint) : String {
var ret : String = "";
var str : String = num.toString(16);
while (str.length < 8) str = "0" + str;
ret += String.fromCharCode(parseInt(str.substr(0, 2), 16));
ret += String.fromCharCode(parseInt(str.substr(2, 2), 16));
ret += String.fromCharCode(parseInt(str.substr(4, 2), 16));
ret += String.fromCharCode(parseInt(str.substr(6, 2), 16));
return ret;
}
}
}因为我这边是把数据直接writeObject了！所以只提供了个
public function getIendMessage(ba : ByteArray) :Object自己用时，可以换成你所希望的！个人认为还是用writeObject好点！解析成数据时效率会高点