For the PNG specification, see http://www.w3.org/TR/PNG/
. * * @langversion 3.0 * @playerversion Flash 9 * @playerversion AIR 1.1 * @productversion Flex 3 */ public class PNGEncoder implements IImageEncoder { include "../../core/Version.as"; //-------------------------------------------------------------------------- // // Class constants // //-------------------------------------------------------------------------- /** * @private * The MIME type for a PNG image. */ private static const CONTENT_TYPE:String = "image/png"; //-------------------------------------------------------------------------- // // Constructor // //-------------------------------------------------------------------------- /** * Constructor. * * @langversion 3.0 * @playerversion Flash 9 * @playerversion AIR 1.1 * @productversion Flex 3 */ public function PNGEncoder() { super(); initializeCRCTable(); } //-------------------------------------------------------------------------- // // Variables // //-------------------------------------------------------------------------- /** * @private * Used for computing the cyclic redundancy checksum * at the end of each chunk. */ private var crcTable:Array; //-------------------------------------------------------------------------- // // Properties // //-------------------------------------------------------------------------- //---------------------------------- // contentType //---------------------------------- /** * The MIME type for the PNG encoded image. * The value is"image/png".
*
* @langversion 3.0
* @playerversion Flash 9
* @playerversion AIR 1.1
* @productversion Flex 3
*/
public function get contentType():String
{
return CONTENT_TYPE;
}
//--------------------------------------------------------------------------
//
// Methods
//
//--------------------------------------------------------------------------
/**
* Converts the pixels of a BitmapData object
* to a PNG-encoded ByteArray object.
*
* @param bitmapData The input BitmapData object.
*
* @return Returns a ByteArray object containing PNG-encoded image data.
*
* @langversion 3.0
* @playerversion Flash 9
* @playerversion AIR 1.1
* @productversion Flex 3
*/
public function encode(bitmapData:BitmapData):ByteArray
{
return internalEncode(bitmapData, bitmapData.width, bitmapData.height,
bitmapData.transparent);
}
/**
* Converts a ByteArray object containing raw pixels
* in 32-bit ARGB (Alpha, Red, Green, Blue) format
* to a new PNG-encoded ByteArray object.
* The original ByteArray is left unchanged.
*
* @param byteArray The input ByteArray object containing raw pixels.
* This ByteArray should contain
* 4 * width * height bytes.
* Each pixel is represented by 4 bytes, in the order ARGB.
* The first four bytes represent the top-left pixel of the image.
* The next four bytes represent the pixel to its right, etc.
* Each row follows the previous one without any padding.
*
* @param width The width of the input image, in pixels.
*
* @param height The height of the input image, in pixels.
*
* @param transparent If false, alpha channel information
* is ignored but you still must represent each pixel
* as four bytes in ARGB format.
*
* @return Returns a ByteArray object containing PNG-encoded image data.
*
* @langversion 3.0
* @playerversion Flash 9
* @playerversion AIR 1.1
* @productversion Flex 3
*/
public function encodeByteArray(byteArray:ByteArray, width:int, height:int,
transparent:Boolean = true):ByteArray
{
return internalEncode(byteArray, width, height, transparent);
}
/**
* @private
*/
private function initializeCRCTable():void
{
crcTable = [];
for (var n:uint = 0; n < 256; n++)
{
var c:uint = 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;
}
}
/**
* @private
*/
private function internalEncode(source:Object, width:int, height:int,
transparent:Boolean = true):ByteArray
{
// The source is either a BitmapData or a ByteArray.
var sourceBitmapData:BitmapData = source as BitmapData;
var sourceByteArray:ByteArray = source as ByteArray;
if (sourceByteArray)
sourceByteArray.position = 0;
// 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(width);
IHDR.writeInt(height);
IHDR.writeByte(8); // bit depth per channel
IHDR.writeByte(6); // color type: RGBA
IHDR.writeByte(0); // compression method
IHDR.writeByte(0); // filter method
IHDR.writeByte(0); // interlace method
writeChunk(png, 0x49484452, IHDR);
// Build IDAT chunk
var IDAT:ByteArray = new ByteArray();
for (var y:int = 0; y < height; y++)
{
IDAT.writeByte(0); // no filter
var x:int;
var pixel:uint;
if (!transparent)
{
for (x = 0; x < width; x++)
{
if (sourceBitmapData)
pixel = sourceBitmapData.getPixel(x, y);
else
pixel = sourceByteArray.readUnsignedInt();
IDAT.writeUnsignedInt(uint(((pixel & 0xFFFFFF) << 8) | 0xFF));
}
}
else
{
for (x = 0; x < width; x++)
{
if (sourceBitmapData)
pixel = sourceBitmapData.getPixel32(x, y);
else
pixel = sourceByteArray.readUnsignedInt();
IDAT.writeUnsignedInt(uint(((pixel & 0xFFFFFF) << 8) |
(pixel >>> 24)));
}
}
}
IDAT.compress();
writeChunk(png, 0x49444154, IDAT);
// Build IEND chunk
writeChunk(png, 0x49454E44, null);
// return PNG
png.position = 0;
return png;
}
/**
* @private
*/
private function writeChunk(png:ByteArray, type:uint, data:ByteArray):void
{
// Write length of data.
var len:uint = 0;
if (data)
len = data.length;
png.writeUnsignedInt(len);
// Write chunk type.
var typePos:uint = png.position;
png.writeUnsignedInt(type);
// Write data.
if (data)
png.writeBytes(data);
// Write CRC of chunk type and data.
var crcPos:uint = png.position;
png.position = typePos;
var crc:uint = 0xFFFFFFFF;
for (var i:uint = typePos; i < crcPos; i++)
{
crc = uint(crcTable[(crc ^ png.readUnsignedByte()) & uint(0xFF)] ^
uint(crc >>> 8));
}
crc = uint(crc ^ uint(0xFFFFFFFF));
png.position = crcPos;
png.writeUnsignedInt(crc);
}
}
}