[AS3]基于PNGEncoder实现PNG图片的透明

AS3]基于PNGEncoder实现PNG图片的透明

package 
{ 
        import flash.geom.*; 
        import flash.display.*; 
        import flash.utils.*; 
        public class PNGEncoder 
        { 
 
            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; 
                    if ( !img.transparent ) { 
                        for(var j:int=0;j < img.width;j++) { 
                            p = img.getPixel(j,i); 
                            IDAT.writeUnsignedInt( 
                                uint(((p&0xFFFFFF) << 8)|0xFF)); 
                        } 
                    } else { 
                        for(var k:int=0;k < img.width;k++) { 
                            p = img.getPixel32(k,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) { 
                if (!crcTableComputed) { 
                    crcTableComputed = true; 
                    crcTable = []; 
                    for (var n:uint = 0; n < 256; n++) { 
                        var c_1:uint = n; 
                        for (var k:uint = 0; k < 8; k++) { 
                            if (c_1 & 1) { 
                                c_1 = uint(uint(0xedb88320) ^ 
                                    uint(c_1 >>> 1)); 
                            } else { 
                                c_1 = uint(c_1 >>> 1); 
                            } 
                        } 
                        crcTable[n] = c_1; 
                    } 
                } 
                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; 
                ppng.position = p; 
                var c:uint = 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); 
            } 
        } 
}