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Filename : decoder.js
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/**
 * @author shaozilee
 *
 * Bmp format decoder,support 1bit 4bit 8bit 24bit bmp
 *
 */

function BmpDecoder(buffer,is_with_alpha) {
  this.pos = 0;
  this.buffer = buffer;
  this.is_with_alpha = !!is_with_alpha;
  this.bottom_up = true;
  this.flag = this.buffer.toString("utf-8", 0, this.pos += 2);
  if (this.flag != "BM") throw new Error("Invalid BMP File");
  this.parseHeader();
  this.parseRGBA();
}

BmpDecoder.prototype.parseHeader = function() {
  this.fileSize = this.buffer.readUInt32LE(this.pos);
  this.pos += 4;
  this.reserved = this.buffer.readUInt32LE(this.pos);
  this.pos += 4;
  this.offset = this.buffer.readUInt32LE(this.pos);
  this.pos += 4;
  this.headerSize = this.buffer.readUInt32LE(this.pos);
  this.pos += 4;
  this.width = this.buffer.readUInt32LE(this.pos);
  this.pos += 4;
  this.height = this.buffer.readInt32LE(this.pos);
  this.pos += 4;
  this.planes = this.buffer.readUInt16LE(this.pos);
  this.pos += 2;
  this.bitPP = this.buffer.readUInt16LE(this.pos);
  this.pos += 2;
  this.compress = this.buffer.readUInt32LE(this.pos);
  this.pos += 4;
  this.rawSize = this.buffer.readUInt32LE(this.pos);
  this.pos += 4;
  this.hr = this.buffer.readUInt32LE(this.pos);
  this.pos += 4;
  this.vr = this.buffer.readUInt32LE(this.pos);
  this.pos += 4;
  this.colors = this.buffer.readUInt32LE(this.pos);
  this.pos += 4;
  this.importantColors = this.buffer.readUInt32LE(this.pos);
  this.pos += 4;

  if(this.bitPP === 16 && this.is_with_alpha){
    this.bitPP = 15
  }
  if (this.bitPP < 15) {
    var len = this.colors === 0 ? 1 << this.bitPP : this.colors;
    this.palette = new Array(len);
    for (var i = 0; i < len; i++) {
      var blue = this.buffer.readUInt8(this.pos++);
      var green = this.buffer.readUInt8(this.pos++);
      var red = this.buffer.readUInt8(this.pos++);
      var quad = this.buffer.readUInt8(this.pos++);
      this.palette[i] = {
        red: red,
        green: green,
        blue: blue,
        quad: quad
      };
    }
  }
  if(this.height < 0) {
    this.height *= -1;
    this.bottom_up = false;
  }

}

BmpDecoder.prototype.parseRGBA = function() {
    var bitn = "bit" + this.bitPP;
    var len = this.width * this.height * 4;
    this.data = new Buffer(len);
    this[bitn]();
};

BmpDecoder.prototype.bit1 = function() {
  var xlen = Math.ceil(this.width / 8);
  var mode = xlen%4;
  var y = this.height >= 0 ? this.height - 1 : -this.height
  for (var y = this.height - 1; y >= 0; y--) {
    var line = this.bottom_up ? y : this.height - 1 - y
    for (var x = 0; x < xlen; x++) {
      var b = this.buffer.readUInt8(this.pos++);
      var location = line * this.width * 4 + x*8*4;
      for (var i = 0; i < 8; i++) {
        if(x*8+i<this.width){
          var rgb = this.palette[((b>>(7-i))&0x1)];

          this.data[location+i*4] = 0;
          this.data[location+i*4 + 1] = rgb.blue;
          this.data[location+i*4 + 2] = rgb.green;
          this.data[location+i*4 + 3] = rgb.red;

        }else{
          break;
        }
      }
    }

    if (mode != 0){
      this.pos+=(4 - mode);
    }
  }
};

BmpDecoder.prototype.bit4 = function() {
    //RLE-4
    if(this.compress == 2){
        this.data.fill(0xff);

        var location = 0;
        var lines = this.bottom_up?this.height-1:0;
        var low_nibble = false;//for all count of pixel

        while(location<this.data.length){
            var a = this.buffer.readUInt8(this.pos++);
            var b = this.buffer.readUInt8(this.pos++);
            //absolute mode
            if(a == 0){
                if(b == 0){//line end
                    if(this.bottom_up){
                        lines--;
                    }else{
                        lines++;
                    }
                    location = lines*this.width*4;
                    low_nibble = false;
                    continue;
                }else if(b == 1){//image end
                    break;
                }else if(b ==2){
                    //offset x,y
                    var x = this.buffer.readUInt8(this.pos++);
                    var y = this.buffer.readUInt8(this.pos++);
                    if(this.bottom_up){
                        lines-=y;
                    }else{
                        lines+=y;
                    }

                    location +=(y*this.width*4+x*4);
                }else{
                    var c = this.buffer.readUInt8(this.pos++);
                    for(var i=0;i<b;i++){
                        if (low_nibble) {
                            setPixelData.call(this, (c & 0x0f));
                        } else {
                            setPixelData.call(this, (c & 0xf0)>>4);
                        }

                        if ((i & 1) && (i+1 < b)){
                            c = this.buffer.readUInt8(this.pos++);
                        }

                        low_nibble = !low_nibble;
                    }

                    if ((((b+1) >> 1) & 1 ) == 1){
                        this.pos++
                    }
                }

            }else{//encoded mode
                for (var i = 0; i < a; i++) {
                    if (low_nibble) {
                        setPixelData.call(this, (b & 0x0f));
                    } else {
                        setPixelData.call(this, (b & 0xf0)>>4);
                    }
                    low_nibble = !low_nibble;
                }
            }

        }




        function setPixelData(rgbIndex){
            var rgb = this.palette[rgbIndex];
            this.data[location] = 0;
            this.data[location + 1] = rgb.blue;
            this.data[location + 2] = rgb.green;
            this.data[location + 3] = rgb.red;
            location+=4;
        }
    }else{

      var xlen = Math.ceil(this.width/2);
      var mode = xlen%4;
      for (var y = this.height - 1; y >= 0; y--) {
        var line = this.bottom_up ? y : this.height - 1 - y
        for (var x = 0; x < xlen; x++) {
          var b = this.buffer.readUInt8(this.pos++);
          var location = line * this.width * 4 + x*2*4;

          var before = b>>4;
          var after = b&0x0F;

          var rgb = this.palette[before];
          this.data[location] = 0;
          this.data[location + 1] = rgb.blue;
          this.data[location + 2] = rgb.green;
          this.data[location + 3] = rgb.red;


          if(x*2+1>=this.width)break;

          rgb = this.palette[after];

          this.data[location+4] = 0;
          this.data[location+4 + 1] = rgb.blue;
          this.data[location+4 + 2] = rgb.green;
          this.data[location+4 + 3] = rgb.red;

        }

        if (mode != 0){
          this.pos+=(4 - mode);
        }
      }

    }

};

BmpDecoder.prototype.bit8 = function() {
    //RLE-8
    if(this.compress == 1){
        this.data.fill(0xff);

        var location = 0;
        var lines = this.bottom_up?this.height-1:0;

        while(location<this.data.length){
            var a = this.buffer.readUInt8(this.pos++);
            var b = this.buffer.readUInt8(this.pos++);
            //absolute mode
            if(a == 0){
                if(b == 0){//line end
                    if(this.bottom_up){
                        lines--;
                    }else{
                        lines++;
                    }
                    location = lines*this.width*4;
                    continue;
                }else if(b == 1){//image end
                    break;
                }else if(b ==2){
                    //offset x,y
                    var x = this.buffer.readUInt8(this.pos++);
                    var y = this.buffer.readUInt8(this.pos++);
                    if(this.bottom_up){
                        lines-=y;
                    }else{
                        lines+=y;
                    }

                    location +=(y*this.width*4+x*4);
                }else{
                    for(var i=0;i<b;i++){
                        var c = this.buffer.readUInt8(this.pos++);
                        setPixelData.call(this, c);
                    }
                    if(b&1 == 1){
                        this.pos++;
                    }

                }

            }else{//encoded mode
                for (var i = 0; i < a; i++) {
                    setPixelData.call(this, b);
                }
            }

        }




        function setPixelData(rgbIndex){
            var rgb = this.palette[rgbIndex];
            this.data[location] = 0;
            this.data[location + 1] = rgb.blue;
            this.data[location + 2] = rgb.green;
            this.data[location + 3] = rgb.red;
            location+=4;
        }
    }else {
        var mode = this.width % 4;
        for (var y = this.height - 1; y >= 0; y--) {
            var line = this.bottom_up ? y : this.height - 1 - y
            for (var x = 0; x < this.width; x++) {
                var b = this.buffer.readUInt8(this.pos++);
                var location = line * this.width * 4 + x * 4;
                if (b < this.palette.length) {
                    var rgb = this.palette[b];

                    this.data[location] = 0;
                    this.data[location + 1] = rgb.blue;
                    this.data[location + 2] = rgb.green;
                    this.data[location + 3] = rgb.red;

                } else {
                    this.data[location] = 0;
                    this.data[location + 1] = 0xFF;
                    this.data[location + 2] = 0xFF;
                    this.data[location + 3] = 0xFF;
                }
            }
            if (mode != 0) {
                this.pos += (4 - mode);
            }
        }
    }
};

BmpDecoder.prototype.bit15 = function() {
  var dif_w =this.width % 3;
  var _11111 = parseInt("11111", 2),_1_5 = _11111;
  for (var y = this.height - 1; y >= 0; y--) {
    var line = this.bottom_up ? y : this.height - 1 - y
    for (var x = 0; x < this.width; x++) {

      var B = this.buffer.readUInt16LE(this.pos);
      this.pos+=2;
      var blue = (B & _1_5) / _1_5 * 255 | 0;
      var green = (B >> 5 & _1_5 ) / _1_5 * 255 | 0;
      var red = (B >> 10 & _1_5) / _1_5 * 255 | 0;
      var alpha = (B>>15)?0xFF:0x00;

      var location = line * this.width * 4 + x * 4;

      this.data[location] = alpha;
      this.data[location + 1] = blue;
      this.data[location + 2] = green;
      this.data[location + 3] = red;
    }
    //skip extra bytes
    this.pos += dif_w;
  }
};

BmpDecoder.prototype.bit16 = function() {
  var dif_w =(this.width % 2)*2;
  //default xrgb555
  this.maskRed = 0x7C00;
  this.maskGreen = 0x3E0;
  this.maskBlue =0x1F;
  this.mask0 = 0;

  if(this.compress == 3){
    this.maskRed = this.buffer.readUInt32LE(this.pos);
    this.pos+=4;
    this.maskGreen = this.buffer.readUInt32LE(this.pos);
    this.pos+=4;
    this.maskBlue = this.buffer.readUInt32LE(this.pos);
    this.pos+=4;
    this.mask0 = this.buffer.readUInt32LE(this.pos);
    this.pos+=4;
  }


  var ns=[0,0,0];
  for (var i=0;i<16;i++){
    if ((this.maskRed>>i)&0x01) ns[0]++;
    if ((this.maskGreen>>i)&0x01) ns[1]++;
    if ((this.maskBlue>>i)&0x01) ns[2]++;
  }
  ns[1]+=ns[0]; ns[2]+=ns[1];	ns[0]=8-ns[0]; ns[1]-=8; ns[2]-=8;

  for (var y = this.height - 1; y >= 0; y--) {
    var line = this.bottom_up ? y : this.height - 1 - y;
    for (var x = 0; x < this.width; x++) {

      var B = this.buffer.readUInt16LE(this.pos);
      this.pos+=2;

      var blue = (B&this.maskBlue)<<ns[0];
      var green = (B&this.maskGreen)>>ns[1];
      var red = (B&this.maskRed)>>ns[2];

      var location = line * this.width * 4 + x * 4;

      this.data[location] = 0;
      this.data[location + 1] = blue;
      this.data[location + 2] = green;
      this.data[location + 3] = red;
    }
    //skip extra bytes
    this.pos += dif_w;
  }
};

BmpDecoder.prototype.bit24 = function() {
  for (var y = this.height - 1; y >= 0; y--) {
    var line = this.bottom_up ? y : this.height - 1 - y
    for (var x = 0; x < this.width; x++) {
      //Little Endian rgb
      var blue = this.buffer.readUInt8(this.pos++);
      var green = this.buffer.readUInt8(this.pos++);
      var red = this.buffer.readUInt8(this.pos++);
      var location = line * this.width * 4 + x * 4;
      this.data[location] = 0;
      this.data[location + 1] = blue;
      this.data[location + 2] = green;
      this.data[location + 3] = red;
    }
    //skip extra bytes
    this.pos += (this.width % 4);
  }

};

/**
 * add 32bit decode func
 * @author soubok
 */
BmpDecoder.prototype.bit32 = function() {
  //BI_BITFIELDS
  if(this.compress == 3){
    this.maskRed = this.buffer.readUInt32LE(this.pos);
    this.pos+=4;
    this.maskGreen = this.buffer.readUInt32LE(this.pos);
    this.pos+=4;
    this.maskBlue = this.buffer.readUInt32LE(this.pos);
    this.pos+=4;
    this.mask0 = this.buffer.readUInt32LE(this.pos);
    this.pos+=4;
      for (var y = this.height - 1; y >= 0; y--) {
          var line = this.bottom_up ? y : this.height - 1 - y;
          for (var x = 0; x < this.width; x++) {
              //Little Endian rgba
              var alpha = this.buffer.readUInt8(this.pos++);
              var blue = this.buffer.readUInt8(this.pos++);
              var green = this.buffer.readUInt8(this.pos++);
              var red = this.buffer.readUInt8(this.pos++);
              var location = line * this.width * 4 + x * 4;
              this.data[location] = alpha;
              this.data[location + 1] = blue;
              this.data[location + 2] = green;
              this.data[location + 3] = red;
          }
      }

  }else{
      for (var y = this.height - 1; y >= 0; y--) {
          var line = this.bottom_up ? y : this.height - 1 - y;
          for (var x = 0; x < this.width; x++) {
              //Little Endian argb
              var blue = this.buffer.readUInt8(this.pos++);
              var green = this.buffer.readUInt8(this.pos++);
              var red = this.buffer.readUInt8(this.pos++);
              var alpha = this.buffer.readUInt8(this.pos++);
              var location = line * this.width * 4 + x * 4;
              this.data[location] = alpha;
              this.data[location + 1] = blue;
              this.data[location + 2] = green;
              this.data[location + 3] = red;
          }
      }

  }




};

BmpDecoder.prototype.getData = function() {
  return this.data;
};

module.exports = function(bmpData) {
  var decoder = new BmpDecoder(bmpData);
  return decoder;
};