decodePixel method

Implementation

void decodePixel(
    InputBuffer input, void Function(num r, num g, num b, num a) pixel) {
  if (palette != null) {
    if (bitsPerPixel == 1) {
      final bi = input.readByte();
      for (var i = 7; i >= 0; --i) {
        final b = (bi >> i) & 0x1;
        pixel(b, 0, 0, 0);
      }
      return;
    } else if (bitsPerPixel == 2) {
      final bi = input.readByte();
      for (var i = 6; i >= 0; i -= 2) {
        final b = (bi >> i) & 0x2;
        pixel(b, 0, 0, 0);
      }
    } else if (bitsPerPixel == 4) {
      final bi = input.readByte();
      final b1 = (bi >> 4) & 0xf;
      pixel(b1, 0, 0, 0);
      final b2 = bi & 0xf;
      pixel(b2, 0, 0, 0);
      return;
    } else if (bitsPerPixel == 8) {
      final b = input.readByte();
      pixel(b, 0, 0, 0);
      return;
    }
  }

  if (compression == BmpCompression.bitfields && bitsPerPixel == 32) {
    final p = input.readUint32();
    final r = (((p & redMask) >> _redShift) * _redScale).toInt();
    final g = (((p & greenMask) >> _greenShift) * _greenScale).toInt();
    final b = (((p & blueMask) >> _blueShift) * _blueScale).toInt();
    final a = ignoreAlphaChannel
        ? 255
        : (((p & alphaMask) >> _alphaShift) * _alphaScale).toInt();
    return pixel(r, g, b, a);
  } else if (bitsPerPixel == 32 && compression == BmpCompression.none) {
    final b = input.readByte();
    final g = input.readByte();
    final r = input.readByte();
    final a = input.readByte();
    return pixel(r, g, b, ignoreAlphaChannel ? 255 : a);
  } else if (bitsPerPixel == 24) {
    final b = input.readByte();
    final g = input.readByte();
    final r = input.readByte();
    return pixel(r, g, b, 255);
  } else if (bitsPerPixel == 16) {
    final p = input.readUint16();
    final r = (((p & redMask) >> _redShift) * _redScale).toInt();
    final g = (((p & greenMask) >> _greenShift) * _greenScale).toInt();
    final b = (((p & blueMask) >> _blueShift) * _blueScale).toInt();
    final a = ignoreAlphaChannel
        ? 255
        : (((p & alphaMask) >> _alphaShift) * _alphaScale).toInt();
    return pixel(r, g, b, a);
  } else {
    throw ImageException('Unsupported bitsPerPixel ($bitsPerPixel) or'
        ' compression ($compression).');
  }
}