"sinelon" with no visual gaps at any speed or pixel count

sinelon.ino

// Updated sinelon (no visual gaps)
void sinelon()
{
  // a colored dot sweeping 
  // back and forth, with 
  // fading trails
  fadeToBlackBy( leds, NUM_LEDS, 20);
  int pos = beatsin16(13,0,NUM_LEDS);
  static int prevpos = 0;
  if( pos < prevpos ) { 
    fill_solid( leds+pos, (prevpos-pos)+1, CHSV(gHue,220,255));
  } else { 
    fill_solid( leds+prevpos, (pos-prevpos)+1, CHSV( gHue,220,255));
  }
  prevpos = pos;
}