slantMello glitch scrolling bars for RGB Shades code

effects.h

// Draw slanting bars scrolling across the array
void slantMello() {

  static byte slantPos = 0;
  static byte distortDelay;
  static byte changeDelay = 10;
  static byte lastoffset = 1;
  static uint16_t slowcolor = 0;

  // startup tasks
  if (effectInit == false) {
    effectInit = true;
    effectDelay = 5;
    distortDelay = 10;
    selectRandomPalette();
  }

  // pseudorandom seed
  uint8_t ry = lastoffset;
  uint8_t posoffset;
  ry ^= (ry << 7);
  ry ^= (ry >> 5);
  ry ^= (ry << 3);

  if (--distortDelay < 1) {
    distortDelay = random(5,40);
    lastoffset = ry;
    if (--changeDelay < 1) {
      changeDelay = random8(100,255);
      selectRandomPalette();
    }
  }

  for (byte y = 0; y < kMatrixHeight; y++) {

    // pseudorandom offset
    ry ^= (ry << 7);
    ry ^= (ry >> 5);
    ry ^= (ry << 3);
    posoffset = ry / 4;
    
    for (byte x = 0; x < kMatrixWidth; x++) {
      byte pcolor = cubicwave8(x * 32 + y * 32 + slantPos + (posoffset-64));
      leds[XY(x, y)] = ColorFromPalette(currentPalette, pcolor/4+slowcolor/64, pcolor*(pcolor > 16));
    }
  }
  slowcolor+=4;
  slantPos -= 1;

}