void playPattern(int *timer, int duration) {
  *timer = *timer >= duration ? 0 : *timer+1;
  usleep(1000);

  if(*timer == 0) {
    drawRects(step-1);
    for(int i=0; i<matrix[0]; i++) {
      if(pattern[i][step-1] == 1) {
        Mix_PlayChannel(-1, samples[i], 0);
      }
    }

    step = step < matrix[1] ? step+1 : 1;

    if(setErease && step == 1) {
      for(int i=0; i<matrix[1]; i++) {
        pattern[ereaseSample-1][i] = 0;
      }
      setErease = false;
    }
  }
}