ArrayList<Seg> segs = new ArrayList<Seg>();

void setup(){
  size(500,500);
  frameRate(20);
 
}
boolean isRed = true;
int offset;

color RED = color(200,0,0);
color WHITE = color(255);

boolean metatoggle = true;

void draw(){
  background(0,0,100);
  //translate(0,offset*3);
  strokeWeight(5);
  isRed = true;
  stroke(RED);
  int i = offset;  
    if(offset % 8 == 0 ){
       metatoggle = !metatoggle;
    } 

  if(!metatoggle){
     togglePen(); 
}
  
    for(Seg s : segs){
    if(i % 8 == 0 && !(offset == i)){
       togglePen(); 
    }
    s.draw();
    i--;
  }  
  offset--;
  
}

void togglePen(){
  isRed = ! isRed;
  if(isRed){
    stroke(RED);
  } else {
     stroke(WHITE); 
  }
}


void keyPressed(){
if(key == ' '){ reset();}
    
}

void reset(){
segs = new ArrayList<Seg>();
 
}

void mouseDragged(){
  segs.add(new Seg(pmouseX,pmouseY,mouseX,mouseY));
}


class Seg{
  float e1x,e1y,e2x,e2y;
  Seg(float x1, float y1, float x2, float y2){
     e1x = x1; e1y = y1;
     e2x = x2; e2y = y2; 
  }
  void draw(){
     line(e1x,e1y,e2x,e2y); 
  }
}