Particle[] p;
Force gravity;
float friction;
float restitution;
boolean SAVING;
int saveLag;
framePoster fPost = new framePoster("verletchain","verletchain");
void setup(){
  size(600,600);
  background(255);
  p = new Particle[40];
  for(int i=0;i<40;i++){
    p[i]=new Particle(10.0f+6.0f*i,600.0f,10.0f+6.0f*i,600.0f);
  }
  gravity = new Force(0.0f,0.0f);
  friction=0.1f;
  restitution=1.0f;
  fill(0);
  rect(0,0,600,600);
  fill(255);
  rect(4,4,592,592);

  noFill();
  for(int c=0;c<40;c++){
    for(int i=1;i<40;i++){
      p[i].update(gravity,friction);
    }
    for(int r=0;r<1;r++){
      fixlengthpivot(p[0],p[1],10.0f);
      for(int i=1;i<39;i++){
        p[i].constrain(0.0f,600.0f,restitution);
        fixlength(p[i],p[i+1],10.0f);
      }
    }
  }
  SAVING=false;
  saveLag=10;

}



void draw(){

  for(int c=0;c<10;c++){
    noStroke();
    fill(200,0,0,20);
    if(random(1.0f)<0.1f) ellipse(p[0].x, p[0].y,8,8);
    for(int i=0;i<39;i++){
      stroke(max(0,200-i*40),0,0,10);
      line(p[i].x, p[i].y,p[i+1].x, p[i+1].y);
    }

    for(int i=1;i<40;i++){
      p[i].update(gravity,friction);
    }
    for(int r=0;r<4;r++){
      fixlengthpivot(p[0],p[1],10.0f);
      for(int i=1;i<39;i++){
        p[i].constrain(0.0f,600.0f,restitution);
        fixlength(p[i],p[i+1],10.0f);
      }
    }  
  }
  if(SAVING) saveLag--;
  if(saveLag<=0){
    SAVING=false;
    saveLag=10;
  }

}

void fixlength(Particle a, Particle b, float l){
  float d1 = dist(a.x,a.y,b.x,b.y);
  float d2 = 0.5*(d1-l)/d1;
  float dx=(b.x-a.x)*d2; 
  float dy=(b.y-a.y)*d2;
  a.x+=dx;
  a.y+=dy;
  b.x-=dx;
  b.y-=dy;


}

void fixlengthpivot(Particle a, Particle b, float l){
  float d1 = dist(a.x,a.y,b.x,b.y);
  float d2 = (d1-l)/d1;
  float dx=(b.x-a.x)*d2; 
  float dy=(b.y-a.y)*d2;
  b.x-=dx;
  b.y-=dy;
}

void mouseDragged(){
  int mx=constrain(mouseX,0,600);
  int my=constrain(mouseY,0,6000);

  for(int i=0;i<40;i++){
    p[i].x += mx - p[0].x;
    p[i].y += my - p[0].y;
  }

}

void keyPressed(){
  if(key==' '){
    filter(BLUR,1); 
    fill(255,20);
    rect(4,4,592,592); 
  }
  else if (((key == 's')||(key == 'S'))&&(!SAVING)) {      
    SAVING=true;
    fPost.postFrame();   
  }
  else{

    fill(0);
    rect(0,0,600,600);
    fill(255);
    rect(4,4,592,592);  
    for(int i=0;i<40;i++){
      p[i]=new Particle(10.0f+6.0f*i,600.0f,10.0f+6.0f*i,600.0f);
    }
    for(int c=0;c<40;c++){
      for(int i=1;i<40;i++){
        p[i].update(gravity,friction);
      }
      for(int r=0;r<1;r++){
        fixlengthpivot(p[0],p[1],10.0f);
        for(int i=1;i<39;i++){
          p[i].constrain(0.0f,600.0f,restitution);
          fixlength(p[i],p[i+1],10.0f);
        }
      }
    }
  }

}