PSystem ps;

int num_x = 8;
int num_y = 8;
float grv = 0.8;

HScrollbar myscrollbar;
Particle[][] myparticle;

void setup() {
  size(800, 500);

  myscrollbar = new HScrollbar(0, 20, width/2, 10, 3*5+1);

  ps = (PSystem)loadPlugin("PSystem");

  ps.setGravity(grv); 
  ps.defaultSpringRestLength = 5;
  ps.defaultSpringStrength = 0.1;

  myparticle = new Particle[num_x][num_y];
  for (int i=0; i<num_y; i++) {
    for (int j=0; j<num_y; j++) {
      myparticle[i][j] = new Particle();  
      ps.addParticle(myparticle[i][j]);
      myparticle[i][j].setPos(100+50*i, 100+50*j, 0);
      if(i>0) {
        ps.addSpring(myparticle[i][j], myparticle[i-1][j]); }
      if(j>0) {
        ps.addSpring(myparticle[i][j], myparticle[i][j-1]); }
    }
  }

  // default positions for mesh corners
  myparticle[0][0].setPos(50,200,0);
  myparticle[0][num_x-1].setPos(width-50,200,0);
  myparticle[num_y-1][0].setPos(100,220,100);
  myparticle[num_y-1][num_x-1].setPos(width-100,220,100); 
  
  myparticle[0][0].fix();
  myparticle[0][num_x-1].fix();
  myparticle[num_y-1][0].fix();
  myparticle[num_y-1][num_x-1].fix();

}

void loop() {
  background(200,220,200);

  if(keyPressed) {
    if(key == 'g') {
      // flip gravity forces upside down
      grv *= -1;
      ps.setGravity(grv); }
    if(mousePressed) {
      if(key == '1')
        myparticle[0][0].setPos(mouseX,mouseY,0);
      else if(key == '2')
        myparticle[num_y-1][0].setPos(mouseX,mouseY,100);
      else if(key == '3')
        myparticle[0][num_x-1].setPos(mouseX,mouseY,0);
      else if(key == '4')
        myparticle[num_y-1][num_x-1].setPos(mouseX,mouseY,100);
      else if(key == 'f')
        myparticle[4][4].setPos(mouseX,mouseY,50);
    }
  }    

  ps.drag = myscrollbar.getPos()/2000;  
            
  myscrollbar.update();
  myscrollbar.draw();

  fill(255,255,255);  
  ps.draw();
}

// NEW CLASS FOR SCROLLBAR COPIED FROM EXAMPLE
class HScrollbar 
{ 
  int swidth, sheight;    // width and height of bar 
  int xpos, ypos;         // x and y position of bar 
  float spos, newspos;    // x position of slider 
  int sposMin, sposMax;   // max and min values of slider 
  int loose;              // how loose/heavy 
  boolean over;           // is the mouse over the slider? 
  boolean locked; 
  float ratio; 
 
  HScrollbar (int xp, int yp, int sw, int sh, int l) { 
    swidth = sw; 
    sheight = sh; 
    int widthtoheight = sw - sh; 
    ratio = (float)sw / (float)widthtoheight; 
    xpos = xp; 
    ypos = yp-sheight/2; 
    spos = xpos + swidth/2 - sheight/2; 
    newspos = spos; 
    sposMin = xpos; 
    sposMax = xpos + swidth - sheight; 
    loose = l; 
  } 
 
  void update() { 
    if(over()) { 
      over = true; 
    } else { 
      over = false; 
    } 
    if(mousePressed && over) { 
      locked = true; 
    } 
    if(!mousePressed) { 
      locked = false; 
    } 
    if(locked) { 
      newspos = constrain(mouseX-sheight/2, sposMin, sposMax); 
    } 
    if(abs(newspos - spos) > 1) { 
      spos = spos + (newspos-spos)/loose; 
    } 
  } 
 
  int constrain(int val, int minv, int maxv) { 
    return min(max(val, minv), maxv); 
  } 
 
  boolean over() { 
    if(mouseX > xpos && mouseX < xpos+swidth && 
    mouseY > ypos && mouseY < ypos+sheight) { 
      return true; 
    } else { 
      return false; 
    } 
  } 
 
  void draw() { 
    fill(255); 
    rect(xpos, ypos, swidth, sheight); 
    if(over || locked) { 
      fill(200, 0, 0);    // color while active
    } else { 
      fill(220, 220, 220);  // color while inactive
    } 
    rect(spos, ypos, sheight, sheight); 
  } 
 
  float getPos() { 
    // convert spos to be values between 
    // 0 and the total width of the scrollbar 
    return spos * ratio; 
  } 
}