Hello,

i am not sure if what i did here is wrong or good, but i got some boxes to display :)
the slider controls the zoom.

the main problem i think was that your particule.draw() never gets called. i fixed that in the code below. (look in the main draw method.)

i hope this helps !

Happy Xmas !

hri

1. 
   import guicomponents.*;
   import processing.opengl.*;
   
   //declare
   GVertSlider sdrScale;
   float zoom;
   float zoomfactor;
   //class array and integer
   Particle p[];
   int num;
   
   
   void setup(){
     size(500,500,OPENGL);
     smooth();
     fill(000);
     frameRate(30);
     rectMode(CENTER);
    
     GComponent.globalColor = GCScheme.getColor(this,  GCScheme.GREEN_SCHEME);
     GComponent.globalFont = GFont.getFont(this, "Serif", 11);
     sdrScale = new GVertSlider(this, 0, 0, 10, height);
     sdrScale.setLimits(200, 0, height);
     sdrScale.setInertia(1);
    
     zoomfactor = 45.0f / height;
     zoom = 0.1 * zoomfactor * sdrScale.getValue();  
      initialize();
   }
   
   void draw(){
    
       pushMatrix();
     
       translate(width/2, height/2, -200);
       noStroke();
       background(000);
       lights();
     
     
       scale(zoom);
       rotateX(frameCount*PI/150);
       rotateY(frameCount*PI/170);
       rotateZ(frameCount*PI/90);
         
       fill(255);
       stroke(255);
       line(-100, 0, 0, 100, 0, 0);
       line(0, -100, 0, 0, 100, 0);
       line(0, 0, -100, 0, 0, 100);
      
    
     
      for(int i=0;i<p.length;i++){
        p[i].update();
        p[i].draw();
      }
      popMatrix();
   }
   void initialize() {  
       num=int(random(2,20));
       p=new Particle[num];
       for(int i=0; i<num; i++) {
         p[i]=new Particle();
       }
   }
   
   void handleSliderEvents(GSlider slider){
     zoom = zoomfactor * slider.getValue() * 0.1f;
   }
   
   
   //Particle class
   class Particle{
    float f;
    float x,y,rad,gray;
    float dir,dirD,speed;
     Particle(){
       f=random(2,10);
       x=random(width);   
       y=random(height);   
       rad=random(3,15);   
      
       gray=random(100,255);   
       dir=random(360); // a random direction in angles.
       dirD=random(-2,2); // a random direction in angles.
       speed=random(1.5,4);         
     }
    
     //this method could handle the movement of your particule.
     void update(){
    
     }
     void draw(){
     
       box(90);
          fill(255);
       stroke(255);
       line(-100, 0, 0, 100, 0, 0);
       line(0, -100, 0, 0, 100, 0);
       line(0, 0, -100, 0, 0, 100);
       translate(f*10,f*10);
     }
   }