hi, I have this problem, where I want mouse to draw in 3D so the 3D CUBE GRID needs to be freely rotated on the screen. That is all fine. But now how do I make the objects "stick" to their places since background() is refreshing the position every frame? Some one suggested arrays, but i can't figure out how to do it.

import processing.opengl.*;

Ball b1 = new Ball();
float xpos,ypos,zpos, sz;
PGraphics bf;
float expo = 1;
float rotx, roty;
float rate = 0.01;
color c2 = color(0);

void mouseDragged()
{
rotx = rotx + (mouseY - pmouseY) * rate;
roty = roty + (mouseX - pmouseX) * rate;
}

void setup()
{
size(700,400,OPENGL);
bf = createGraphics(width,height,P3D);
stroke(150);
}

void draw()
{
background(255);

if (keyPressed && keyCode==UP)
{
  expo = expo + 0.01;
}
if (keyPressed && keyCode==DOWN)
{
  expo = expo - 0.01;
}
bf.beginDraw();
bf.background(0);
translate(350,200,0);
bf.translate(350,200,0);
rotateX(rotx);
bf.rotateX(rotx);
rotateY(roty);
bf.rotateY(roty);
scale(expo);
bf.scale(expo);
translate(-350,-350,-350);
bf.translate(-350,-350,-350);
for (int x = 150; x<=550; x+=100)
{
  for (int y = 150; y<=550; y+=100)
  {
    for (int z = 150; z<=550; z+=100)
    {      
      line(150,y,z,x,y,z);
      line(x,150,z,x,y,z);
      line(x,y,150,x,y,z);
      bf.pushMatrix();
      bf.translate(x,y,z);
      bf.noStroke();
      bf.fill(x/10,y/10,z/10);
      bf.rectMode(CENTER);
      bf.rect(0,0,10,10);
      bf.rotateX(PI/2);
      bf.rect(0,0,10,10);
      bf.rotateX(PI/2);
      bf.rotateY(PI/2);
      bf.rect(0,0,10,10);
      bf.popMatrix();
    }
  }
}
color c1 = bf.get(mouseX,mouseY);
if (c1 > c2)
  {
    b1.drawball();
    xpos = red(c1)*10;
    ypos = green(c1)*10;
    zpos = blue(c1)*10;
    sz = 10;
  }
}

class Ball
{
 void drawball()
 {
   translate(xpos,ypos,zpos);
   sphere(sz);
 }
}