PGraphics back;
Ball ball;

void setup () {
    size(300,200);
    
    back = createGraphics(width*4, height, P3D);
    back.beginDraw();
    back.background(0xFFFFFFFF);
    int i = 0;
    while ( i<width*4  )
    {
	  back.stroke(0xFF000000); back.strokeWeight(1); noFill();
	  back.line(i,0,i,height);
	  i+=(int)random(5);
    }
    back.endDraw();
    
   ball = new Ball(width/2,height/2); 
}

void draw()
{
    background(0xFFFF0000);
    
    if ( mousePressed )
    {
	  back.beginDraw();
	  back.noStroke(); back.fill(0xFFFF0000);
	  back.ellipse( mouseX+ball.x*3, mouseY, 10, 10 );
	  back.endDraw();
    }
    image(back,-ball.x*3,0);
    
    ball.move();
    ball.draw();
}

class Ball
{
    float x,y;
    float xx, yy;
    Ball ( float _x, float _y )
 {
     x = _x; y = _y;
     xx = random(0,2);
     yy = random(0,2);
 }   
 void move()
 {
     x += xx; y += yy;
     if ( x < 0 || x > width ) xx = -xx;
     if ( y < 0 || y > height ) yy = -yy;
 }
 void draw ()
 {
     ellipse(x,y,5,5);
 }
}