void userdraw() {
	point2D_t bola[360],pc;
	static int sw=0;
	static float tick=0,dtick=0.01;
	static float d=0,r[360];
	static point2D_t pb[360];
	static float batas[4], dx[360], dy[360];
	color_t putih={1,1,1};
	static color_t col[320];
	int i,n=20;
	point2D_t kb[4]={{0,0},{80,0},{80,60},{0,60}};
	color_t wk[4]={{1,0,0},{0,1,0},{0,0,1},{1,1,1}};
	color_t w1[4]={{0,0,0.5},{0,0,0.5},{0.1,0.5,1},{0.1,0.5,1}};

	if(sw==0){
		for(i=0;i<n;i++){
			pb[i].x=30+(float)20*rand()/RAND_MAX;
			pb[i].y=20+(float)20*rand()/RAND_MAX;
			dx[i]=(float)0.3*rand()/RAND_MAX+0.1;
			dy[i]=(float)0.3*rand()/RAND_MAX+0.1;
			col[i].r=0.5+(float)0.5*rand()/RAND_MAX;
			col[i].g=0.5+(float)0.5*rand()/RAND_MAX;
			col[i].b=0.5+(float)0.5*rand()/RAND_MAX;
			r[i]=0.5*rand()/RAND_MAX+1.;
		}
	}

	// Mewarnai frame
	gradatePolygon(kb,wk,4);

	// Membuat Garis Batas
	batas[0]=(float)10+tick;
	batas[1]=(float)50-tick;
	batas[2]=(float)10+tick;
	batas[3]=(float)70-tick;
	point2D_t kotak[4];
	kotak[0].x=batas[2];
	kotak[1].x=batas[3];
	kotak[2].x=batas[3];
	kotak[3].x=batas[2];
	kotak[0].y=batas[0];
	kotak[1].y=batas[0];
	kotak[2].y=batas[1];
	kotak[3].y=batas[1];
	gradatePolygon(kotak,w1,4);
	setColor(0,0.1,0.6);
	drawPolygon(kotak,4);

	for(i=0;i<n;i++){

	// Membuat bola dengan titikpusat pb
	// dan jari2 1.5
	createCircle(bola,pb[i],r[i]);
	// menggambar bola
	pc.x=pb[i].x+0.5;
	pc.y=pb[i].y+0.5;
	centerPolygon(bola,pc,col[i],putih,360);

	// Menggerakkan titik pusat bola
	pb[i].x=pb[i].x+dx[i];
	pb[i].y=pb[i].y+dy[i];
	// Border Detection
	if((pb[i].x<batas[2]+2) | (pb[i].x>batas[3]-2)){
		dx[i]=-dx[i];
		pb[i].x=pb[i].x+dx[i];
	}
	if((pb[i].y<batas[0]+2) | (pb[i].y>batas[1]-2)){
		dy[i]=-dy[i];
		pb[i].y=pb[i].y+dy[i];
	}
	}
	tick+=dtick;
	if(tick>8 || tick<0) dtick=-0.0001*dtick;
	sw++;
}