void DrawIt()
{
  ClearWindowText;
}

void BSpline()
{
  GrBitMap *b=GrNew(grbase);
  I8 p1,p2,i=0,cmd;
  U4 old_update_window=Fs->update_window;
  U4 old_ip_double=Bts(&Fs->crt_flags,CRTf_NO_DOUBLE_CLICK);
  U4 old_inhibit=ip_inhibit_win_operations;
  P3I4 c[64];
  ip_inhibit_win_operations=TRUE;
  Fs->update_window=&DrawIt;
  GrClear;
  do {
    cmd=GetMsg(&p1,&p2,1<<MSG_IP_L_UP+1<<MSG_IP_R_UP);
    if (cmd==MSG_IP_L_UP) {
      c[i].x=p1; c[i].y=p2; c[i].z=0;
      b->color=GR_GREEN^GR_WHITE;
      GrCircle(b,p1,p2,10);
      i++;
    }
  } while (cmd!=MSG_IP_R_UP);
  b->color=GR_RED^GR_WHITE;
  Gr2BSpline(b,c,i,TRUE);
  b->color=GR_BLUE^GR_WHITE;
  Gr3BSpline(b,c,i,TRUE);
  AssignBit(&Fs->crt_flags,CRTf_NO_DOUBLE_CLICK,old_ip_double);
  Fs->update_window=old_update_window;
  ip_inhibit_win_operations=old_inhibit;
}

BSpline; 