void BSplineDemo()
{
  GrBitMap *b=GrAlias(Gs->grbase,Fs);
  I8 p1,p2,i=0,cmd;
  BoolU4 old_inhibit=ip_inhibit_win_operations;
  BoolU4 old_ip_double=Bts(&Fs->crt_flags,CRTf_NO_DOUBLE_CLICK);
  P3I4 c[64];
  ip_inhibit_win_operations=TRUE;
  PutS("$$CL$$");
  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=GREEN^WHITE;
      GrCircle(b,p1,p2,10);
      i++;
    }
  } while (cmd!=MSG_IP_R_UP);
  b->color=RED^WHITE;
  Gr2BSpline(b,c,i,TRUE);
  b->color=BLUE^WHITE;
  Gr3BSpline(b,c,i,TRUE);
  AssignBit(&Fs->crt_flags,CRTf_NO_DOUBLE_CLICK,old_ip_double);
  ip_inhibit_win_operations=old_inhibit;
  GrDel(b);
}

BSplineDemo;

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