%%cpp -d

void canvasRefresh(TCanvas *c1)
{
   for (Int_t j = 0; j < 3; j++)
      c1->GetPad(j+1)->Modified();

   c1->Modified();
   c1->Update();

   gSystem->ProcessEvents();
}

TCanvas* c1 = new TCanvas("c1","Dynamic Filling Example",200,10,600,900);

TH1 *hpx[3];
hpx[0]    = new TH1F("hp0","Normal histogram",1000,-4,4);
hpx[1]    = new TH1K("hk1","Nearest Neighbour of order 3",1000,-4,4);
hpx[2]    = new TH1K("hk2","Nearest Neighbour of order 16",1000,-4,4,16);
c1->Divide(1,3);
for (Int_t j = 0; j < 3; j++) {
   c1->cd(j + 1);
   hpx[j]->SetFillColor(48);
   hpx[j]->Draw();
}

gRandom->SetSeed(12345);
Float_t px, py, pz;
const Int_t kUPDATE = 10;
for (Int_t i = 0; i <= 300; i++) {
   gRandom->Rannor(px,py);
   for (Int_t j = 0; j < 3; j++)
      hpx[j]->Fill(px);
   if (i && (i % kUPDATE) == 0)
      canvasRefresh(c1);
}

for (Int_t j = 0; j < 3; j++)
   hpx[j]->Fit("gaus");

canvasRefresh(c1);

gROOT->GetListOfCanvases()->Draw()