doc/v606/DynamicSlice_8C.html

void DynamicSlice()

{

   // Create a new canvas.

   c1 = new TCanvas("c1","Dynamic Slice Example",10,10,700,500);

   c1->SetFillColor(42);

   c1->SetFrameFillColor(33);


   //create a 2-d histogram, fill and draw it

   TH2F *hpxpy  = new TH2F("hpxpy","py vs px",40,-4,4,40,-4,4);

   hpxpy->SetStats(0);

   Double_t px,py;

   for (Int_t i = 0; i < 50000; i++) {

      gRandom->Rannor(px,py);

      hpxpy->Fill(px,py);

   }

   hpxpy->Draw("col");


   //Add a TExec object to the canvas

   c1->AddExec("dynamic","DynamicExec()");

}


void DynamicExec()

{

   // Example of function called when a mouse event occurs in a pad.

   // When moving the mouse in the canvas, a second canvas shows the

   // projection along X of the bin corresponding to the Y position

   // of the mouse. The resulting histogram is fitted with a gaussian.

   // A "dynamic" line shows the current bin position in Y.

   // This more elaborated example can be used as a starting point

   // to develop more powerful interactive applications exploiting Cling

   // as a development engine.


   TObject *select = gPad->GetSelected();

   if(!select) return;

   if (!select->InheritsFrom(TH2::Class())) {gPad->SetUniqueID(0); return;}

   TH2 *h = (TH2*)select;

   gPad->GetCanvas()->FeedbackMode(kTRUE);


   //erase old position and draw a line at current position

   int pyold = gPad->GetUniqueID();

   int px = gPad->GetEventX();

   int py = gPad->GetEventY();

   float uxmin = gPad->GetUxmin();

   float uxmax = gPad->GetUxmax();

   int pxmin = gPad->XtoAbsPixel(uxmin);

   int pxmax = gPad->XtoAbsPixel(uxmax);

   if(pyold) gVirtualX->DrawLine(pxmin,pyold,pxmax,pyold);

   gVirtualX->DrawLine(pxmin,py,pxmax,py);

   gPad->SetUniqueID(py);

   Float_t upy = gPad->AbsPixeltoY(py);

   Float_t y = gPad->PadtoY(upy);


   //create or set the new canvas c2

   TVirtualPad *padsav = gPad;

   TCanvas *c2 = (TCanvas*)gROOT->GetListOfCanvases()->FindObject("c2");

   if(c2) delete c2->GetPrimitive("Projection");

   else   c2 = new TCanvas("c2","Projection Canvas",710,10,700,500);

   c2->SetGrid();

   c2->cd();


   //draw slice corresponding to mouse position

   Int_t biny = h->GetYaxis()->FindBin(y);

   TH1D *hp = h->ProjectionX("",biny,biny);

   hp->SetFillColor(38);

   char title[80];

   sprintf(title,"Projection of biny=%d",biny);

   hp->SetName("Projection");

   hp->SetTitle(title);

   hp->Fit("gaus","ql");

   hp->GetFunction("gaus")->SetLineColor(kRed);

   hp->GetFunction("gaus")->SetLineWidth(6);

   c2->Update();

   padsav->cd();

}