Surf1, surf2, etc options

Options “SURF”, “SURF1” and “SURF3” draw a “mesh” made of (thin) lines.
The problem with your histogram is that it has 1000 bins in X and Y directions, so the drawn “mesh” (one thin line for each bin in both directions) makes the whole picture completely “black”.
Try: { TFile *f = TFile::Open("cors_plot-gammatot.root"); TH2F *h; f->GetObject("hallrxry", h); TCanvas *c = new TCanvas("c", "c"); c->SetLogz(1); h->Draw("SURF2"); // "SURF2" or "SURF7" or "SURF4" }