How to plot TCanvas before program reaches end?

ROOT
1

I have tried following :

#include <iostream>

#include "TH1F.h"
#include "TCanvas.h"
#include "TROOT.h"

int test(){
    gROOT->SetBatch(false);
    TCanvas* canvas = new TCanvas("canvas");
    canvas->cd();
    TH1F* h = new TH1F("name","title", 100, 0, 100);
    h->Fill(10.);
    h->Fill(20.);
    h->Fill(30.);
    h->Draw();
    std::cout<<"I will freeze now"<<std::endl;
    std::cin.get();

    return 0;
}

root test.cpp

and canvas with the histogram is drawn only after the input to cin.get() provided and after test() has returned 0.

I want to pause my program and print canvas while in it…
As you can see I attempted with cin.get() but it doesn’t work…

How one should do it?

cheers,
Bohdan

ROOT Version: 6.24

2

Hi @FoxWise ,
I guess you want something like this:

#include <iostream>
#include <thread>
#include <chrono>

#include "TSystem.h"
#include "TH1F.h"
#include "TCanvas.h"
#include "TROOT.h"

int test(){
    TCanvas* canvas = new TCanvas("canvas");
    canvas->cd();
    TH1F* h = new TH1F("name","title", 100, 0, 100);
    h->Fill(10.);
    h->Fill(20.);
    h->Fill(30.);
    h->Draw();
    canvas->Draw();

    while (true) {
      gSystem->ProcessEvents();
      std::this_thread::sleep_for(std::chrono::milliseconds(10));
    }

    return 0;
}

I guess the missing part is to listen for a keypress and exit the ProcessEvents loop if a key (or just Enter) is pressed. You probably need a separate thread for that that communicates with the main thread via a condition variable, or maybe you can use curses or similar for that purpose.

Cheers,
Enrico

1 Like
3

Oh wow… Didn’t expect “pause” to be so advance in 2021…

My other code parts are most likely not thread-safe. So I would like to stick to one thread if this is possible, of course…

But this is great answer already, thanks!

4

The problem is that you can’t really pause the program: you still want the program to process clicks and interactions with the plot, but you don’t want to proceed further with the program flow.

1 Like
5

I found here that something possible like:

#include <iostream>
#include <ncurses.h>


#include "TSystem.h"
#include "TH1F.h"
#include "TCanvas.h"
#include "TROOT.h"

int test(){
    TCanvas* canvas = new TCanvas("canvas");
    canvas->cd();
    TH1F* h = new TH1F("name","title", 100, 0, 100);
    h->Fill(10.);
    h->Fill(20.);
    h->Fill(30.);
    h->Draw();
    canvas->Draw();

    while ( true ) {
        if (getch() == 'q') break;
      gSystem->ProcessEvents();
      std::this_thread::sleep_for(std::chrono::milliseconds(10));
    }

but ROOT output:

Processing test.cpp...
IncrementalExecutor::executeFunction: symbol 'stdscr' unresolved while linking [cling interface function]!
IncrementalExecutor::executeFunction: symbol 'wgetch' unresolved while linking [cling interface function]!
6

or is it possible to create another root session inside script, and plot temporary saved histo in the root file?

7

The ROOT interpreter doesn’t know that it has to link libcurses against the program. You can probably tell it to, but at this point it might be simpler to use a compiled program.

I’m not sure I understand the question, but if you save the histogram in a ROOT file then you can inspect it from another ROOT session.

Cheers,
Enrico

8

This topic was automatically closed 14 days after the last reply. New replies are no longer allowed.