Formatting colour palette with threshold values

[Wile_E_Coyote]

So, start to remove parts of the source code from the multipalette.C tutorial, which are missing in your own “example”, and see what happens.

[Viesturs]

This “example” draws h1 and h2 on different palettes.

void pal1();
void pal2();
int palette()
{
  TExec * ex1 = new TExec("ex1", "pal1();");
  TExec * ex2 = new TExec("ex2", "pal2();");
  TH2 * h1 = new TH2F("h1", "h1", 2, -0.5, 1.5, 2, -0.5, 1.5);
  h1 -> Fill(0.0, 0.0, 2.0);
  h1 -> Fill(0.0, 1.0, 2.5);

  h1 -> Fill(1.0, 0.0, 0.5);
  h1 -> Fill(1.0, 1.0, 1.5);
  TCanvas * c1 = new TCanvas("c1", "c1", 600, 600);
  h1 -> Draw("COLZ");
  ex1 -> Draw();
  h1 -> Draw("COLZSAME");
  TH2 * h2 = new TH2F("h2", "h2", 2, -0.5, 1.5, 2, -0.5, 1.5);
  h2 -> Fill(0.0, 0.0, 2.0);
  h2 -> Fill(0.0, 1.0, 2.5);
  h2 -> Fill(1.0, 0.0, 0.5);
  h2 -> Fill(1.0, 1.0, 1.5);
  TCanvas *c2 = new TCanvas("c2", "c2", 600, 600);
  h2 -> Draw("COLZ");
  ex2 -> Draw();
  h2 -> Draw("COLZSAME");
  return 0;
}

void pal1()
{
  const unsigned char Number = 6;
  Int_t colours[10];
  static Bool_t initialized = kFALSE;

  Double_t Red[Number]   =  {0.75, 0.75, 0.5, 0.5, 0.2, 0.2,};
  Double_t Green[Number] =  {1.0,  1.0,  1.0, 1.0, 1.0, 1.0 };
  Double_t Blue[Number]  =  {0.75, 0.75, 0.5, 0.5, 0.2, 0.2 };
  Double_t  Stops[Number] = {0.0,  0.5, 0.50001, 0.6, 0.6000001, 1.0};
  TColor::CreateGradientColorTable(Number, Stops, Red, Green, Blue, 10);
}


void pal2()
{
  const unsigned char Number = 6;
  Int_t colours[10];
  Double_t Red[Number]   =  {0.75, 0.75, 0.5, 0.5, 0.2, 0.2,};
  Double_t Green[Number] =  {0.75, 0.75, 0.5, 0.5, 0.2, 0.2 };
  Double_t Blue[Number]  =  {1.0,  1.0,  1.0, 1.0, 1.0, 1.0 };
  Double_t  Stops[Number] = {0.0,  0.5, 0.50001, 0.6, 0.6000001, 1.0};
  TColor::CreateGradientColorTable(Number, Stops, Red, Green, Blue, 10);
}

How should I modify pal2() to enforce the original ROOT palette on h2?

[Wile_E_Coyote]

TStyle::SetPalette

[Viesturs]

That’s very good.
However, when I turn to g++ compilation, I always get an error like this:

input_line_30:2:3: error: use of undeclared identifier 'pal2'
 (pal2())
Error in <HandleInterpreterException>: Error evaluating expression (pal2()).
Execution of your code was aborted.

[Wile_E_Coyote]

For the TExec to work in a standalone compiled code, “pal1” and “pal2” need to be known to the interpreter (i.e., you need a dictionary for them).
I guess the easiest thing to try would be: root palette.cxx++

[couet]

#include <TCanvas.h>
#include <TExec.h>
#include <TH2.h>
#include <TColor.h>

void pal1();

int palette()
{
  TExec * ex1 = new TExec("ex1", "pal1()");
  TExec * ex2 = new TExec("ex2", "gStyle->SetPalette(kBird);");
  TH2 * h1 = new TH2F("h1", "h1", 2, -0.5, 1.5, 2, -0.5, 1.5);
  h1 -> Fill(0.0, 0.0, 2.0);
  h1 -> Fill(0.0, 1.0, 2.5);

  h1 -> Fill(1.0, 0.0, 0.5);
  h1 -> Fill(1.0, 1.0, 1.5);
  TCanvas * c1 = new TCanvas("c1", "c1", 600, 600);
  h1 -> Draw("COLZ");
  ex1 -> Draw();
  h1 -> Draw("COLZSAME");
  TH2 * h2 = new TH2F("h2", "h2", 2, -0.5, 1.5, 2, -0.5, 1.5);
  h2 -> Fill(0.0, 0.0, 2.0);
  h2 -> Fill(0.0, 1.0, 2.5);
  h2 -> Fill(1.0, 0.0, 0.5);
  h2 -> Fill(1.0, 1.0, 1.5);
  TCanvas *c2 = new TCanvas("c2", "c2", 600, 600);
  h2 -> Draw("COLZ");
  ex2 -> Draw();
  h2 -> Draw("COLZSAME");
  return 0;
}

void pal1()
{
  const unsigned char Number = 6;
  Int_t colours[10];
  static Bool_t initialized = kFALSE;

  Double_t Red[Number]   =  {0.75, 0.75, 0.5, 0.5, 0.2, 0.2,};
  Double_t Green[Number] =  {1.0,  1.0,  1.0, 1.0, 1.0, 1.0 };
  Double_t Blue[Number]  =  {0.75, 0.75, 0.5, 0.5, 0.2, 0.2 };
  Double_t  Stops[Number] = {0.0,  0.5, 0.50001, 0.6, 0.6000001, 1.0};
  TColor::CreateGradientColorTable(Number, Stops, Red, Green, Blue, 10);
}

Executed with:

% root palette.cxx++
   ------------------------------------------------------------------
  | Welcome to ROOT 6.25/01                        https://root.cern |
  | (c) 1995-2021, The ROOT Team; conception: R. Brun, F. Rademakers |
  | Built for macosx64 on May 12 2021, 13:05:12                      |
  | From heads/master@v6-25-01-953-g2c784fd2d4                       |
  | With Apple clang version 12.0.5 (clang-1205.0.22.9)              |
  | Try '.help', '.demo', '.license', '.credits', '.quit'/'.q'       |
   ------------------------------------------------------------------

root [0] 
Processing palette.cxx++...
Info in <TMacOSXSystem::ACLiC>: creating shared library ./palette_cxx.so
(int) 0
root [1] 

Gives:

[Viesturs]

I managed to integrate TExec also in a C++ project.