How to draw multiple surfaces with intersections?

[Ako_b]

Hello!
I need to draw two surfaces on the same canvas, namely TGraph2D with TRI1 option and its fit with TF2 with SURF1 option.
I made very simple example:

{
  TF2 f1("f1", "x^2 + y^2", -3, 3, -3, 3);
  TF2 f2("f2", "x + y + 5", -3, 3, -3, 3);
  f1.Draw("surf1");
  f2.Draw("surf1 same");
  
  f1.SetMinimum(0.0);
  f1.SetMaximum(18.0);
  f2.SetMinimum(0.0);
  f2.SetMaximum(18.0);
}

However, I get this:

Currently I have to export data to Octave, where I can get nice plots like this:

where I can clearly see if fitted surface matches data.

Is there any way to draw multiple surfaces properly in ROOT?

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ROOT Version: 6.26/06
Platform: CentOS 7 x86_64
Compiler: gcc (GCC) 12.2.0

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[couet]

void ako()
{
  auto f1 = new TF2("f1", "x^2 + y^2", -3, 3, -3, 3);
  auto f2 = new TF2("f2", "x + y + 5", -3, 3, -3, 3);

  f1->SetMinimum(0.0);
  f1->SetMaximum(18.0);
  f2->SetMinimum(0.0);
  f2->SetMaximum(18.0);
  f2->Draw("surf1");
  f1->Draw("surf1 same");

}

[Ako_b]

Thanks for your response, @couet! My apologies, probably my first example is a bit misleading. Here’s a more obvious one.

void ako()
{
  TF2 f1("f1", "x - y + 5", -3, 3, -3, 3);
  TF2 f2("f2", "x + y + 5", -3, 3, -3, 3);

  
  f1.SetMinimum(0.0);
  f1.SetMaximum(10.0);
  f2.SetMinimum(0.0);
  f2.SetMaximum(10.0);

  f1.Draw("surf1");
  f2.Draw("surf1 same");
}

What I get vs what I expect:

I mean, seems like order of Draw calls doesn’t matter here. Am I missing some simple option?

[couet]

Ah yes, this will not work. The two surfaces ignore each other.
May have a look at ROOT: THistPainter Class Reference
And the GL option after.

[Ako_b]

Sorry for late reply.
Using TGLHistPainter produces same behavior, and it seems that SAME option doesn’t work properly.

void ako() {
  gStyle->SetCanvasPreferGL(true);

  TF2 f1("f1", "x - y + 5", -3, 3, -3, 3);
  TF2 f2("f2", "x + y + 5", -3, 3, -3, 3);
  
  f1.SetMinimum(0.0);
  f1.SetMaximum(10.0);
  f2.SetMinimum(0.0);
  f2.SetMaximum(10.0);

  f1.Draw("glsurf1");
  f2.Draw("glsurf1 same");
}

Regarding TF3, I’ve managed to get sensible result with this approach:

{
  auto f3 = new TF3("f3","(x - y + 5 - z) * (x + y + 5 - z)",-3,3,-3,3,-2,12);
  f3->SetFillColor(30);
  f3->SetLineColor(15);
  f3->SetNpz(100);
  f3->Draw("fb bb");
}

However, it’s not clear how to apply it to my case of visual comparison of TGraph2D and its fit with TF2. I need to convert TGraph2D into implicit 3d function somehow.

So far, I will just continue to use Octave as simplest solution.
Anyway, thank you for help!

[couet]

With TGraph2D you cannot have surfaces with several z values for one (x,y) pair.