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Description

Documentation for TCanvas::Divide says:

Automatic pad generation by division.

• The current canvas is divided in nx by ny equal divisions (pads).
• xmargin is the space along x between pads in percent of canvas.
• ymargin is the space along y between pads in percent of canvas.
• color is the color of the new pads. If 0, color is the canvas color.

But setting margins to 0 results in:

1. Not setting up colors of subpards
2. Adding top-right padding to the main canvas.

The documentation also says that:

Note3: in case xmargin <=0 and ymargin <= 0, there is no space between pads. The current pad margins are recomputed to optimize the layout.

Not sure what the second sentence means, what pad margins are recomputed?

Reproducer

Here a couple of examples of proper and improper behaviors:

1. This works as expected - OK

{
    TCanvas * can = new TCanvas("can", "can", 800, 800);
    can->Divide(2, 2, 0.01, 0.01, 2);
}

2. This gives white pads whereas they should be red - NOT OK

{
    TCanvas * can = new TCanvas("can", "can", 800, 800);
    can->Divide(2, 2, 0.0, 0.0, 2);
}

3. After putting colours manually, we see odd top-right margin - NOT OK

{
    TCanvas * can = new TCanvas("can", "can", 800, 800);
    
    can->Divide(2, 2, 0.0, 0.0, 2);
    
    can->cd(1);
    gPad->SetFillColor(30);
    gPad->Modified();
    gPad->Update();
    
    can->cd(2);
    gPad->SetFillColor(38);
    gPad->Modified();
    gPad->Update();
    
    can->cd(3);
    gPad->SetFillColor(41);
    gPad->Modified();
    gPad->Update();
    
    can->cd(4);
    gPad->SetFillColor(42);
    gPad->Modified();
    gPad->Update();
    
    can->cd(0);
    gPad->SetFillColor(2);
    gPad->Modified();
    gPad->Update();
}

ROOT version

ROOT v6.36.04
Built for linuxx8664gcc on Sep 05 2025, 08:28:36
From tags/6-36-04@6-36-04
With 
Binary directory: /usr/bin

Installation method

Gentoo, build from sources

Operating system

Gentoo

Additional context

No response