Live update plot broken on MacOS

[vepadulano]

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Description

Updating a plot is broken on MacOS. I assume this worked at some point since we have a tutorial https://root.cern/doc/master/hist007__TH1__liveupdate_8C.html

The same piece of code does not update the plot on MacOS, whereas on Linux the plot is updated (see reproducer below)

Just for reference @linev , plotting with webgraphics correctly updates the plot both on MacOS and Linux but:

• It is much much slower
• On MacOS the plotting window didn't open automatically, I had to manually switch the view to the browser window in order to see the plot.

Reproducer

$: root -l live_update.C

std::unique_ptr<TH1D> h;
std::unique_ptr<TCanvas> c;

void live_update()
{
   c = std::make_unique<TCanvas>();
   h = std::make_unique<TH1D>("h", "h", 100, -5, 5);

   h->Draw();
   c->Update();
   for (auto i = 0; i < 1000; i++){
      h->FillRandom("gaus", 10);
      c->Modified();
      c->Update();
   }
}

ROOT version

master

Installation method

build from source

Operating system

MacOS

Additional context

No response

[dpiparo]

@vepadulano is this also broken on 6.38 or only master?

[couet]

The same piece of code does not update the plot on MacOS

@vepadulano :
This is known. Mac is special, you need to call ModifiedUpdate -> https://root.cern/doc/master/classTPad.html#a8bcdba74eef3d08c66148c7182a5681b in a such case

I'll provide a PR

[vepadulano]

@couet ,

Thank you for sharing this crucial nugget of knowledge!

I think one could hardly say that this situation is known: the TPad::ModifiedUpdate method was introduced in ROOT 6.32, it was never documented in a way that a user could understand if/when this method should be used compared with, say, TPad::Update or TPad::Modified, and it is never used anywhere else in the codebase.

Now that I know that this method exists, I can use it as an example in #21243. I will also propose to modify the hist007 tutorial accordingly.

Cheers.

[couet]

PR: #21363

[github-actions]

Hi @vepadulano, @couet,

It appears this issue is closed, but wasn't yet added to a project. Please add upcoming versions that will include the fix, or 'not applicable' otherwise.

Sincerely,
🤖