[ThePhisch]

When drawing a canvas in a native GUI (e.g. using
tutorials/visualisation/gui/guitest.C and Test->Dialog->Tab3), the canvas used to default to black. The workaround was --web=off, which is inconvenient.

Implements a new method TGuiFactory::CreateCanvasImpNative that bypasses the gROOT->IsWebDisplay() check and directly returns a TCanvasImp as required by the native GUI.

TGuiFactory::CreateCanvasImp receives TCanvas *c as a parameter. For a web canvas, the canvas ID is 111222333 (see TWebCanvas.cxx:293), this would be enough to determine that we do not want to create a web canvas element, but a native one instead. However, TCanvas is only forward declared within TGuiFactory, hence we cannot access its methods.

Checklist:

• tested changes locally
• updated the docs (not necessary)
• added tests (not sure how to write a test for this behaviour)
• ran clang-format

AI Disclaimer

I used AI in the debugging process, but I wrote the code myself. It is a very small edit anyway.

[linev]

This is wrong approach.

TGuiFactory is "native" at the moment when instantiated in the ROOT application.
And it has necessary methods to create implementation for canvas.

Code cannot work - while it only provides basic TCanvasImp instance which has no real implementation and only created in batch mode.

I see no problem with guitest.C macro - nor in master neither in the released ROOT version 6.40.x

We are follow now different strategy to extend existing TGuiFactory/TCanvasImp classes to be able provide real alternatives for current TVirtualX-based graphics and guis. See PR for such example #22736

[linev]

I close PR as wan't merge

[ThePhisch]

This is wrong approach.

TGuiFactory is "native" at the moment when instantiated in the ROOT application. And it has necessary methods to create implementation for canvas.

Code cannot work - while it only provides basic TCanvasImp instance which has no real implementation and only created in batch mode.

I see no problem with guitest.C macro - nor in master neither in the released ROOT version 6.40.x

We are follow now different strategy to extend existing TGuiFactory/TCanvasImp classes to be able provide real alternatives for current TVirtualX-based graphics and guis. See PR for such example #22736

are you running on linux or MacOS? I should have mentioned that I have this issue on MacOS.

This is what it looks like:

This is what is should look like (i.e. with the workaround root --web=off

This is guitest.C on 6.40.02 running on Tahoe 26.3.1 (a)

[linev]

On Mac I see no problem on master, 6.40 and 6.38 branches.

Do you have special rootlogon.C macro or .rootrc file in current directory?

[ThePhisch]

On Mac I see no problem on master, 6.40 and 6.38 branches.

Do you have special rootlogon.C macro or .rootrc file in current directory?

It was my .rootrc file that caused the issue. Thank you for helping me catch that.