Introduce Qt6-based implementation for `TCanvasImp` by linev · Pull Request #22736 · root-project/root

linev · 2026-07-01T10:41:20Z

After setting Gui.Factory: qt6 TQt6Canvas canvas implementation will be created in ROOT.

Painting with TQt6PadPainter redirected to QPainter class where all ROOT primitives -
polyline, fillarea, polymarkers, line, box, text - are implemented.
Mouse click/move/release/wheel/enter/leave events are processed.
Menu implemented with QMenuBar, toolbar with QToolBar, status line with QStatusBar.

Also context menu is implemented providing TQt6ContextMenuImp class.
It includes special dialog for input of method parameters.
Also toggle menu item with checked states should work.

Simple dialogs for line, fill, text and marker attributes are implemented.
For now they invoked when correspondent context menu command is activated,
later one can provide better integration via gui factory.

Provided implementation fully avoids gVirtualX usage - pure Qt graphics is used.
TQt6Canvas works now with basic primitives like TLatex, TLine, TBox
and with TH1/TH2 classes in 2D and 3D plots.
Some ROOT classes may crash while they internally use gVirtualX for event handling.
These classes will be fixed/improved later.

Classes declared in ROOT::Experimental namespace. I re-wrote commits history (took 1.5 hours) to have classes defined from the beginning as experimental. These are:

ROOT::Experimental::TQt6Canvas
ROOT::Experimental::TQt6PadPainter
ROOT::Experimental::TQt6GuiFactory
ROOT::Experimental::TQt6Application

There are know problems/issues/open questions:

running of Qt and ROOT event loop together. Now ROOT TApplication invokes qt events per timer, but one can have opposite situation when ROOT classes used from QApplication. At least our API should be capable to handle both situations.
one has to prevent gVirtualX/gClient initialization completely, now only gClient is skipped
no browser, no fitpanel, no treeviewer; TGuiFactory can create them, but do we want to implement them for alternative graphics backends; do we want to reuse TRootBrowser or RBrowser code?
probably we need switch for root executable like root --backend=qt6; there are more backends expected
text allign is not identical (one or two pixels difference) with gVirtualX implementation, need to be investigated
not all canvas menu commands are provided, probably one can move some functionality to base classes;
no public API yet to reuse canvas in external Qt6-based projects, to be defined in the future

This is first (but not the only) new graphical backend which can fully replace gVirtualX-based implementation.
After finalizing of API some other - more simpler (like raylib) or more advanced (like Vulkan) - can be exercised.

silverweed

I started reviewing this PR and made it about 10 commits in, but it seems to me that this is still in a state not ready for review: there are several commits where something is introduced and later changed in other commits, as well as many leftovers of commented-out code and debug prints.

Please try reorganizing the commits in a more review-friendly manner to help understanding what is going on (and also to not leave many commits with an incomplete state in the history when this is merged)

linev · 2026-07-29T13:08:27Z

@silverweed

I know that commits are not looking perfect - but they show the way how I develop the code.
They always compiled and in most cases functional to some extend.

I use a lot code from our go4 project where QtRoot canvas with TVirtaulX-based graphics is used. Whats why in original commits code appears which than removed or significantly changed.

Such big development will never be linear and clear.
My aim - not sorting commits nicely but produce finally code which works.
Internal API will be changed many times anyway.
Most probably class names will be changed.
Even original folder name qt6canvas will be changed - while already now it is more than TQt6Canvas.

But this is the way how software is developed.
Otherwise ROOT repository will consists not from 90K commits but from 100 - by number of our releases.

silverweed · 2026-07-29T14:08:11Z

But this is the way how software is developed.
Otherwise ROOT repository will consists not from 90K commits but from 100 - by number of our releases.

This is such a mischaracterization of what I asked that I don't know what to say about it. Just, that PRs and commits in a team project should not look as they would if you were developing the software by yourself, otherwise whoever reviews this code will have a much harder time understanding it properly, which is the point of reviewing it in the first place.

linev · 2026-07-29T14:27:10Z

My point is - rewriting/reorganizing commits now makes no sense.

There are fundamental problems which should be resolved and discussed:

way how invocation of TCanvas::Update() match to Qt logic; is same will work with absolutely different GUI libs
handling of mouse/keyboard events; nicely works with Qt, can be a mess in other cases
running several canvases with their menus/dialogs in parallel (now it is not yet possible),
coexistence of QApplication and TApplication with their events loops (works in go4, but in opposite way as it runs in this prototype)
running ROOT graphics/gpad classes without loading X11/Cocoa/TWin32gdk libraries and when gVirtualX and gClient are nullptr.

All kind of debug output, commented out code, unused variables, compiler warnings can be resolved once such crucial points are proved to be working.

github-actions · 2026-07-29T19:41:40Z

Test Results

23 files 23 suites 3d 13h 48m 32s ⏱️
3 853 tests 3 853 ✅ 0 💤 0 ❌
78 505 runs 78 505 ✅ 0 💤 0 ❌

Results for commit 7037a68.

♻️ This comment has been updated with latest results.

Support special fill patterns 3000..3025 reusing X11 pixmaps Implement box and fillarea painting

Once generic API exists to paint markers - use it here instead. There are 5 different places in ROOT which repeats again and again all markers implementation

It is not equivalent with TTF font and must be about 0.75

Use QString::toLatin1() method, otherwise special characters like used in symbols.ttf, are handled as utf-8 as displayed wrongly

Like press, move, release mouse button. On the right mouse button actiate context menu. For methods with arguments provide special dialog. Code partially copied from Go4 project and originally was developed in 2002 by Denis Bertini and improved later by Sergey Linev

It fully dismiss standard GUI classes and only allows to create Qt6canvas. Aim to provide specialized implementation for application and context menu Declare it in ROOT::Experimental namespace

It is implementation for context menu used inside qt6_canvas Idea to let handle right mouse button click in the canvas handler which will invoke implementation class

This is default place where all normal or custom items for the class are collected. By large copy code from TRootContextMenu.

Reuse several methods from TContextMenu to create labels for arguments and afterwards execute selected method with provided list of arguments.

These are: * open ROOT file, * Save as dialog * Menu items with supported formats Use QFileDialog, list of supported extensions can be moved later to base class

Implement toggling of empty QToolBar Implement toggling of status branch Implement tooltip event handling and toggling of such mode

For line, fill, text, marker attributes provide dialogs to avoid ROOT crash while default editors does not work in Qt For all attributes reuse colors editors with opacity

Required for zooming and corrects interactivity handling in ROOT

Add \class mark for all used classes Provide some remarks around QPainter and paintEvent handler Remove several debugging printf Make headers #ifdef with same syntax

Idea to move dedicated application initialization there

When TQt6Application is created immediately create also QApplication. In the future one can make it optional

Gives information to application that virtualx is not required.

Use new TAttMarker::GetMarkerShape() method

Prevent access to nullptr Prevent out-of-bound access to markers Remove timeout from mouse handling AI-assist with qwen llmbot

jblomer

In principle looks good to me! I went commit by commit, some comments are invalidated by later commits, feel free to ignore them.

Are the Q... classes visible as symbols? If so, I think they should go in ROOT::Internal (can be another PR).

linev · 2026-09-21T06:37:46Z

@jblomer

I will merge PR and will try to create next one with my newer changes - TTF implementation and basic graphics editors.

Many comments are valuable, but can be considered when final implementation will be done. Currently code changes rapidly, methods appears and then removed again. At its final stage TQt6PadPainter will be much more compact and lines which are discussed now simply disappear. Same with TQt6Canvas - lot of gVirtualX-related methods will be gone. Therefore I see no needs to already now make each commit and each comment perfect.

linev self-assigned this Jul 1, 2026

linev requested a review from bellenot as a code owner July 1, 2026 10:41

linev added the affects:master label Jul 1, 2026

linev requested review from dpiparo and pcanal as code owners July 1, 2026 10:41

linev added in:Graphics skip ci Skip the full builds on the actions runners labels Jul 1, 2026

linev marked this pull request as draft July 1, 2026 10:41

linev mentioned this pull request Jul 1, 2026

Remove gVirtualX usage in TGaxis and TView3D #22737

Merged

linev force-pushed the qt6_canvas branch from 40f1d1b to ba899cf Compare July 2, 2026 07:45

silverweed self-requested a review July 8, 2026 07:12

linev force-pushed the qt6_canvas branch 5 times, most recently from 5f7c92a to bf253b8 Compare July 29, 2026 08:04

linev changed the title ~~[EXPERIMENTAL] Introduce Qt6-based implementation for TCanvasImp [skip-ci]~~ Introduce Qt6-based implementation for TCanvasImp Jul 29, 2026

linev removed the skip ci Skip the full builds on the actions runners label Jul 29, 2026

linev marked this pull request as ready for review July 29, 2026 08:34

linev requested a review from couet July 29, 2026 08:35

linev closed this Jul 29, 2026

linev reopened this Jul 29, 2026

linev force-pushed the qt6_canvas branch from bf253b8 to 82be338 Compare July 29, 2026 11:29

silverweed previously requested changes Jul 29, 2026

View reviewed changes

linev force-pushed the qt6_canvas branch from 82be338 to 3a16a84 Compare July 29, 2026 12:24

linev force-pushed the qt6_canvas branch from 3a16a84 to 32ca3a8 Compare July 29, 2026 14:44

linev added 21 commits August 17, 2026 14:56

[qt6canv] implement fill styles

18cfa90

Support special fill patterns 3000..3025 reusing X11 pixmaps Implement box and fillarea painting

[qt6canv] simple marker painting

bca6427

Once generic API exists to paint markers - use it here instead. There are 5 different places in ROOT which repeats again and again all markers implementation

[qt6canv] use scaling factor for the QFont size

2712746

It is not equivalent with TTF font and must be about 0.75

[qt6canv] correctly convert const char * to QString

9b26716

Use QString::toLatin1() method, otherwise special characters like used in symbols.ttf, are handled as utf-8 as displayed wrongly

[qt6canv] provide cursors and window title and size

1570b0a

[qt6canv] introduce TQt6GuiFactory

c2ecc9f

It fully dismiss standard GUI classes and only allows to create Qt6canvas. Aim to provide specialized implementation for application and context menu Declare it in ROOT::Experimental namespace

[qt6canv] introduce QRootContextMenu

9dfe218

It is implementation for context menu used inside qt6_canvas Idea to let handle right mouse button click in the canvas handler which will invoke implementation class

[qt6canv] use list of TContextMenuItem from TClass

d2995d4

This is default place where all normal or custom items for the class are collected. By large copy code from TRootContextMenu.

[qt6canv] implement arguments dialog for context menu

6c2e5f6

Reuse several methods from TContextMenu to create labels for arguments and afterwards execute selected method with provided list of arguments.

[qt6canv] implement File menu commands

7d5a229

These are: * open ROOT file, * Save as dialog * Menu items with supported formats Use QFileDialog, list of supported extensions can be moved later to base class

[qt6canv] add View menu items

a15645f

Implement toggling of empty QToolBar Implement toggling of status branch Implement tooltip event handling and toggling of such mode

[qt6canv] implement most buttons in toolbar

0ffff3a

[qt6canv] provide basic attributes editors

e6fc2de

For line, fill, text, marker attributes provide dialogs to avoid ROOT crash while default editors does not work in Qt For all attributes reuse colors editors with opacity

[qt6canv] add enter/leave/wheel handlers

4d63bdb

Required for zooming and corrects interactivity handling in ROOT

[qt6canv] provide more documentation

816a872

Add \class mark for all used classes Provide some remarks around QPainter and paintEvent handler Remove several debugging printf Make headers #ifdef with same syntax

[qt6canv] introduce specialized TApplicationImp class

38edab6

Idea to move dedicated application initialization there

[qt6canvas] move QApplication initialization to TQt6Application class

df6388b

When TQt6Application is created immediately create also QApplication. In the future one can make it optional

[qt6canvas] return false in TQt6GuiFactory::UseVirtualX()

93c95b5

Gives information to application that virtualx is not required.

[qt6canvas] implement markers painting

9d38d41

Use new TAttMarker::GetMarkerShape() method

[qt6canvas] add several checks and missing includes

a7fecce

Prevent access to nullptr Prevent out-of-bound access to markers Remove timeout from mouse handling AI-assist with qwen llmbot

linev force-pushed the qt6_canvas branch from 7037a68 to a7fecce Compare August 17, 2026 12:56

linev mentioned this pull request Aug 27, 2026

[gui] Native GUI draws canvas without defaulting to web #23163

Closed

2 of 4 tasks

couet removed their request for review September 1, 2026 09:02

jblomer approved these changes Sep 15, 2026

View reviewed changes

linev requested a review from silverweed September 21, 2026 07:32

linev merged commit bc9232d into root-project:master Sep 21, 2026
29 of 33 checks passed

linev deleted the qt6_canvas branch September 21, 2026 07:45

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