[EXPERIMENTAL] Introduce Qt6-based implementation for TCanvasImp [skip-ci]

.github/CODEOWNERS

@@ -67,6 +67,7 @@
 /gui/webdisplay/ @linev
 /gui/cefdisplay/ @linev
 /gui/qt6webdisplay/ @linev
+/gui/qt6canvas/ @linev
 /gui/webgui6/ @linev
 /gui/fitpanelv7/ @linev
 /gui/browsable/ @bellenot @linev

.github/workflows/root-ci-config/buildconfig/global.txt

@@ -63,6 +63,7 @@ opengl=ON
 pyroot=ON
 pythia8=OFF
 qt6web=OFF
+qt6canv=OFF
 roofit=ON
 roofit_multiprocess=OFF
 root7=ON

cmake/modules/RootBuildOptions.cmake

@@ -147,6 +147,7 @@ ROOT_BUILD_OPTION(mpi OFF "Enable support for Message Passing Interface (MPI)")
 ROOT_BUILD_OPTION(opengl ON "Enable support for OpenGL (requires libGL and libGLU)")
 ROOT_BUILD_OPTION(pyroot ON "Enable support for automatic Python bindings (PyROOT)")
 ROOT_BUILD_OPTION(pythia8 OFF "Enable support for Pythia 8.x [GPL]")
+ROOT_BUILD_OPTION(qt6canv OFF "Enable Qt6 canvas (requires Qt6::Gui)")
 ROOT_BUILD_OPTION(qt6web OFF "Enable support for Qt6 web-based display (requires Qt6::WebEngineCore and Qt6::WebEngineWidgets)")
 ROOT_BUILD_OPTION(roofit ON "Build the advanced fitting package RooFit, and RooStats for statistical tests. If xml is available, also build HistFactory.")
 ROOT_BUILD_OPTION(roofit_multiprocess OFF "Build RooFit::MultiProcess and multi-process RooFit::TestStatistics classes (requires ZeroMQ >= 4.3.5 built with -DENABLE_DRAFTS and cppzmq).")
@@ -222,6 +223,7 @@ if(all)
  set(opengl_defvalue ON)
  set(pythia8_defvalue ON)
  set(pyroot_defvalue ON)
+ set(qt6canv_defvalue ON)
  set(qt6web_defvalue ON)
  set(r_defvalue ON)
  set(roofit_defvalue ON)

core/gui/src/TGuiFactory.cxx

@@ -56,16 +56,26 @@ TApplicationImp *TGuiFactory::CreateApplicationImp(const char *classname, int *a
 
 TCanvasImp *TGuiFactory::CreateCanvasImp(TCanvas *c, const char *title, UInt_t width, UInt_t height)
 {
+   TString canvName;
    if (gROOT->IsWebDisplay()) {
-      auto ph = gROOT->GetPluginManager()->FindHandler("TCanvasImp", "TWebCanvas");
+      canvName = "TWebCanvas";
+   } else {
+      canvName = gEnv->GetValue("Canvas.Name", "");
+      // in batch web display should be configured explicitely
+      if (canvName == "TWebCanvas")
+         canvName.Clear();
+   }
+
+   if (!canvName.IsNull() && (canvName != "TRootCanvas") && (canvName != "TCanvasImp")) {
+      auto ph = gROOT->GetPluginManager()->FindHandler("TCanvasImp", canvName);
 
       if (ph && ph->LoadPlugin() != -1) {
          auto imp = (TCanvasImp *)ph->ExecPlugin(6, c, title, 0, 0, width, height);
          if (imp)
             return imp;
       }
 
-      Error("CreateCanvasImp", "Fail to create TWebCanvas, please provide missing libWebGui6 or run 'root --web=off'");
+      Error("CreateCanvasImp", "Fail to create %s canvas implementation", canvName.Data());
    }
 
    return new TCanvasImp(c, title, width, height);
@@ -76,16 +86,26 @@ TCanvasImp *TGuiFactory::CreateCanvasImp(TCanvas *c, const char *title, UInt_t w
 
 TCanvasImp *TGuiFactory::CreateCanvasImp(TCanvas *c, const char *title, Int_t x, Int_t y, UInt_t width, UInt_t height)
 {
+   TString canvName;
    if (gROOT->IsWebDisplay()) {
-      auto ph = gROOT->GetPluginManager()->FindHandler("TCanvasImp", "TWebCanvas");
+      canvName = "TWebCanvas";
+   } else {
+      canvName = gEnv->GetValue("Canvas.Name", "");
+      // in batch web display should be configured explicitely
+      if (canvName == "TWebCanvas")
+         canvName.Clear();
+   }
+
+   if (!canvName.IsNull() && (canvName != "TRootCanvas") && (canvName != "TCanvasImp")) {
+      auto ph = gROOT->GetPluginManager()->FindHandler("TCanvasImp", canvName);
 
       if (ph && ph->LoadPlugin() != -1) {
          auto imp = (TCanvasImp *)ph->ExecPlugin(6, c, title, x, y, width, height);
          if (imp)
             return imp;
       }
 
-      Error("CreateCanvasImp", "Fail to create TWebCanvas, please provide missing libWebGui6 or run 'root --web=off'");
+      Error("CreateCanvasImp", "Fail to create %s canvas implementation", canvName.Data());
    }
 
    return new TCanvasImp(c, title, x, y, width, height);

etc/plugins/TCanvasImp/P020_TQt6Canvas.C

@@ -0,0 +1,5 @@
+void P020_TQt6Canvas()
+{
+   gPluginMgr->AddHandler("TCanvasImp", "TQt6Canvas", "TQt6Canvas",
+      "ROOTQt6Canvas", "NewCanvas(TCanvas *, const char *, Int_t, Int_t, UInt_t, UInt_t)");
+}

etc/plugins/TGuiFactory/P020_TQt6GuiFactory.C

@@ -0,0 +1,5 @@
+void P020_TQt6GuiFactory()
+{
+   gPluginMgr->AddHandler("TGuiFactory", "qt6", "TQt6GuiFactory",
+      "ROOTQt6Canvas", "TQt6GuiFactory()");
+}

gui/CMakeLists.txt

@@ -12,6 +12,10 @@ add_subdirectory(guihtml)
 add_subdirectory(recorder)
 add_subdirectory(treemap)
 
+if(qt6canv)
+  add_subdirectory(qt6canvas)
+endif()
+
 if(webgui)
    if(cefweb)
       add_subdirectory(cefdisplay)

gui/gui/src/TRootGuiFactory.cxx

@@ -78,11 +78,12 @@ TCanvasImp *TRootGuiFactory::CreateCanvasImp(TCanvas *c, const char *title,
                                              UInt_t width, UInt_t height)
 {
    TString canvName = gEnv->GetValue("Canvas.Name", "TWebCanvas");
-   if (canvName == "TWebCanvas") {
-      auto ph = gROOT->GetPluginManager()->FindHandler("TCanvasImp", "TWebCanvas");
+   if (!canvName.IsNull() && (canvName != "TRootCanvas"))  {
+      auto ph = gROOT->GetPluginManager()->FindHandler("TCanvasImp", canvName);
 
       if (ph && ph->LoadPlugin() != -1) {
-         ShowWebCanvasWarning();
+         if (canvName == "TWebCanvas")
+            ShowWebCanvasWarning();
          auto imp = (TCanvasImp *) ph->ExecPlugin(6, c, title, 0, 0, width, height);
          if (imp) return imp;
       }
@@ -98,11 +99,12 @@ TCanvasImp *TRootGuiFactory::CreateCanvasImp(TCanvas *c, const char *title,
                                   Int_t x, Int_t y, UInt_t width, UInt_t height)
 {
    TString canvName = gEnv->GetValue("Canvas.Name", "TWebCanvas");
-   if (canvName == "TWebCanvas") {
-      auto ph = gROOT->GetPluginManager()->FindHandler("TCanvasImp", "TWebCanvas");
+   if (!canvName.IsNull() && (canvName != "TRootCanvas"))  {
+      auto ph = gROOT->GetPluginManager()->FindHandler("TCanvasImp", canvName);
 
       if (ph && ph->LoadPlugin() != -1) {
-         ShowWebCanvasWarning();
+         if (canvName == "TWebCanvas")
+            ShowWebCanvasWarning();
          auto imp = (TCanvasImp *) ph->ExecPlugin(6, c, title, x, y, width, height);
          if (imp) return imp;
       }

gui/qt6canvas/CMakeLists.txt

@@ -0,0 +1,49 @@
+# Copyright (C) 1995-2026, Rene Brun and Fons Rademakers.
+# All rights reserved.
+#
+# For the licensing terms see $ROOTSYS/LICENSE.
+# For the list of contributors see $ROOTSYS/README/CREDITS.
+
+############################################################################
+# CMakeLists.txt file for building ROOT gui/qt6canvas package
+############################################################################
+
+find_package(Qt6 COMPONENTS Core Widgets CONFIG)
+
+if(NOT Qt6_FOUND)
+  if(fail-on-missing)
+    message(FATAL_ERROR "Could NOT find Qt6 with Gui components")
+  else()
+    message(WARNING "Qt6 (Gui) not found, disabling option 'qt6canvas'")
+    set(qt6canv OFF CACHE BOOL "Disabled because Qt6 Gui not found" FORCE)
+    return()
+  endif()
+endif()
+
+
+set(CMAKE_AUTOMOC ON)
+set(CMAKE_AUTORCC ON)
+set(CMAKE_AUTOUIC ON)
+set(CMAKE_INCLUDE_CURRENT_DIR ON)
+
+ROOT_STANDARD_LIBRARY_PACKAGE(ROOTQt6Canvas
+  HEADERS
+    TQt6Canvas.h
+    TQt6PadPainter.h
+    TQt6GuiFactory.h
+  SOURCES
+    src/QCanvasWidget.cpp
+    src/QPaintWidget.cpp
+    src/QRootMethodDialog.cpp
+    src/QRootContextMenu.cpp
+    src/TQt6Canvas.cxx
+    src/TQt6PadPainter.cxx
+    src/TQt6GuiFactory.cxx
+  LIBRARIES
+    Qt6::Widgets
+  DEPENDENCIES
+    Core
+    Gpad
+)
+
+target_include_directories(ROOTQt6Canvas PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/src)

gui/qt6canvas/inc/LinkDef.h

@@ -0,0 +1,21 @@
+// Author: Sergey Linev, GSI   26/06/2026
+
+/*************************************************************************
+ * Copyright (C) 1995-2026, Rene Brun and Fons Rademakers.               *
+ * All rights reserved.                                                  *
+ *                                                                       *
+ * For the licensing terms see $ROOTSYS/LICENSE.                         *
+ * For the list of contributors see $ROOTSYS/README/CREDITS.             *
+ *************************************************************************/
+
+#ifdef __CLING__
+
+#pragma link off all globals;
+#pragma link off all classes;
+#pragma link off all functions;
+
+#pragma link C++ class TQt6Canvas+;
+#pragma link C++ class TQt6PadPainter+;
+#pragma link C++ class TQt6GuiFactory+;
+
+#endif

gui/qt6canvas/inc/TQt6Canvas.h

@@ -0,0 +1,83 @@
+// Author: Sergey Linev, GSI   26/06/2026
+
+/*************************************************************************
+ * Copyright (C) 1995-2026, Rene Brun and Fons Rademakers.               *
+ * All rights reserved.                                                  *
+ *                                                                       *
+ * For the licensing terms see $ROOTSYS/LICENSE.                         *
+ * For the list of contributors see $ROOTSYS/README/CREDITS.             *
+ *************************************************************************/
+
+#ifndef ROOT_TQt6Canvas
+#define ROOT_TQt6Canvas
+
+#include "TCanvasImp.h"
+
+class TPad;
+class TExec;
+class QWidget;
+class QCanvasWidget;
+class QPaintWidget;
+
+class TQt6Canvas : public TCanvasImp {
+
+protected:
+
+   QCanvasWidget *fCanvasWidget = nullptr;
+   QPaintWidget *fPaintWidget = nullptr;
+
+   Bool_t fFixedSize = kFALSE;      ///<! true when fixed-size canvas is configured
+   UInt_t fClientBits = 0;          ///<! latest status bits from client like editor visible or not
+
+   void ProcessExecs(TPad *pad, TExec *extra = nullptr);
+
+   Bool_t PerformUpdate(Bool_t async) override;
+   TVirtualPadPainter *CreatePadPainter() override;
+
+   void AssignStatusBits(UInt_t bits);
+
+
+public:
+   TQt6Canvas(TCanvas *c, const char *name, Int_t x, Int_t y, UInt_t width, UInt_t height);
+   ~TQt6Canvas() override;
+
+   QPaintWidget *GetPaintWidget() const { return fPaintWidget; }
+
+   Int_t InitWindow() override;
+   void Close() override;
+   void Show() override;
+
+   UInt_t GetWindowGeometry(Int_t &x, Int_t &y, UInt_t &w, UInt_t &h) override;
+   void GetCanvasGeometry(Int_t wid, UInt_t &w, UInt_t &h) override;
+   void ResizeCanvasWindow(Int_t) override {}
+   void UpdateDisplay(Int_t = 0, Bool_t = kFALSE) override {}
+
+   void ShowMenuBar(Bool_t = kTRUE) override { }
+   void ShowStatusBar(Bool_t = kTRUE) override { }
+   void ShowEditor(Bool_t = kTRUE) override {  }
+   void ShowToolBar(Bool_t = kTRUE) override { }
+   void ShowToolTips(Bool_t  = kTRUE) override { }
+
+   void ForceUpdate() override;
+
+   void SetWindowPosition(Int_t x, Int_t y) override;
+   void SetWindowSize(UInt_t w, UInt_t h) override;
+   void SetWindowTitle(const char *newTitle) override;
+   void SetCanvasSize(UInt_t w, UInt_t h) override;
+   void Iconify() override;
+   void RaiseWindow() override;
+
+   Bool_t HasEditor() const override;
+   Bool_t HasMenuBar() const override;
+   Bool_t HasStatusBar() const override;
+   Bool_t HasToolBar() const override { return kFALSE; }
+   Bool_t HasToolTips() const override;
+
+   static TCanvasImp *NewCanvas(TCanvas *c, const char *name, Int_t x, Int_t y, UInt_t width, UInt_t height);
+
+   static TCanvas *CreateQt6Canvas(const char *name, const char *title, UInt_t width = 1200, UInt_t height = 800);
+
+   ClassDefOverride(TQt6Canvas, 0) // Qt6 implementation for TCanvasImp
+};
+
+#endif

gui/qt6canvas/inc/TQt6ContextMenu.h

@@ -0,0 +1,37 @@
+// Author: Sergey Linev   2/07/2026
+
+/*************************************************************************
+ * Copyright (C) 1995-2026, Rene Brun and Fons Rademakers.               *
+ * All rights reserved.                                                  *
+ *                                                                       *
+ * For the licensing terms see $ROOTSYS/LICENSE.                         *
+ * For the list of contributors see $ROOTSYS/README/CREDITS.             *
+ *************************************************************************/
+
+#ifndef ROOT_QRootContextMenu
+#define ROOT_QRootContextMenu
+
+#include "TContextMenuImp.h"
+#include "TObject.h"
+
+class QRootContextMenu : public TObject, public TContextMenuImp {
+
+private:
+
+   QRootContextMenu(const QRootContextMenu&) = delete;
+   QRootContextMenu& operator=(const QRootContextMenu&)  = delete;
+
+public:
+   QRootContextMenu(TContextMenu *c = nullptr, const char *name = "ROOT Context Menu");
+   ~QRootContextMenu() override;
+
+   void   DisplayPopup(Int_t x, Int_t y) override;
+   void   Dialog(TObject *object, TMethod *method) override;
+   void   Dialog(TObject *object, TFunction *function) override;
+
+   void   RecursiveRemove(TObject *obj) override;
+
+   ClassDefOverride(QRootContextMenu,0)  // Qt6 GUI context sensitive popup menu
+};
+
+#endif

gui/qt6canvas/inc/TQt6GuiFactory.h

@@ -0,0 +1,38 @@
+// Author: Sergey Linev   2/07/2026
+
+/*************************************************************************
+ * Copyright (C) 1995-2026, Rene Brun and Fons Rademakers.               *
+ * All rights reserved.                                                  *
+ *                                                                       *
+ * For the licensing terms see $ROOTSYS/LICENSE.                         *
+ * For the list of contributors see $ROOTSYS/README/CREDITS.             *
+ *************************************************************************/
+
+
+#ifndef ROOT_TQt6GuiFactory
+#define ROOT_TQt6GuiFactory
+
+
+#include "TGuiFactory.h"
+
+
+class TQt6GuiFactory : public TGuiFactory {
+
+protected:
+   void ShowWebCanvasWarning();
+
+public:
+   TQt6GuiFactory(const char *name = "RootQt6", const char *title = "ROOT Qt6 GUI Factory");
+   ~TQt6GuiFactory() override {}
+
+   TApplicationImp *CreateApplicationImp(const char *classname, int *argc, char **argv) override;
+
+   TCanvasImp *CreateCanvasImp(TCanvas *c, const char *title, UInt_t width, UInt_t height) override;
+   TCanvasImp *CreateCanvasImp(TCanvas *c, const char *title, Int_t x, Int_t y, UInt_t width, UInt_t height) override;
+
+   TContextMenuImp *CreateContextMenuImp(TContextMenu *c, const char *name, const char *title) override;
+
+   ClassDefOverride(TQt6GuiFactory,0)  //Factory for Qt6 GUI components
+};
+
+#endif