[webgui] support headless CEF on Linux and Windows

documentation/doxygen/Doxyfile

@@ -1123,7 +1123,6 @@ EXCLUDE_PATTERNS       = */G__* \
                          *.xml \
                          *.dtd \
                          */graf3d/eve7/glu/* \
-                         */gui/cefdisplay/* \
                          */gui/qt6webdisplay/* \
                          */tutorials/visualisation/webgui/qtweb/* \
                          */math/mathcore/src/CDT*

gui/cefdisplay/CMakeLists.txt

@@ -55,7 +55,7 @@ set(CEF_MAIN src/cef_main.cxx)
 
 ROOT_LINKER_LIBRARY(${libname} ${CEF_sources} ${CEF_platform}
                     LIBRARIES ${CMAKE_DL_LIBS} ${CEF_LIBRARY} ${CEF_DLL_WRAPPER} ${CEF_LIB_DEPENDENCY}
-                    DEPENDENCIES RHTTP ROOTWebDisplay)
+                    DEPENDENCIES RHTTP ASImage ROOTWebDisplay)
 
 target_compile_definitions(${libname} PRIVATE NDEBUG)
 

gui/cefdisplay/Readme.md

@@ -4,17 +4,16 @@
 
 See details about [Chromium Embedded Framework](https://bitbucket.org/chromiumembedded/cef)
 
-1. Current code tested with CEF3 branch 6998, Chromium 134 (April 2025)
-   Some older CEF versions (like 107 or 124) may also be supported.
+1. Current code tested with CEF3 branch 778, Chromium 148 (June 2026)
 
 2. Download binary code from [https://cef-builds.spotifycdn.com/index.html](https://cef-builds.spotifycdn.com/index.html)
    and unpack it in directory without spaces and special symbols:
 
 ~~~
      $ mkdir /d/cef
      $ cd /d/cef/
-     $ wget https://cef-builds.spotifycdn.com/cef_binary_134.3.9%2Bg5dc6f2f%2Bchromium-134.0.6998.178_linux64_minimal.tar.bz2
-     $ tar xjf cef_binary_134.3.9+g5dc6f2f+chromium-134.0.6998.178_linux64_minimal.tar.bz2
+     $ wget https://cef-builds.spotifycdn.com/cef_binary_148.0.10%2Bg7ee53f5%2Bchromium-148.0.7778.218_linux64.tar.bz2
+     $ tar xjf cef_binary_148.0.10+g7ee53f5+chromium-148.0.7778.218_linux64.tar.bz2
 ~~~
 
 
@@ -24,7 +23,7 @@ See details about [Chromium Embedded Framework](https://bitbucket.org/chromiumem
 4. Compile CEF to produce `libcef_dll_wrapper`:
 
 ~~~
-     $ cd cef_binary_134.3.9+g5dc6f2f+chromium-134.0.6998.178_linux64_minimal
+     $ cd xjf cef_binary_148.0.10+g7ee53f5+chromium-148.0.7778.218_linux64
      $ mkdir build
      $ cd build
      $ cmake ..
@@ -34,13 +33,10 @@ See details about [Chromium Embedded Framework](https://bitbucket.org/chromiumem
 5. Set CEF_ROOT variable to unpacked directory:
 
 ~~~
-     $ export CEF_ROOT=/d/cef/cef_binary_134.3.9+g5dc6f2f+chromium-134.0.6998.178_linux64_minimal
+     $ export CEF_ROOT=/d/cef/xjf cef_binary_148.0.10+g7ee53f5+chromium-148.0.7778.218_linux64
 ~~~
 
-6. When configure ROOT compilation with `cmake -Dwebgui=ON -Dcefweb=ON ...`, CEF_ROOT shell variable should be set appropriately.
-   During compilation library `$ROOTSYS/lib/libROOTCefDisplay.so` and executable `$ROOTSYS/bin/cef_main`
-   should be created. Also check that several files like `icudtl.dat`, `v8_context_snapshot_blob.bin`, `snapshot_blob.bin`
-   copied into ROOT library directory
+6. When configure ROOT compilation with `cmake -Dwebgui=ON -Dcefweb=ON ...`, CEF_ROOT shell variable should be set appropriately. During compilation library `$ROOTSYS/lib/libROOTCefDisplay.so` and executable `$ROOTSYS/bin/cef_main` should be created. Also check that several files like `icudtl.dat`, `v8_context_snapshot_blob.bin`, `snapshot_blob.bin` copied into ROOT library directory
 
 7. Run ROOT with `--web=cef` argument to use CEF web display like:
 
@@ -51,7 +47,7 @@ See details about [Chromium Embedded Framework](https://bitbucket.org/chromiumem
 
 ## Compile libcef_dll_wrapper on Windows
 
-1. Download binary win32 build like https://cef-builds.spotifycdn.com/cef_binary_95.7.12%2Bg99c4ac0%2Bchromium-95.0.4638.54_windows32.tar.bz2
+1. Download binary win32 build like [win64](https://cef-builds.spotifycdn.com/cef_binary_148.0.10%2Bg7ee53f5%2Bchromium-148.0.7778.218_windows64.tar.bz2)
 
 2. Extract in directory without spaces like `C:\Soft\cef`
 
@@ -62,45 +58,18 @@ See details about [Chromium Embedded Framework](https://bitbucket.org/chromiumem
    $ cd C:\Soft\cef
    $ mkdir build
    $ cd build
-   $ cmake -G"Visual Studio 16 2019" -A Win32 -Thost=x64 ..
+   $ cmake ..
    $ cmake --build . --config Release --target libcef_dll_wrapper
 ~~~
 
 5. Before compiling ROOT, `set CEF_ROOT=C:\Soft\cef` variable
 
 
-## Using plain CEF in ROOT batch mode on Linux
+## Using plain CEF in ROOT batch mode on Linux and Windows
 
-Default CEF builds, provided by [https://cef-builds.spotifycdn.com/index.html](https://cef-builds.spotifycdn.com/index.html), do
-not include support of Ozone framework, which the only support headless mode in CEF. To run ROOT in headless (or batch) made with such CEF distribution,
-one can use `Xvfb` server. Most simple way is to use `xvfb-run` utility like:
+Default CEF builds, provided by [https://cef-builds.spotifycdn.com/index.html](https://cef-builds.spotifycdn.com/index.html), now (June 2026) **INCLUDES!** support of Ozone framework, which allows to run CEF in headless mode on Linux and Windows. So one can run different ROOT macros and tests in batch mode like
 
 ~~~
-      $ xvfb-run --server-args='-screen 0, 1024x768x16'  root.exe --web=cef $ROOTSYS/tutorials/experimental/rcanvas/rline.cxx -q
+      $ cd $ROOTSYS/test
+      $ ./stressGraphics -b --web=cef
 ~~~
-
-Or run `Xvfb` before starting ROOT:
-
-~~~
-     $ Xvfb :99 &
-     $ export DISPLAY=:99
-     $ root.exe --web=cef $ROOTSYS/tutorials/experimental/rcanvas/rline.cxx -q
-~~~
-
-
-## Compile CEF with ozone support
-
-Since March 2019 one can compile [CEF without X11](https://bitbucket.org/chromiumembedded/cef/issues/2296/), but such builds not provided.
-Therefore to be able to use real headless mode in CEF, one should compile it from sources.
-On [CEF build tutorial](https://bitbucket.org/chromiumembedded/cef/wiki/AutomatedBuildSetup.md) one can find complete compilation documentation.
-Several Ubuntu distributions are supported by CEF, all others may require extra work. Once all depndencies are installed, CEF with ozone support can be compiled with following commands:
-
-~~~
-   $ export GN_DEFINES="is_official_build=true use_sysroot=true use_allocator=none symbol_level=1 is_cfi=false use_thin_lto=false use_ozone=true"
-   $ python automate-git.py --download-dir=/home/user/cef --branch=4638 --minimal-distrib --client-distrib --force-clean --x64-build --build-target=cefsimple
-~~~
-
-With little luck one get prepared tarballs in `/home/user/cef/chromium/src/cef/binary_distrib`.
-Just install it in the same way as described before in this document.
-ROOT will automatically detect that CEF build with `ozone` support and will use it for both interactive and headless modes.
-

gui/cefdisplay/inc/gui_handler.h

@@ -109,7 +109,7 @@ class GuiHandler : public CefClient,
 
    std::string MakePageUrl(THttpServer *serv, const std::string &addr);
 
-   static bool PlatformInit();
+   static void PlatformInit();
 
    static std::string GetDataURI(const std::string& data, const std::string& mime_type);
 

gui/cefdisplay/inc/simple_app.h

@@ -35,22 +35,24 @@ class SimpleApp : public CefApp,
                   /*, public CefRenderProcessHandler */
                   public CefBrowserProcessHandler {
 protected:
-   bool fUseViewes{false};  ///<! is views framework used
+   bool fUseViewes = false;  ///<! is views framework used
+   bool fSupressLog = false; ///<! supress log output when possible
    THttpServer *fFirstServer; ///<! first server
    std::string fFirstUrl;   ///<! first URL to open
    std::string fFirstContent; ///<! first page content open
    CefRect fFirstRect;      ///<! original width
    bool fFirstHeadless{false}; ///<! is first window is headless
    RCefWebDisplayHandle *fNextHandle{nullptr}; ///< next handle where browser will be created
+   bool fNextHeadless = false; ///< if next handle display is headless
 
    CefRefPtr<GuiHandler> fGuiHandler; ///<! normal handler
 
 public:
-   SimpleApp(bool use_viewes,
+   SimpleApp(bool use_viewes, bool supress_log,
              THttpServer *serv = nullptr, const std::string &url = "", const std::string &cont = "",
              int width = 0, int height = 0, bool headless = false);
 
-   void SetNextHandle(RCefWebDisplayHandle *handle);
+   void SetNextHandle(RCefWebDisplayHandle *handle, bool headless);
 
    // CefApp methods:
    CefRefPtr<CefBrowserProcessHandler> GetBrowserProcessHandler() override { return this; }

gui/cefdisplay/src/RCefWebDisplayHandle.cxx

@@ -87,47 +87,88 @@ std::unique_ptr<ROOT::RWebDisplayHandle> RCefWebDisplayHandle::CefCreator::Displ
    if (!args.IsStandalone())
       handle->fCloseBrowser = false;
 
+   Int_t wait_tmout = args.IsHeadless() ? gEnv->GetValue("WebGui.CefHeadlessTimeout", 30) : -1;
+
    if (fCefApp) {
-      fCefApp->SetNextHandle(handle.get());
+      fCefApp->SetNextHandle(handle.get(), args.IsHeadless());
 
       CefRect rect((args.GetX() > 0) ? args.GetX() : 0, (args.GetY() > 0) ? args.GetY() : 0,
             (args.GetWidth() > 0) ? args.GetWidth() : 800, (args.GetHeight() > 0) ? args.GetHeight() : 600);
 
       fCefApp->StartWindow(args.GetHttpServer(), args.GetFullUrl(), args.GetPageContent(), rect);
 
       if (args.IsHeadless())
-         handle->WaitForContent(30, args.GetExtraArgs()); // 30 seconds
+         handle->WaitForContent(wait_tmout, args.GetExtraArgs());
 
       return handle;
    }
 
-   bool use_views = GuiHandler::PlatformInit();
+   GuiHandler::PlatformInit();
+   bool use_views = true;
 
    TString env_use_views = gEnv->GetValue("WebGui.CefUseViews", "");
    if ((env_use_views == "yes") || (env_use_views == "1"))
       use_views = true;
    else if ((env_use_views == "no") || (env_use_views == "0"))
       use_views = false;
 
+   // Specify CEF global settings here.
+   CefSettings settings;
+
+   TString ceflog = gEnv->GetValue("WebGui.CefLogSeveriry", "fatal");
+   if (ceflog == "fatal")
+      settings.log_severity = LOGSEVERITY_FATAL;
+   else if (ceflog == "verbose")
+      settings.log_severity = LOGSEVERITY_VERBOSE;
+   else if (ceflog == "info")
+      settings.log_severity = LOGSEVERITY_INFO;
+   else if (ceflog == "warning")
+      settings.log_severity = LOGSEVERITY_WARNING;
+   else if (ceflog == "error")
+      settings.log_severity = LOGSEVERITY_ERROR;
+   else if (ceflog == "disable")
+      settings.log_severity = LOGSEVERITY_DISABLE;
+   else
+      settings.log_severity = LOGSEVERITY_FATAL;
+
+   bool supress_log = (settings.log_severity == LOGSEVERITY_DISABLE) ||
+                      (settings.log_severity == LOGSEVERITY_FATAL);
+
+   TApplication *root_app = gROOT->GetApplication();
+
+   std::vector<const char *> cef_argv = { root_app->Argv(0) };
+
 #ifdef OS_WIN
-   CefMainArgs main_args(GetModuleHandle(nullptr));
+
+   CefMainArgs main_args(args.IsHeadless() ? (HINSTANCE) 0 : GetModuleHandle(nullptr));
+
 #else
-   TApplication *root_app = gROOT->GetApplication();
 
-   int cef_argc = 1;
-   const char *arg2 = nullptr, *arg3 = nullptr;
    if (args.IsHeadless()) {
-      // arg2 = "--allow-file-access-from-files";
-      arg2 = "--disable-web-security";
-      cef_argc++;
-      if (use_views) {
-         arg3 = "--ozone-platform=headless";
-         cef_argc++;
-      }
+      cef_argv.emplace_back("--user-data-dir=.");
+      cef_argv.emplace_back("--allow-file-access-from-files");
+      cef_argv.emplace_back("--disable-web-security");
+      cef_argv.emplace_back("--disable-gpu");
+      cef_argv.emplace_back("--ignore-gpu-blocklist");
+#ifdef OS_LINUX
+      cef_argv.emplace_back("--use-gl=swiftshader");
+      cef_argv.emplace_back("--enable-unsafe-swiftshader");
+#endif
+      cef_argv.emplace_back("--off-screen-rendering-enabled");
+      if (use_views)
+         cef_argv.emplace_back("--ozone-platform=headless");
+   }
+
+   if (supress_log) {
+      cef_argv.emplace_back("--disable-logging");
+      cef_argv.emplace_back("--enable-logging=none");
+      cef_argv.emplace_back("--v=-1");
    }
-   char *cef_argv[] = {root_app->Argv(0), (char *) arg2, (char *) arg3, nullptr};
 
-   CefMainArgs main_args(cef_argc, cef_argv);
+   cef_argv.emplace_back(nullptr);
+
+   CefMainArgs main_args(cef_argv.size() - 1, (char **) cef_argv.data());
+
 #endif
 
    // CEF applications have multiple sub-processes (render, plugin, GPU, etc)
@@ -146,8 +187,6 @@ std::unique_ptr<ROOT::RWebDisplayHandle> RCefWebDisplayHandle::CefCreator::Displ
    //         XSetErrorHandler(XErrorHandlerImpl);
    //         XSetIOErrorHandler(XIOErrorHandlerImpl);
 
-   // Specify CEF global settings here.
-   CefSettings settings;
 
    TString cef_main = TROOT::GetBinDir() + "/cef_main";
    cef_string_ascii_to_utf16(cef_main.Data(), cef_main.Length(), &settings.browser_subprocess_path);
@@ -177,17 +216,15 @@ std::unique_ptr<ROOT::RWebDisplayHandle> RCefWebDisplayHandle::CefCreator::Displ
    settings.no_sandbox = true;
    // if (gROOT->IsWebDisplayBatch()) settings.single_process = true;
 
-   // if (batch_mode)
-   // settings.windowless_rendering_enabled = true;
+   if (args.IsHeadless())
+      settings.windowless_rendering_enabled = true;
 
    // settings.external_message_pump = true;
    // settings.multi_threaded_message_loop = false;
 
    std::string plog = "cef.log";
    cef_string_ascii_to_utf16(plog.c_str(), plog.length(), &settings.log_file);
 
-   settings.log_severity = LOGSEVERITY_ERROR; // LOGSEVERITY_VERBOSE, LOGSEVERITY_INFO, LOGSEVERITY_WARNING,
-   // LOGSEVERITY_ERROR, LOGSEVERITY_DISABLE
    // settings.uncaught_exception_stack_size = 100;
    // settings.ignore_certificate_errors = true;
 
@@ -196,18 +233,19 @@ std::unique_ptr<ROOT::RWebDisplayHandle> RCefWebDisplayHandle::CefCreator::Displ
    // SimpleApp implements application-level callbacks for the browser process.
    // It will create the first browser instance in OnContextInitialized() after
    // CEF has initialized.
-   fCefApp = new SimpleApp(use_views, args.GetHttpServer(), args.GetFullUrl(), args.GetPageContent(),
-                                args.GetWidth() > 0 ? args.GetWidth() : 800,
-                                args.GetHeight() > 0 ? args.GetHeight() : 600,
-                                args.IsHeadless());
+   fCefApp = new SimpleApp(use_views, supress_log,
+                           args.GetHttpServer(), args.GetFullUrl(), args.GetPageContent(),
+                           args.GetWidth() > 0 ? args.GetWidth() : 800,
+                           args.GetHeight() > 0 ? args.GetHeight() : 600,
+                           args.IsHeadless());
 
-   fCefApp->SetNextHandle(handle.get());
+   fCefApp->SetNextHandle(handle.get(), args.IsHeadless());
 
    // Initialize CEF for the browser process.
    CefInitialize(main_args, settings, fCefApp.get(), nullptr);
 
    if (args.IsHeadless()) {
-      handle->WaitForContent(30, args.GetExtraArgs()); // 30 seconds
+      handle->WaitForContent(wait_tmout, args.GetExtraArgs());
    } else {
       // Create timer to let run CEF message loop together with ROOT event loop
       Int_t interval = gEnv->GetValue("WebGui.CefTimer", 10);

gui/cefdisplay/src/gui_handler.cxx

@@ -21,6 +21,7 @@
 
 #include <sstream>
 #include <fstream>
+#include <iostream>
 #include <string>
 
 #include "include/base/cef_bind.h"
@@ -175,21 +176,22 @@ bool GuiHandler::OnConsoleMessage(CefRefPtr<CefBrowser> browser,
    switch (level) {
    case LOGSEVERITY_WARNING:
       if (fConsole > -1)
-         R__LOG_WARNING(CefWebDisplayLog()) << Form("CEF: %s:%d: %s", src.c_str(), line, message.ToString().c_str());
+         std::cout << TString::Format("CEF: %s:%d: %s", src.c_str(), line, message.ToString().c_str()) << std::endl;
       break;
    case LOGSEVERITY_ERROR:
       if (fConsole > -2)
-         R__LOG_ERROR(CefWebDisplayLog()) << Form("CEF: %s:%d: %s", src.c_str(), line, message.ToString().c_str());
+         std::cerr << TString::Format("CEF: %s:%d: %s", src.c_str(), line, message.ToString().c_str()) << std::endl;
       break;
    default:
       if (fConsole > 0)
-         R__LOG_DEBUG(0, CefWebDisplayLog()) << Form("CEF: %s:%d: %s", src.c_str(), line, message.ToString().c_str());
+         std::cout << TString::Format("CEF: %s:%d: %s", src.c_str(), line, message.ToString().c_str()) << std::endl;
       break;
    }
 
    return true;
 }
 
+
 cef_return_value_t GuiHandler::OnBeforeResourceLoad(
     CefRefPtr<CefBrowser> browser,
     CefRefPtr<CefFrame> frame,

gui/cefdisplay/src/gui_handler_linux.cxx

@@ -48,16 +48,10 @@ int x11_errhandler( Display *dpy, XErrorEvent *err )
   return 0;
 }
 
-bool GuiHandler::PlatformInit()
+void GuiHandler::PlatformInit()
 {
    // install custom X11 error handler to avoid application exit in case of X11 failure
    XSetErrorHandler( x11_errhandler );
-
-   #if CEF_VERSION_MAJOR > 130
-   return true; // use CEF view framework
-   #else
-   return false; // do not use CEF view framework
-   #endif
 }
 
 void GuiHandler::PlatformTitleChange(CefRefPtr<CefBrowser> browser, const CefString &title)
@@ -116,9 +110,8 @@ bool GuiHandler::PlatformResize(CefRefPtr<CefBrowser> browser, int width, int he
 
 #else
 
-bool GuiHandler::PlatformInit()
+void GuiHandler::PlatformInit()
 {
-   return true; // use view framework
 }
 
 void GuiHandler::PlatformTitleChange(CefRefPtr<CefBrowser>, const CefString &)

gui/cefdisplay/src/gui_handler_mac.mm

@@ -16,10 +16,8 @@
 
 #include "include/cef_browser.h"
 
-
-bool GuiHandler::PlatformInit()
+void GuiHandler::PlatformInit()
 {
-   return false; // MAC not yet support ozone and headless mode
 }
 
 void GuiHandler::PlatformTitleChange(CefRefPtr<CefBrowser> browser, const CefString &title)