CERN · Paramveersingh-S · Jun 30, 2026 · Jun 30, 2026 · Jun 30, 2026 · Jul 1, 2026
diff --git a/.github/workflows/ubuntu.yml b/.github/workflows/ubuntu.yml
@@ -19,18 +19,19 @@ jobs:
           - linux/arm/v6
           - linux/arm/v7
           - linux/arm64
+        gtk4: [ON, OFF]
 
     steps:
     - uses: actions/checkout@v4
 
     - name: dependencies
-      run: sudo apt install --fix-missing cmake gcc gfortran libx11-dev libglu1-mesa-dev libmotif-dev tcsh libxaw7-dev libglew-dev libdlm-dev libgl2ps-dev libpng-dev
+      run: sudo apt install --fix-missing cmake gcc gfortran libx11-dev libglu1-mesa-dev libmotif-dev tcsh libxaw7-dev libglew-dev libdlm-dev libgl2ps-dev libpng-dev libgtk-4-dev
 
     - name: clean
       run: make clean
 
     - name: configure
-      run: make config
+      run: make config OPENPHIGS_OPTS="-DUSE_GTK4=${{ matrix.gtk4 }}"
 
     - name: Build
       run: make build

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
@@ -7,11 +7,21 @@ FIND_PACKAGE(PNG REQUIRED)
 FIND_PACKAGE(OpenGL REQUIRED)
 FIND_PACKAGE(X11 REQUIRED)
 FIND_PACKAGE(XMU REQUIRED)
-FIND_PACKAGE(Motif REQUIRED)
+FIND_PACKAGE(Motif)
 FIND_PACKAGE(GLEW)
 FIND_PACKAGE(epoxy)
 FIND_LIBRARY(MATH_LIBRARY m)
 
+option(USE_GTK4 "Use GTK4 for widgets instead of Motif/Xaw" OFF)
+if (USE_GTK4)
+  FIND_PACKAGE(PkgConfig REQUIRED)
+  pkg_check_modules(GTK4 REQUIRED gtk4)
+else()
+  if(NOT Motif_FOUND)
+    message(FATAL_ERROR "Motif not found but USE_GTK4 is OFF. You must have Motif installed.")
+  endif()
+endif()
+
 if (APPLE)
   set(CMAKE_C_COMPILER gcc)
   set(CMAKE_C_COMPILER_ID GNU)
@@ -50,8 +60,12 @@ add_definitions(-g)
 # add_definitions(-DDEBUGINP)
 #add_definitions(-DDEBUGCL)
 #
-# use Motif widgets rather than Xaw
-add_definitions(-DMOTIF)
+# use Motif or GTK4 widgets rather than Xaw
+if(USE_GTK4)
+  add_definitions(-DGTK4_EXT)
+else()
+  add_definitions(-DMOTIF)
+endif()
 
 # use GLEW or epoxy
 if (USE_GLEW)
@@ -65,15 +79,23 @@ endif()
 # gl2ps
 FIND_PATH(GL2PS_INCLUDE_DIR gl2ps.h)
 FIND_LIBRARY(GL2PS_LIBRARY NAMES gl2ps)
-add_definitions(-DGLEW)
-set (GL_INCLUDES ${GL2PS_INCLUDE_DIR})
+if (GL2PS_INCLUDE_DIR)
+  list(APPEND GL_INCLUDES ${GL2PS_INCLUDE_DIR})
+endif()
 
 message(STATUS "GL Includes=${GL_INCLUDES}")
-include_directories(${X11_INCLUDE_DIR} ${MOTIF_INCLUDE_DIR} ${GL_INCLUDES})
+if (USE_GTK4)
+  include_directories(${X11_INCLUDE_DIR} ${GTK4_INCLUDE_DIRS} ${GL_INCLUDES})
+  SET(CMAKE_C_FLAGS "$ENV{CFLAGS} -DGTK4_EXT -g -O0 -fPIC -Wno-deprecated-non-prototype")
+  SET(CMAKE_CXX_FLAGS "$ENV{CXXFLAGS} -DGTK4_EXT -g -O0 -fPIC -Wno-deprecated-non-prototype")
+  SET(CMAKE_Fortran_FLAGS "$ENV{FFLAGS} -DGTK4_EXT -finit-local-zero -g -O0 -fPIC")
+else()
+  include_directories(${X11_INCLUDE_DIR} ${MOTIF_INCLUDE_DIR} ${GL_INCLUDES})
+  SET(CMAKE_C_FLAGS "$ENV{CFLAGS} -DMOTIF -g -O0 -fPIC -Wno-deprecated-non-prototype")
+  SET(CMAKE_CXX_FLAGS "$ENV{CXXFLAGS} -DMOTIF -g -O0 -fPIC -Wno-deprecated-non-prototype")
+  SET(CMAKE_Fortran_FLAGS "$ENV{FFLAGS} -DMOTIF -finit-local-zero -g -O0 -fPIC")
+endif()
 
-SET(CMAKE_C_FLAGS  "$ENV{CFLAGS} -DMOTIF -g -O0 -fPIC -Wno-deprecated-non-prototype")
-SET(CMAKE_CXX_FLAGS "$ENV{CXXFLAGS} -DMOTIF -g -O0  -fPIC -Wno-deprecated-non-prototype")
-SET(CMAKE_Fortran_FLAGS "$ENV{FFLAGS} -DMOTIF -finit-local-zero -g -O0 -fPIC")
 
 SET(CMAKE_EXE_LINKER_FLAGS $ENV{LDFLAGS})
 if (OPENPHIGS_FORCE_32)
@@ -98,11 +120,17 @@ INCLUDE_DIRECTORIES(
     set (XLIBS "")
 endif()
 
+if (USE_GTK4)
+  set(UI_LIBRARIES ${GTK4_LIBRARIES})
+else()
+  set(UI_LIBRARIES ${MOTIF_LIBRARIES})
+endif()
+
 if (USE_GLEW)
   SET(PHIGS_LIBRARIES
       phigs
       ${XLIBS}
-      ${MOTIF_LIBRARIES}
+      ${UI_LIBRARIES}
       ${XMU_LIBRARY}
       ${PNG_LIBRARY}
       ${X11_Xaw_LIB}
@@ -117,7 +145,7 @@ else()
   SET(PHIGS_LIBRARIES
       phigs
       ${XLIBS}
-      ${MOTIF_LIBRARIES}
+      ${UI_LIBRARIES}
       ${XMU_LIBRARY}
       ${PNG_LIBRARY}
       ${X11_Xaw_LIB}

diff --git a/src/include/phigs/private/wsglP.h b/src/include/phigs/private/wsglP.h
@@ -197,6 +197,17 @@ extern "C" {
    */
   void wsgl_clear_geometry();
 
+  /*******************************************************************************
+  /*******************************************************************************
+   * wsgl_set_transparency_pass
+   *
+   * DESCR:       Set the transparency pass and update HLHSR depth mask.
+   * RETURNS:     N/A
+   */
+  void wsgl_set_transparency_pass(Ws *ws, int pass);
+
+  extern int wsgl_current_transparency_pass;
+
   /*******************************************************************************
    * wsgl_init
    *

diff --git a/src/include/phigs/sin.h b/src/include/phigs/sin.h
@@ -51,7 +51,22 @@ SOFTWARE.
 
 #include <sys/types.h>
 #include <X11/Xlib.h>
+#ifdef GTK4_EXT
+#include <gtk/gtk.h>
+#ifndef OPENPHIGS_GTK4_TYPES_DEFINED
+#define OPENPHIGS_GTK4_TYPES_DEFINED
+typedef void* XtAppContext;
+typedef GtkWidget* Widget;
+typedef void* XtPointer;
+typedef unsigned int Cardinal;
+typedef char* String;
+typedef void* Arg;
+typedef void* ArgList;
+typedef unsigned long XtArgVal;
+#endif
+#else
 #include <X11/Intrinsic.h>
+#endif
 
 #include "phigs.h"
 #include "ws_type.h"
@@ -391,8 +406,10 @@ extern void             phg_sin_sample();
   */
 
 /* Xt action procs for input. */
+#ifndef GTK4_EXT
   extern XtActionProc     phg_sin_xt_request_satisfied(Widget);
   extern XtActionProc     phg_sin_xt_string_event(Widget, XEvent*, String *, Cardinal*);
+#endif
 
 #define SIN_CLASS_INDEX(_class) \
     ((int)(_class))

diff --git a/src/include/phigs/ws.h b/src/include/phigs/ws.h
@@ -51,7 +51,22 @@ SOFTWARE.
 
 #include <stdio.h>
 #include <X11/Xlib.h>
+#ifdef GTK4_EXT
+#include <gtk/gtk.h>
+#ifndef OPENPHIGS_GTK4_TYPES_DEFINED
+#define OPENPHIGS_GTK4_TYPES_DEFINED
+typedef void* XtAppContext;
+typedef GtkWidget* Widget;
+typedef void* XtPointer;
+typedef unsigned int Cardinal;
+typedef char* String;
+typedef void* Arg;
+typedef void* ArgList;
+typedef unsigned long XtArgVal;
+#endif
+#else
 #include <X11/Intrinsic.h>
+#endif
 #include <GL/glx.h>
 
 #include "phigs.h"

diff --git a/src/libphigs/cp/cpm_tlkt.c b/src/libphigs/cp/cpm_tlkt.c
@@ -48,12 +48,17 @@ SOFTWARE.
 
 ******************************************************************/
 #include <stdio.h>
+#ifndef GTK4_EXT
 #include <X11/StringDefs.h>
+#ifndef GTK4_EXT
 #include <X11/Shell.h>
+#endif
+#endif
 #include "phg.h"
 #include "ws.h"
 #include "sin.h"
 
+#ifndef GTK4_EXT
 /* TODO: Fill in the real options. */
 static XrmOptionDescRec options[] = {
 {"-horiz",	"scrollbar.orientation", XrmoptionNoArg,  "horizontal"}
@@ -300,15 +305,19 @@ static XtActionsRec	actions[] = {
 };
 
 XContext        phg_sin_device_context_id;
+#endif
 
 /* No need for a "destroy_toolkit function since all the resources are
  * destroyed when the PM terminates.
  */
 
 XtAppContext phg_cpm_init_toolkit( int argc, char **argv )
 {
-  XtAppContext app_con;
+  XtAppContext app_con = NULL;
 
+#ifdef GTK4_EXT
+  gtk_init();
+#else
   XtToolkitInitialize();
 #ifdef DEBUGINP
   printf("Initialising Xt Toolkit\n");
@@ -321,27 +330,36 @@ XtAppContext phg_cpm_init_toolkit( int argc, char **argv )
     XtAppAddActions( app_con, actions, XtNumber(actions) );
     phg_sin_device_context_id = XUniqueContext();
   }
+#endif
   return app_con;
 }
 
 Widget phg_cpm_toolkit_add_connection( XtAppContext context, Display* display, Pint* err )
 {
   int    argc = 0, status = 0;
   char   **argv = (char **)NULL;
-  Widget top_level;
+  Widget top_level = NULL;
 
+  *err = 0;
+#ifdef GTK4_EXT
+  /* In GTK4, Display connection is handled by gtk_init() or implicitly. */
+  /* We can create a dummy or invisible top-level window if needed, but 
+   * OpenPHIGS handles GLX on X11 windows directly. We just need to return 
+   * a valid pointer to indicate success if the caller checks it. */
+  top_level = (Widget)gtk_window_new();
+#else
   /* TODO: XtDisplayInitialize destroys the arg vector, but we need to
    * keep it for the next display initialized.  So copy it to scratch
    * space then pass the copy.
    */
-  *err = 0;
   XtDisplayInitialize( context, display,
         "Workstation", NULL, NULL, 0,
         &argc, argv );
   top_level = XtVaAppCreateShell( NULL, NULL, applicationShellWidgetClass,
 				  display, NULL );
   if (top_level == NULL)
     *err = ERRN204;
+#endif
   return top_level;
 }
 
@@ -354,16 +372,30 @@ int phg_cpm_toolkit_open_ws( Ws *ws ) {
 #endif
     status = 0;
     sprintf( buf, "workstation%d", ws->id );
+#ifdef GTK4_EXT
+    ws->shell = (Widget)gtk_window_new();
+    if (ws->shell == NULL){
+      status = 1;
+    }
+#else
     ws->shell = XtVaCreatePopupShell( buf, applicationShellWidgetClass,
 				      ws->top_level, NULL);
     if (ws->shell == NULL){
       printf("Failed to create shell for %s! Top_level was %ld\n", buf, (long)ws->top_level);
       status = 1;
     }
+#endif
 
     return status;
 }
 
 void phg_cpm_toolkit_close_ws( Ws *ws ) {
+#ifdef GTK4_EXT
+    if (ws->shell) {
+      gtk_window_destroy(GTK_WINDOW(ws->shell));
+      ws->shell = NULL;
+    }
+#else
     XtDestroyWidget( ws->shell );
+#endif
 }
diff --git a/src/libphigs/input/sin_cho.c b/src/libphigs/input/sin_cho.c
@@ -59,17 +59,21 @@ SOFTWARE.
 #include "sin.h"
 #include "private/sinP.h"
 
+#ifndef GTK4_EXT
 #include <X11/StringDefs.h>
 #include <X11/Shell.h>
+#endif
 #ifdef MOTIF
 #include <stdbool.h>
 #include <Xm/Frame.h>
 #include <Xm/ToggleB.h>
 #include <Xm/RowColumn.h>
 #else
+#ifndef GTK4_EXT
 #include <X11/Xaw/Viewport.h>
 #include <X11/Xaw/List.h>
 #endif
+#endif
 /*******************************************************************************
  * choice_notify
  *
@@ -167,7 +171,19 @@ static void enable_choice(
     sprintf( buf, "choice%d", device->num );
     sprintf( title, "Options:");
     /* Create the containing shell. */
-#ifdef MOTIF
+#ifdef GTK4_EXT
+    if (device->item_handle.choice.shell) {
+        gtk_window_destroy(GTK_WINDOW(device->item_handle.choice.shell));
+        device->item_handle.choice.shell = NULL;
+    }
+    device->item_handle.choice.shell = (Widget)gtk_window_new();
+    gtk_window_set_title(GTK_WINDOW(device->item_handle.choice.shell), title);
+    GtkWidget *box = gtk_box_new(GTK_ORIENTATION_VERTICAL, 5);
+    gtk_window_set_child(GTK_WINDOW(device->item_handle.choice.shell), box);
+    device->item_handle.choice.list = (Widget)gtk_list_box_new();
+    gtk_box_append(GTK_BOX(box), (GtkWidget*)device->item_handle.choice.list);
+    w = device->item_handle.choice.list;
+#elif defined(MOTIF)
     device->item_handle.choice.shell =
       XtVaCreatePopupShell( buf, applicationShellWidgetClass,
 			    parent,
@@ -230,10 +246,14 @@ static void enable_choice(
 	XtNcallback, choice_notify, (XtPointer)device );
 #endif
 
+#ifdef GTK4_EXT
+    gtk_window_present(GTK_WINDOW(device->item_handle.choice.shell));
+#else
     XtPopup( device->item_handle.choice.shell, XtGrabNone );
     if ( device->mode == SIN_REQUEST_PENDING )
 	XSaveContext( XtDisplay(w), XtWindow(w), phg_sin_device_context_id,
 	    (caddr_t)device );
+#endif
 #ifdef DEBUGINP
     printf("Enabling choice finished\n");
 #endif