From 2f18ccbffee237845c0b3c2d745d20ac66748f8a Mon Sep 17 00:00:00 2001
From: Olivier Fourdan <ofourdan@redhat.com>
Date: Fri, 27 Jun 2025 12:11:41 +0200
Subject: [PATCH 2/2] Xm/Screen: Add _GTK_WORKAREAS support for multi-monitor

Add support for the GTK property _GTK_WORKAREAS to prevent Motif from
placing its widgets outside of the geometry advertised by the window
manager on a multi-monitor setup.

Unlike the extended window manager hint _NET_WORKAREA which defines a
single rectangle for the whole screen spanning across all the monitors,
_GTK_WORKAREAS provides an area per monitor, making that property more
adequate on a multi-monitor setup.

However, if _GTK_WORKAREAS is not supported, we fallback to the standard
_NET_WORKAREA property.

Support for _GTK_WORKAREAS depends on the Xinerama patches as it shares
the same logic.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
---
 lib/Xm/Screen.c | 92 ++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 91 insertions(+), 1 deletion(-)

diff --git a/lib/Xm/Screen.c b/lib/Xm/Screen.c
index 6269ffb3..d8d24e9a 100644
--- a/lib/Xm/Screen.c
+++ b/lib/Xm/Screen.c
@@ -1554,6 +1554,91 @@ _XmScreenGetCurrentDesktop(Screen *screen)
   return desktop;
 }
 
+static Boolean
+_XmCheckGtkWorkareas(
+        Screen *screen,
+	Position pt_x,
+	Position pt_y,
+	Position *ret_x,
+	Position *ret_y,
+	Position *ret_max_x,
+	Position *ret_max_y )
+{
+    Atom          XmA_GTK_WORKAREAS;
+    Atom          type;
+    Display       *dpy;
+    Window        rootwindow;
+    int           result = False;
+    int           desktop = 0;
+    int           format;
+    unsigned long lengthRtn;
+    unsigned long bytesAfter;
+    unsigned char *data;
+    long          *gtk_workareas;
+    char          atom_name[32];
+    int           monitor, n_monitors;
+    Position      tmp_x, tmp_y;
+    Position      tmp_max_x, tmp_max_y;
+    Boolean       ret = False;
+
+    dpy = DisplayOfScreen(screen);
+    rootwindow = RootWindowOfScreen(screen);
+    desktop = _XmScreenGetCurrentDesktop(screen);
+
+    snprintf(atom_name, sizeof(atom_name), "_GTK_WORKAREAS_D%d", desktop);
+    XmA_GTK_WORKAREAS = XInternAtom(dpy, atom_name, False);
+
+    result = XGetWindowProperty(dpy, rootwindow,
+                                XmA_GTK_WORKAREAS,
+                                0L, 100000L, False, XA_CARDINAL,
+                                &type, &format, &lengthRtn, &bytesAfter,
+                                &data);
+
+    if (result != Success || type != XA_CARDINAL || format != 32 ||
+      bytesAfter != 0 || lengthRtn % 4 != 0) {
+      goto done;
+    }
+
+    gtk_workareas = (long *) data;
+    n_monitors = lengthRtn / 4;
+
+#define GTK_WORKAREA_X (monitor * 4)
+#define GTK_WORKAREA_Y (monitor * 4 + 1)
+#define GTK_WORKAREA_WIDTH (monitor * 4 + 2)
+#define GTK_WORKAREA_HEIGHT (monitor * 4 + 3)
+
+    for (monitor = 0; monitor < n_monitors; ++monitor) {
+      tmp_x = gtk_workareas[GTK_WORKAREA_X];
+      tmp_y = gtk_workareas[GTK_WORKAREA_Y];
+      tmp_max_x = tmp_x + gtk_workareas[GTK_WORKAREA_WIDTH];
+      tmp_max_y = tmp_y + gtk_workareas[GTK_WORKAREA_HEIGHT];
+
+      if (pt_x >= tmp_x && pt_x < tmp_max_x && pt_y >= tmp_y && pt_y < tmp_max_y) {
+        *ret_x = tmp_x;
+        *ret_y = tmp_y;
+        *ret_max_x = tmp_max_x;
+        *ret_max_y = tmp_max_y;
+        ret = True;
+        break; /* We have a match */
+      }
+    }
+
+#undef GTK_WORKAREA_X
+#undef GTK_WORKAREA_Y
+#undef GTK_WORKAREA_WIDTH
+#undef GTK_WORKAREA_HEIGHT
+
+#ifdef DEBUG_XINERAMA
+    printf("Point (%i,%i) constrained by _GTK_WORKAREAS_D%d within (%i,%i) and (%i,%i)\n",
+           pt_x, pt_y, desktop, *ret_x, *ret_y, *ret_max_x, *ret_max_y);
+#endif /* DEBUG_XINERAMA */
+
+done:
+    if (data)
+        XFree(data);
+    return ret;
+}
+
 static void
 _XmCheckNetWorkarea(
         Screen *screen,
@@ -1637,6 +1722,7 @@ _XmScreenGetBoundariesAtpoint(
     XmDisplay	xmDisplay;
     Position screen_x, screen_y;
     Position screen_max_x, screen_max_y;
+    Boolean check_gtk_workarea;
 #ifdef HAVE_LIBXINERAMA
     Position tmp_x, tmp_y;
     Position tmp_max_x, tmp_max_y;
@@ -1668,7 +1754,11 @@ _XmScreenGetBoundariesAtpoint(
       }
     }
 #endif /* HAVE_LIBXINERAMA */
-    _XmCheckNetWorkarea(screen, &screen_x, &screen_y, &screen_max_x, &screen_max_y);
+    check_gtk_workarea = _XmCheckGtkWorkareas(screen, pt_x, pt_y,
+                                              &screen_x, &screen_y,
+                                              &screen_max_x, &screen_max_y);
+    if (!check_gtk_workarea)
+      _XmCheckNetWorkarea(screen, &screen_x, &screen_y, &screen_max_x, &screen_max_y);
 out:
 #ifdef DEBUG_XINERAMA
     printf("Point (%i,%i) constrained within (%i,%i) and (%i,%i)\n",
-- 
2.50.0