Added setting of _NET_WM_PID.

src/x11_init.c

@@ -410,6 +410,9 @@ static void detectEWMH(void)
     _glfw.x11.NET_WM_ICON_NAME =
         getSupportedAtom(supportedAtoms, atomCount, "_NET_WM_ICON_NAME");
 
+    _glfw.x11.NET_WM_PID =
+        getSupportedAtom(supportedAtoms, atomCount, "_NET_WM_PID");
+
     _glfw.x11.NET_WM_PING =
         getSupportedAtom(supportedAtoms, atomCount, "_NET_WM_PING");
 

src/x11_platform.h

@@ -112,6 +112,7 @@ typedef struct _GLFWlibraryX11
     Atom            WM_DELETE_WINDOW;
     Atom            NET_WM_NAME;
     Atom            NET_WM_ICON_NAME;
+    Atom            NET_WM_PID;
     Atom            NET_WM_PING;
     Atom            NET_WM_STATE;
     Atom            NET_WM_STATE_FULLSCREEN;

src/x11_window.c

@@ -204,6 +204,16 @@ static GLboolean createWindow(_GLFWwindow* window,
         }
     }
 
+    if (_glfw.x11.NET_WM_PID != None)
+    {
+        const pid_t pid = getpid();
+
+        XChangeProperty(_glfw.x11.display,  window->x11.handle,
+                        _glfw.x11.NET_WM_PID, XA_CARDINAL, 32,
+                        PropModeReplace,
+                        (unsigned char*) &pid, 1);
+    }
+
     // Set ICCCM WM_HINTS property
     {
         XWMHints* hints = XAllocWMHints();