Wayland: Set "class" for each window we create

This will be used by Wayland compositors to match the application ID and
.desktop file to the SDL window(s).

Applications can set the SDL_VIDEO_WAYLAND_WMCLASS environemnt variable
early in the process to override using the binary name as a fallback.

Note that we also support the SDL_VIDEO_X11_WMCLASS in the Wayland
backend so that if a program correctly associated the desktop file with
the window under X11, only a newer SDL would be needed for it to work
under Wayland.

https://bugzilla.libsdl.org/show_bug.cgi?id=3376

src/video/wayland/SDL_waylandvideo.c

@@ -35,6 +35,8 @@
 #include "SDL_waylandmouse.h"
 #include "SDL_waylandtouch.h"
 
+#include <sys/types.h>
+#include <unistd.h>
 #include <fcntl.h>
 #include <xkbcommon/xkbcommon.h>
 
@@ -55,6 +57,56 @@ Wayland_SetDisplayMode(_THIS, SDL_VideoDisplay *display, SDL_DisplayMode *mode);
 static void
 Wayland_VideoQuit(_THIS);
 
+/* Find out what class name we should use
+ * Based on src/video/x11/SDL_x11video.c */
+static char *
+get_classname()
+{
+    char *spot;
+#if defined(__LINUX__) || defined(__FREEBSD__)
+    char procfile[1024];
+    char linkfile[1024];
+    int linksize;
+#endif
+
+    /* First allow environment variable override */
+    spot = SDL_getenv("SDL_VIDEO_WAYLAND_WMCLASS");
+    if (spot) {
+        return SDL_strdup(spot);
+    } else {
+        /* Fallback to the "old" envvar */
+        spot = SDL_getenv("SDL_VIDEO_X11_WMCLASS");
+        if (spot) {
+            return SDL_strdup(spot);
+        }
+    }
+
+    /* Next look at the application's executable name */
+#if defined(__LINUX__) || defined(__FREEBSD__)
+#if defined(__LINUX__)
+    SDL_snprintf(procfile, SDL_arraysize(procfile), "/proc/%d/exe", getpid());
+#elif defined(__FREEBSD__)
+    SDL_snprintf(procfile, SDL_arraysize(procfile), "/proc/%d/file",
+                 getpid());
+#else
+#error Where can we find the executable name?
+#endif
+    linksize = readlink(procfile, linkfile, sizeof(linkfile) - 1);
+    if (linksize > 0) {
+        linkfile[linksize] = '\0';
+        spot = SDL_strrchr(linkfile, '/');
+        if (spot) {
+            return SDL_strdup(spot + 1);
+        } else {
+            return SDL_strdup(linkfile);
+        }
+    }
+#endif /* __LINUX__ || __FREEBSD__ */
+
+    /* Finally use the default we've used forever */
+    return SDL_strdup("SDL_App");
+}
+
 /* Wayland driver bootstrap functions */
 static int
 Wayland_Available(void)
@@ -307,6 +359,9 @@ Wayland_VideoInit(_THIS)
 
     Wayland_InitMouse();
 
+    /* Get the surface class name, usually the name of the application */
+    data->classname = get_classname();
+
     WAYLAND_wl_display_flush(data->display);
 
     return 0;
@@ -375,6 +430,7 @@ Wayland_VideoQuit(_THIS)
         WAYLAND_wl_display_disconnect(data->display);
     }
 
+    SDL_free(data->classname);
     free(data);
     _this->driverdata = NULL;
 }

src/video/wayland/SDL_waylandvideo.h

@@ -57,6 +57,8 @@ typedef struct {
     struct qt_surface_extension *surface_extension;
     struct qt_windowmanager *windowmanager;
 #endif /* SDL_VIDEO_DRIVER_WAYLAND_QT_TOUCH */
+
+    char *classname;
 } SDL_VideoData;
 
 #endif /* _SDL_waylandvideo_h */

src/video/wayland/SDL_waylandwindow.c

@@ -178,6 +178,7 @@ int Wayland_CreateWindow(_THIS, SDL_Window *window)
     wl_surface_set_user_data(data->surface, data);
     data->shell_surface = wl_shell_get_shell_surface(c->shell,
                                                      data->surface);
+    wl_shell_surface_set_class (data->shell_surface, c->classname);
 #ifdef SDL_VIDEO_DRIVER_WAYLAND_QT_TOUCH    
     if (c->surface_extension) {
         data->extended_surface = qt_surface_extension_get_extended_surface(