From cd9c25e80065dce4dd5a20b26c858d03e2b37eed Mon Sep 17 00:00:00 2001
From: Sam Lantinga <slouken@libsdl.org>
Date: Fri, 31 May 2024 09:30:37 -0700
Subject: [PATCH] Don't set the borderless flag if we're about to go
 fullscreen.

This prevents the GNOME window manager from moving the window to a different display before the window goes fullscreen.

Fixes https://github.com/libsdl-org/SDL/issues/9915
---
 src/video/SDL_video.c         |  1 +
 src/video/x11/SDL_x11window.c | 13 +++++++++++--
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/src/video/SDL_video.c b/src/video/SDL_video.c
index 1d4911941e..2f22a2f521 100644
--- a/src/video/SDL_video.c
+++ b/src/video/SDL_video.c
@@ -2254,6 +2254,7 @@ SDL_Window *SDL_CreateWindowWithProperties(SDL_PropertiesID props)
         window->y = bounds.y;
         window->w = bounds.w;
         window->h = bounds.h;
+        window->pending_flags |= SDL_WINDOW_FULLSCREEN;
         flags |= SDL_WINDOW_FULLSCREEN;
     }
 
diff --git a/src/video/x11/SDL_x11window.c b/src/video/x11/SDL_x11window.c
index efd36354af..fda1f07812 100644
--- a/src/video/x11/SDL_x11window.c
+++ b/src/video/x11/SDL_x11window.c
@@ -655,8 +655,13 @@ int X11_CreateWindow(SDL_VideoDevice *_this, SDL_Window *window, SDL_PropertiesI
         return SDL_SetError("Couldn't create window");
     }
 
-    SetWindowBordered(display, screen, w,
-                      !(window->flags & SDL_WINDOW_BORDERLESS));
+    /* Don't set the borderless flag if we're about to go fullscreen.
+     * This prevents the window manager from moving a full-screen borderless
+     * window to a different display before we actually go fullscreen.
+     */
+    if (!(window->pending_flags & SDL_WINDOW_FULLSCREEN)) {
+        SetWindowBordered(display, screen, w, !(window->flags & SDL_WINDOW_BORDERLESS));
+    }
 
     sizehints = X11_XAllocSizeHints();
     /* Setup the normal size hints */
@@ -1729,6 +1734,10 @@ static int X11_SetWindowFullscreenViaWM(SDL_VideoDevice *_this, SDL_Window *wind
         X11_SetNetWMState(_this, data->xwindow, flags);
     }
 
+    if ((window->flags & SDL_WINDOW_BORDERLESS) && !fullscreen) {
+        SetWindowBordered(display, displaydata->screen, data->xwindow, SDL_FALSE);
+    }
+
     if (data->visual->class == DirectColor) {
         if (fullscreen) {
             X11_XInstallColormap(display, data->colormap);