SDL: Added documentation for getting the X11 display from an SDL window

From ce4fe32ce37e8c38d966058b2e253675140c7bdb Mon Sep 17 00:00:00 2001
From: Sam Lantinga <[EMAIL REDACTED]>
Date: Thu, 28 Dec 2023 16:26:55 -0800
Subject: [PATCH] Added documentation for getting the X11 display from an SDL
 window

---
 docs/README-migration.md | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/docs/README-migration.md b/docs/README-migration.md
index ccf3734b86ce..c2a58f185faa 100644
--- a/docs/README-migration.md
+++ b/docs/README-migration.md
@@ -1219,11 +1219,13 @@ The information previously available in SDL_GetWindowWMInfo() is now available a
         ...
     }
 #elif defined(__LINUX__)
+    Display *xdisplay = NULL;
     Window xwindow = 0;
     if (SDL_GetWindowWMInfo(window, &info) && info.subsystem == SDL_SYSWM_X11) {
+        xdisplay = info.info.x11.display;
         xwindow = info.info.x11.window;
     }
-    if (xwindow) {
+    if (xdisplay && xwindow) {
         ...
     }
 #endif
@@ -1241,8 +1243,9 @@ becomes:
         ...
     }
 #elif defined(__LINUX__)
+    Display *xdisplay = (Display *)SDL_GetProperty(SDL_GetWindowProperties(window), "SDL.window.x11.display", NULL);
     Window xwindow = (Window)SDL_GetNumberProperty(SDL_GetWindowProperties(window), "SDL.window.x11.window", 0);
-    if (xwindow) {
+    if (xdisplay && xwindow) {
         ...
     }
 #endif