hints: Added SDL_HINT_QUIT_ON_LAST_WINDOW_CLOSE.

Fixes #2349.

include/SDL_hints.h

@@ -1943,6 +1943,30 @@ extern "C" {
  */
 #define SDL_HINT_X11_WINDOW_TYPE "SDL_X11_WINDOW_TYPE"
 
+/**
+ *  \brief  A variable that decides whether to send SDL_QUIT when closing the final window.
+ *
+ *  By default, SDL sends an SDL_QUIT event when there is only one window
+ *  and it receives an SDL_WINDOWEVENT_CLOSE event, under the assumption most
+ *  apps would also take the loss of this window as a signal to terminate the
+ *  program.
+ *
+ *  However, it's not unreasonable in some cases to have the program continue
+ *  to live on, perhaps to create new windows later.
+ *
+ *  Changing this hint to "0" will cause SDL to not send an SDL_QUIT event
+ *  when the final window is requesting to close. Note that in this case,
+ *  there are still other legitimate reasons one might get an SDL_QUIT
+ *  event: choosing "Quit" from the macOS menu bar, sending a SIGINT (ctrl-c)
+ *  on Unix, etc.
+ *
+ *  The default value is "1".  This hint can be changed at any time.
+ *
+ *  This hint is available since SDL 2.0.22. Before then, you always get
+ *  an SDL_QUIT event when closing the final window.
+ */
+#define SDL_HINT_QUIT_ON_LAST_WINDOW_CLOSE "SDL_QUIT_ON_LAST_WINDOW_CLOSE"
+
 
 /**
  *  \brief  An enumeration of hint priorities

src/events/SDL_windowevents.c

@@ -25,7 +25,7 @@
 #include "SDL_events.h"
 #include "SDL_events_c.h"
 #include "SDL_mouse_c.h"
-
+#include "SDL_hints.h"
 
 static int SDLCALL
 RemovePendingSizeChangedAndResizedEvents(void * userdata, SDL_Event *event)
@@ -201,8 +201,9 @@ SDL_SendWindowEvent(SDL_Window * window, Uint8 windowevent, int data1,
 
     if (windowevent == SDL_WINDOWEVENT_CLOSE) {
         if ( !window->prev && !window->next ) {
-            /* This is the last window in the list so send the SDL_QUIT event */
-            SDL_SendQuit();
+            if (SDL_GetHintBoolean(SDL_HINT_QUIT_ON_LAST_WINDOW_CLOSE, SDL_TRUE)) {
+                SDL_SendQuit();  /* This is the last window in the list so send the SDL_QUIT event */
+            }
         }
     }