video: Use the explicit fullscreen display for a window unless the window was moved

 When an exclusive fullscreen display is specified, it overrides any positioning, including from driver specific functions. Allows for the proper placement of fullscreen windows on macOS and Windows when the floating window is on a display that differs from the one specified by the exclusive fullscreen mode.

 A specific position-only function has been split out for use when a window has been moved.

src/video/SDL_video.c

@@ -1226,11 +1226,12 @@ SDL_DisplayID SDL_GetDisplayForWindowCoordinate(int coordinate)
     return displayID;
 }
 
-SDL_DisplayID SDL_GetDisplayForWindow(SDL_Window *window)
+static SDL_DisplayID SDL_GetDisplayForWindowPosition(SDL_Window *window)
 {
     SDL_DisplayID displayID = 0;
 
     CHECK_WINDOW_MAGIC(window, 0);
+
     if (_this->GetDisplayForWindow) {
         displayID = _this->GetDisplayForWindow(_this, window);
     }
@@ -1248,10 +1249,41 @@ SDL_DisplayID SDL_GetDisplayForWindow(SDL_Window *window)
     if (!displayID) {
         displayID = GetDisplayForRect(window->x, window->y, window->w, window->h);
     }
-    if (!displayID && (window->flags & SDL_WINDOW_FULLSCREEN)) {
-        /* Use the explicit fullscreen display if retrieval via the window position fails */
+    if (!displayID) {
+        /* Use the primary display for a window if we can't find it anywhere else */
+        displayID = SDL_GetPrimaryDisplay();
+    }
+    return displayID;
+}
+
+SDL_DisplayID SDL_GetDisplayForWindow(SDL_Window *window)
+{
+    SDL_DisplayID displayID = 0;
+
+    CHECK_WINDOW_MAGIC(window, 0);
+
+    /* An explicit fullscreen display overrides all */
+    if (window->flags & SDL_WINDOW_FULLSCREEN) {
         displayID = window->fullscreen_mode.displayID;
     }
+
+    if (!displayID && _this->GetDisplayForWindow) {
+        displayID = _this->GetDisplayForWindow(_this, window);
+    }
+
+    /* A backend implementation may fail to get a display for the window
+     * (for example if the window is off-screen), but other code may expect it
+     * to succeed in that situation, so we fall back to a generic position-
+     * based implementation in that case. */
+    if (!displayID) {
+        displayID = SDL_GetDisplayForWindowCoordinate(window->windowed.x);
+    }
+    if (!displayID) {
+        displayID = SDL_GetDisplayForWindowCoordinate(window->windowed.y);
+    }
+    if (!displayID) {
+        displayID = GetDisplayForRect(window->x, window->y, window->w, window->h);
+    }
     if (!displayID) {
         /* Use the primary display for a window if we can't find it anywhere else */
         displayID = SDL_GetPrimaryDisplay();
@@ -1261,7 +1293,7 @@ SDL_DisplayID SDL_GetDisplayForWindow(SDL_Window *window)
 
 void SDL_CheckWindowDisplayChanged(SDL_Window *window)
 {
-    SDL_DisplayID displayID = SDL_GetDisplayForWindow(window);
+    SDL_DisplayID displayID = SDL_GetDisplayForWindowPosition(window);
 
     if (displayID != window->last_displayID) {
         int i, display_index;
@@ -1498,17 +1530,8 @@ int SDL_SetWindowFullscreenMode(SDL_Window *window, const SDL_DisplayMode *mode)
 
     if (SDL_WINDOW_FULLSCREEN_VISIBLE(window)) {
         SDL_UpdateFullscreenMode(window, SDL_TRUE);
-    } else if (window->flags & SDL_WINDOW_FULLSCREEN) {
-        /* If fullscreen and not visible, just update the position so the window will be
-         * on the correct display when shown/restored.
-         */
-        if (mode) {
-            SDL_Rect r;
-            if (SDL_GetDisplayBounds(mode->displayID, &r) == 0) {
-                SDL_SendWindowEvent(window, SDL_EVENT_WINDOW_MOVED, r.x, r.y);
-            }
-        }
     }
+
     return 0;
 }