win32: Keep the window on the last maximized display when leaving fullscreen

A window may have been maximized by dragging it to the top of another display, in which case the floating position may be out-of-date. If the window is being restored to maximized, and the maximized and floating position are on different displays, try to center the window on the maximized display for restoration, which mimics native Windows behavior.

Author: Kontrabant

src/video/windows/SDL_windowswindow.c

@@ -1391,6 +1391,35 @@ SDL_FullscreenResult WIN_SetWindowFullscreen(SDL_VideoDevice *_this, SDL_Window
                                       &w, &h,
                                       SDL_WINDOWRECT_FLOATING);
         data->windowed_mode_was_maximized = false;
+
+        /* A window may have been maximized by dragging it to the top of another display, in which case the floating
+         * position may be out-of-date. If the window is being restored to maximized, and the maximized and floating
+         * position are on different displays, try to center the window on the maximized display for restoration, which
+         * mimics native Windows behavior.
+         */
+        if (enterMaximized) {
+            const SDL_Point windowed_point = { window->windowed.x, window->windowed.y };
+            const SDL_Point floating_point = { window->floating.x, window->floating.y };
+            const SDL_DisplayID floating_display = SDL_GetDisplayForPoint(&floating_point);
+            const SDL_DisplayID windowed_display = SDL_GetDisplayForPoint(&windowed_point);
+
+            if (floating_display != windowed_display) {
+                SDL_Rect bounds;
+
+                SDL_zero(bounds);
+                SDL_GetDisplayUsableBounds(windowed_display, &bounds);
+                if (w < bounds.w) {
+                    x = bounds.x + (bounds.w - w) / 2;
+                } else {
+                    x = bounds.x;
+                }
+                if (h < bounds.h) {
+                    y = bounds.y + (bounds.h - h) / 2;
+                } else {
+                    y = bounds.y;
+                }
+            }
+        }
     }
 
     /* Always reset the window to the base floating size before possibly re-applying the maximized state,