wayland: Always use the requested compositor dimensions for fullscreen windows

In the event that the compositor sends window dimensions of (0,0), use the last requested compositor dimensions for fullscreen windows as opposed to trying to guess the target dimensions from the output, which can be null if no outputs are present, or wrong in the case of multi-display setups.  Fullscreen windows must respect the maximum dimensions reported by the compositor, or a protocol violation can result.

This also prevents possible crashes if the compositor sends a config event with dimensions of (0,0) before a display has been added and/or finalized.

src/video/wayland/SDL_waylandwindow.c

@@ -109,20 +109,17 @@ static SDL_bool WindowNeedsViewport(SDL_Window *window)
 {
     SDL_WindowData *wind = window->driverdata;
     SDL_VideoData *video = wind->waylandData;
-    SDL_DisplayData *output = SDL_GetDisplayDriverDataForWindow(window);
-    const int output_width = wind->requested_window_width ? wind->requested_window_width : output->screen_width;
-    const int output_height = wind->requested_window_height ? wind->requested_window_height : output->screen_height;
 
     /*
      * A viewport is only required when scaling is enabled and:
      *  - The surface scale is fractional.
-     *  - A fullscreen mode is being emulated and the mode does not match the logical desktop dimensions.
+     *  - An exclusive fullscreen mode is being emulated and the mode does not match the requested output size.
      */
     if (video->viewporter != NULL) {
         if (SurfaceScaleIsFractional(window)) {
             return SDL_TRUE;
         } else if (window->fullscreen_exclusive) {
-            if (window->current_fullscreen_mode.w != output_width || window->current_fullscreen_mode.h != output_height) {
+            if (window->current_fullscreen_mode.w != wind->requested_window_width || window->current_fullscreen_mode.h != wind->requested_window_height) {
                 return SDL_TRUE;
             }
         }
@@ -238,7 +235,6 @@ static void ConfigureWindowGeometry(SDL_Window *window)
 {
     SDL_WindowData *data = window->driverdata;
     SDL_VideoData *viddata = data->waylandData;
-    SDL_DisplayData *output = SDL_GetDisplayDriverDataForWindow(window);
     const int old_dw = data->drawable_width;
     const int old_dh = data->drawable_height;
     int window_width, window_height;
@@ -257,9 +253,8 @@ static void ConfigureWindowGeometry(SDL_Window *window)
     }
 
     if (data->is_fullscreen && window->fullscreen_exclusive) {
-        /* If the compositor supplied fullscreen dimensions, use them, otherwise fall back to the display dimensions. */
-        int output_width = data->requested_window_width ? data->requested_window_width : output->screen_width;
-        int output_height = data->requested_window_height ? data->requested_window_height : output->screen_height;
+        int output_width = data->requested_window_width;
+        int output_height = data->requested_window_height;
         window_width = window->current_fullscreen_mode.w;
         window_height = window->current_fullscreen_mode.h;
 
@@ -737,6 +732,11 @@ static void handle_configure_xdg_toplevel(void *data,
                 xdg_toplevel_set_fullscreen(xdg_toplevel, disp->driverdata->output);
             }
         }
+
+        if (width == 0 || height == 0) {
+            width = wind->requested_window_width;
+            height = wind->requested_window_height;
+        }
     }
 
     /* Similar to maximized/restore events above, send focus events too! */
@@ -982,8 +982,8 @@ static void decoration_frame_configure(struct libdecor_frame *frame,
          * told to do this.
          */
         if (!libdecor_configuration_get_content_size(configuration, frame, &width, &height)) {
-            width = 0;
-            height = 0;
+            width = wind->requested_window_width;
+            height = wind->requested_window_height;
         }
     } else {
         if (!(window->flags & SDL_WINDOW_RESIZABLE)) {