wayland/video: Validate the returned window display pointer before dereferencing it

If, in the case where all displays has been disconnected, and some window state change occurs before an active display is re-added and finalized, the pointer returned by SDL_GetDisplayForWindow() will be null necessitating that the returned pointer be checked for validity before dereferencing it.

src/video/SDL_video.c

@@ -1398,6 +1398,9 @@ static int SDL_UpdateFullscreenMode(SDL_Window *window, SDL_bool fullscreen)
 #endif
 
     display = SDL_GetDisplayForWindow(window);
+    if (display == NULL) { /* No display connected, nothing to do. */
+        return 0;
+    }
 
     if (fullscreen) {
         /* Hide any other fullscreen windows */

src/video/wayland/SDL_waylandwindow.c

@@ -59,12 +59,13 @@ SDL_FORCE_INLINE SDL_bool FloatEqual(float a, float b)
 static void GetFullScreenDimensions(SDL_Window *window, int *width, int *height, int *drawable_width, int *drawable_height)
 {
     SDL_WindowData *wind = (SDL_WindowData *)window->driverdata;
-    SDL_WaylandOutputData *output = (SDL_WaylandOutputData *)SDL_GetDisplayForWindow(window)->driverdata;
+    SDL_VideoDisplay *display = SDL_GetDisplayForWindow(window);
+    SDL_WaylandOutputData *output = display ? (SDL_WaylandOutputData *)display->driverdata : NULL;
 
     int fs_width, fs_height;
     int buf_width, buf_height;
-    const int output_width = wind->fs_output_width ? wind->fs_output_width : output->width;
-    const int output_height = wind->fs_output_height ? wind->fs_output_height : output->height;
+    const int output_width = wind->fs_output_width ? wind->fs_output_width : (output ? output->width : wind->window_width);
+    const int output_height = wind->fs_output_height ? wind->fs_output_height : (output ? output->height : wind->window_height);
 
     /*
      * Fullscreen desktop mandates a desktop sized window, so that's what applications will get.
@@ -133,7 +134,10 @@ static SDL_bool NeedViewport(SDL_Window *window)
 {
     SDL_WindowData *wind = window->driverdata;
     SDL_VideoData *video = wind->waylandData;
-    SDL_WaylandOutputData *output = ((SDL_WaylandOutputData *)SDL_GetDisplayForWindow(window)->driverdata);
+    SDL_VideoDisplay *display = SDL_GetDisplayForWindow(window);
+    SDL_WaylandOutputData *output = display ? ((SDL_WaylandOutputData *)display->driverdata) : NULL;
+    const int output_width = wind->fs_output_width ? wind->fs_output_width : (output ? output->width : wind->window_width);
+    const int output_height = wind->fs_output_height ? wind->fs_output_height : (output ? output->height : wind->window_height);
     int fs_width, fs_height;
 
     /*
@@ -144,7 +148,7 @@ static SDL_bool NeedViewport(SDL_Window *window)
     if (video->viewporter != NULL) {
         if (FullscreenModeEmulation(window)) {
             GetFullScreenDimensions(window, &fs_width, &fs_height, NULL, NULL);
-            if (fs_width != output->width || fs_height != output->height) {
+            if (fs_width != output_width || fs_height != output_height) {
                 return SDL_TRUE;
             }
         } else if (SurfaceScaleIsFractional(window) && (window->flags & SDL_WINDOW_ALLOW_HIGHDPI)) {
@@ -217,7 +221,8 @@ static void ConfigureWindowGeometry(SDL_Window *window)
 {
     SDL_WindowData *data = window->driverdata;
     SDL_VideoData *viddata = data->waylandData;
-    SDL_WaylandOutputData *output = (SDL_WaylandOutputData *)SDL_GetDisplayForWindow(window)->driverdata;
+    SDL_VideoDisplay *display = SDL_GetDisplayForWindow(window);
+    SDL_WaylandOutputData *output = display ? (SDL_WaylandOutputData *)display->driverdata : NULL;
     struct wl_region *region;
     const int old_dw = data->drawable_width;
     const int old_dh = data->drawable_height;
@@ -237,8 +242,8 @@ static void ConfigureWindowGeometry(SDL_Window *window)
 
     if (FullscreenModeEmulation(window) && NeedViewport(window)) {
         int fs_width, fs_height;
-        const int output_width = data->fs_output_width ? data->fs_output_width : output->width;
-        const int output_height = data->fs_output_height ? data->fs_output_height : output->height;
+        const int output_width = data->fs_output_width ? data->fs_output_width : (output ? output->width : data->window_width);
+        const int output_height = data->fs_output_height ? data->fs_output_height : (output ? output->height : data->window_height);
 
         window_size_changed = data->window_width != output_width || data->window_height != output_height;
 
@@ -559,7 +564,6 @@ static void handle_configure_xdg_toplevel(void *data,
 {
     SDL_WindowData *wind = (SDL_WindowData *)data;
     SDL_Window *window = wind->sdlwindow;
-    SDL_WaylandOutputData *driverdata;
 
     enum xdg_toplevel_state *state;
     SDL_bool fullscreen = SDL_FALSE;
@@ -586,8 +590,6 @@ static void handle_configure_xdg_toplevel(void *data,
         }
     }
 
-    driverdata = (SDL_WaylandOutputData *)SDL_GetDisplayForWindow(window)->driverdata;
-
     UpdateWindowFullscreen(window, fullscreen);
 
     if (!fullscreen) {
@@ -664,12 +666,6 @@ static void handle_configure_xdg_toplevel(void *data,
             window->h = height;
             wind->needs_resize_event = SDL_TRUE;
         }
-
-        /* This part is good though. */
-        if ((window->flags & SDL_WINDOW_ALLOW_HIGHDPI) && !FloatEqual(wind->scale_factor, driverdata->scale_factor)) {
-            wind->scale_factor = driverdata->scale_factor;
-            wind->needs_resize_event = SDL_TRUE;
-        }
     }
 }
 
@@ -819,12 +815,10 @@ static void decoration_frame_configure(struct libdecor_frame *frame,
 {
     SDL_WindowData *wind = (SDL_WindowData *)user_data;
     SDL_Window *window = wind->sdlwindow;
-    SDL_WaylandOutputData *driverdata;
     struct libdecor_state *state;
 
     enum libdecor_window_state window_state;
     int width, height;
-    float scale_factor = wind->scale_factor;
 
     SDL_bool focused = SDL_FALSE;
     SDL_bool fullscreen = SDL_FALSE;
@@ -844,8 +838,6 @@ static void decoration_frame_configure(struct libdecor_frame *frame,
     }
     floating = !(fullscreen || maximized || tiled);
 
-    driverdata = (SDL_WaylandOutputData *)SDL_GetDisplayForWindow(window)->driverdata;
-
     UpdateWindowFullscreen(window, fullscreen);
 
     if (!fullscreen) {
@@ -887,11 +879,6 @@ static void decoration_frame_configure(struct libdecor_frame *frame,
         if (FullscreenModeEmulation(window)) {
             GetFullScreenDimensions(window, &width, &height, NULL, NULL);
         }
-
-        /* This part is good though. */
-        if (window->flags & SDL_WINDOW_ALLOW_HIGHDPI) {
-            scale_factor = driverdata->scale_factor;
-        }
     } else if (!(window->flags & SDL_WINDOW_RESIZABLE) || (floating && wind->floating_resize_pending)) {
         width = window->windowed.w;
         height = window->windowed.h;
@@ -936,7 +923,7 @@ static void decoration_frame_configure(struct libdecor_frame *frame,
     wind->was_floating = floating;
 
     /* Do the resize on the SDL side (this will set window->w/h)... */
-    Wayland_HandleResize(window, width, height, scale_factor);
+    Wayland_HandleResize(window, width, height, wind->scale_factor);
 
     /* ... then commit the changes on the libdecor side. */
     state = libdecor_state_new(wind->window_width, wind->window_height);
@@ -1003,7 +990,7 @@ static const struct qt_extended_surface_listener extended_surface_listener = {
 
 static void update_scale_factor(SDL_WindowData *window)
 {
-    float old_factor = window->scale_factor;
+    const float old_factor = window->scale_factor;
     float new_factor;
     int i;
 
@@ -1012,14 +999,18 @@ static void update_scale_factor(SDL_WindowData *window)
         return;
     }
 
-    if (FULLSCREEN_VISIBLE(window->sdlwindow)) {
+    if (window->num_outputs == 0) {
+        /* No display connected, just fall back. */
+        new_factor = old_factor;
+    } else if (FULLSCREEN_VISIBLE(window->sdlwindow)) {
         /* For fullscreen, use the active display's scale factor */
         SDL_VideoDisplay *display = SDL_GetDisplayForWindow(window->sdlwindow);
-        SDL_WaylandOutputData *driverdata = display->driverdata;
-        new_factor = driverdata->scale_factor;
-    } else if (window->num_outputs == 0) {
-        /* No monitor (somehow)? Just fall back. */
-        new_factor = old_factor;
+        if (display) {
+            SDL_WaylandOutputData *driverdata = display->driverdata;
+            new_factor = driverdata->scale_factor;
+        } else {
+            new_factor = old_factor;
+        }
     } else {
         /* Check every display's factor, use the highest */
         new_factor = 0.0f;