wayland: handle all outputs disappearing without segfaulting

If you switch TTYs while mpv is playing, wlroots compositors will remove
all outputs from the registry. This segfaults when you switch back since
we try to access cleared memory. Rework this so wl->current_output is
given null when appropriate and properly guarded. You still need at
least one output to initially place the surface, but in general they can
all disappear during runtime and it should work. Change the log to
verbose because that becomes just noise in this case (switching TTYs).
The surface entrance event happens later and should get all the proper
parameters.

Author: Dudemanguy

video/out/wayland_common.c

@@ -328,8 +328,7 @@ static void rescale_geometry(struct vo_wayland_state *wl, double old_scale);
 static void set_geometry(struct vo_wayland_state *wl, bool resize);
 static void set_surface_scaling(struct vo_wayland_state *wl);
 static void update_output_scaling(struct vo_wayland_state *wl);
-static void update_output_geometry(struct vo_wayland_state *wl, struct mp_rect old_geometry,
-                                   struct mp_rect old_output_geometry);
+static void update_output_geometry(struct vo_wayland_state *wl);
 static void destroy_offer(struct vo_wayland_data_offer *o);
 
 /* Wayland listener boilerplate */
@@ -1670,13 +1669,13 @@ static void surface_handle_enter(void *data, struct wl_surface *wl_surface,
                                  struct wl_output *output)
 {
     struct vo_wayland_state *wl = data;
-    if (!wl->current_output)
-        return;
 
-    struct mp_rect old_output_geometry = wl->current_output->geometry;
-    struct mp_rect old_geometry = wl->geometry;
-    wl->current_output = NULL;
+    if (wl->current_output) {
+        wl->old_output_geometry = wl->current_output->geometry;
+        wl->old_geometry = wl->geometry;
+    }
 
+    wl->current_output = NULL;
     int outputs = 0;
     struct vo_wayland_output *o;
     wl_list_for_each(o, &wl->output_list, link) {
@@ -1689,7 +1688,7 @@ static void surface_handle_enter(void *data, struct wl_surface *wl_surface,
     }
 
     if (outputs == 1)
-        update_output_geometry(wl, old_geometry, old_output_geometry);
+        update_output_geometry(wl);
 
     MP_VERBOSE(wl, "Surface entered output %s %s (%s) (0x%x), scale = %f, refresh rate = %f Hz\n",
                wl->current_output->make, wl->current_output->model, wl->current_output->name,
@@ -1702,11 +1701,11 @@ static void surface_handle_leave(void *data, struct wl_surface *wl_surface,
                                  struct wl_output *output)
 {
     struct vo_wayland_state *wl = data;
-    if (!wl->current_output)
-        return;
 
-    struct mp_rect old_output_geometry = wl->current_output->geometry;
-    struct mp_rect old_geometry = wl->geometry;
+    if (wl->current_output) {
+        wl->old_output_geometry = wl->current_output->geometry;
+        wl->old_geometry = wl->geometry;
+    }
 
     int outputs = 0;
     struct vo_wayland_output *o;
@@ -1719,8 +1718,11 @@ static void surface_handle_leave(void *data, struct wl_surface *wl_surface,
             wl->current_output = o;
     }
 
+    if (!outputs)
+        wl->current_output = NULL;
+
     if (outputs == 1)
-        update_output_geometry(wl, old_geometry, old_output_geometry);
+        update_output_geometry(wl);
 
     wl->pending_vo_events |= VO_EVENT_WIN_STATE;
 }
@@ -2828,6 +2830,8 @@ static void registry_handle_remove(void *data, struct wl_registry *reg, uint32_t
     wl_list_for_each_safe(output, output_tmp, &wl->output_list, link) {
         if (output->id == id) {
             remove_output(output);
+            if (wl_list_length(&wl->output_list) == 0)
+                wl->current_output = NULL;
             return;
         }
     }
@@ -3183,7 +3187,7 @@ static struct vo_wayland_output *find_output(struct vo_wayland_state *wl)
             return output;
     }
     if (!fallback_output) {
-        MP_ERR(wl, "No screens could be found!\n");
+        MP_VERBOSE(wl, "No screens could be found!\n");
         return NULL;
     } else if (screen_id >= 0) {
         MP_WARN(wl, "Screen index %i not found/unavailable! Falling back to screen 0!\n", screen_id);
@@ -3885,8 +3889,7 @@ static void update_output_scaling(struct vo_wayland_state *wl)
     wl->pending_vo_events |= VO_EVENT_DPI | VO_EVENT_RESIZE;
 }
 
-static void update_output_geometry(struct vo_wayland_state *wl, struct mp_rect old_geometry,
-                                   struct mp_rect old_output_geometry)
+static void update_output_geometry(struct vo_wayland_state *wl)
 {
     if (wl->need_rescale) {
         update_output_scaling(wl);
@@ -3895,20 +3898,20 @@ static void update_output_geometry(struct vo_wayland_state *wl, struct mp_rect o
 
     bool force_resize = false;
     bool use_output_scale = wl_surface_get_version(wl->surface) < 6 &&
-                            !wl->fractional_scale_manager &&
+                            !wl->fractional_scale_manager && wl->current_output &&
                             wl->scaling != wl->current_output->scale;
 
     if (use_output_scale) {
         set_surface_scaling(wl);
         force_resize = true;
     }
 
-    if (!mp_rect_equals(&old_output_geometry, &wl->current_output->geometry)) {
+    if (!mp_rect_equals(&wl->old_output_geometry, &wl->current_output->geometry)) {
         set_geometry(wl, false);
         force_resize = true;
     }
 
-    if (!mp_rect_equals(&old_geometry, &wl->geometry) || force_resize)
+    if (!mp_rect_equals(&wl->old_geometry, &wl->geometry) || force_resize)
         wl->pending_vo_events |= VO_EVENT_RESIZE;
 }
 
@@ -4704,7 +4707,7 @@ void vo_wayland_wait_frame(struct vo_wayland_state *wl)
     if (vblank_time <= 0 && wl->refresh_interval > 0)
         vblank_time = wl->refresh_interval;
 
-    if (vblank_time <= 0 && wl->current_output->refresh_rate > 0)
+    if (vblank_time <= 0 && wl->current_output && wl->current_output->refresh_rate > 0)
         vblank_time = 1e9 / wl->current_output->refresh_rate;
 
     // Ideally you should never reach this point.

video/out/wayland_common.h

@@ -58,6 +58,8 @@ struct vo_wayland_state {
     struct mp_rect window_size;
     struct wl_list output_list;
     struct vo_wayland_output *current_output;
+    struct mp_rect old_geometry;
+    struct mp_rect old_output_geometry;
     int bounded_height;
     int bounded_width;
     int reduced_height;