desktop-shell: Properly handle lowered fullscreen surfaces

lower_fullscreen_surface() was removing fullscreen surfaces from
the fullscreen layer and inserting them in the normal workspace
layer. However, those fullscreen surfaces were never put back in
the fullscreen layer, causing bugs such as unrelated surfaces
being drawn between a fullscreen surface and its black view.

Change the lower_fullscreen_surface() logic so that it lowers
fullscreen surfaces to the workspace layer *and* hides the
black views. Make this reversible by re-configuring the lowered
fullscreen surface: when it is re-configured, the black view
will be shown again and the surface will be restacked in the
fullscreen layer.

https://bugs.freedesktop.org/show_bug.cgi?id=73575
https://bugs.freedesktop.org/show_bug.cgi?id=74221
https://bugs.freedesktop.org/show_bug.cgi?id=74222

desktop-shell/exposay.c

@@ -160,7 +160,7 @@ exposay_highlight_surface(struct desktop_shell *shell,
 	shell->exposay.column_current = esurface->column;
 	shell->exposay.cur_output = esurface->eoutput;
 
-	activate(shell, view->surface, shell->exposay.seat);
+	activate(shell, view->surface, shell->exposay.seat, false);
 	shell->exposay.focus_current = view;
 }
 
@@ -318,8 +318,6 @@ exposay_layout(struct desktop_shell *shell, struct shell_output *shell_output)
 		if (shell->exposay.focus_current == esurface->view)
 			highlight = esurface;
 
-		set_alpha_if_fullscreen(get_shell_surface(view->surface));
-
 		exposay_animate_in(esurface);
 
 		i++;
@@ -538,10 +536,10 @@ exposay_transition_inactive(struct desktop_shell *shell, int switch_focus)
 	 * to the new. */
 	if (switch_focus && shell->exposay.focus_current)
 		activate(shell, shell->exposay.focus_current->surface,
-		         shell->exposay.seat);
+		         shell->exposay.seat, true);
 	else if (shell->exposay.focus_prev)
 		activate(shell, shell->exposay.focus_prev->surface,
-		         shell->exposay.seat);
+		         shell->exposay.seat, true);
 
 	wl_list_for_each(esurface, &shell->exposay.surface_list, link)
 		exposay_animate_out(esurface);

desktop-shell/shell.c

@@ -166,6 +166,7 @@ struct shell_surface {
 		bool maximized;
 		bool fullscreen;
 		bool relative;
+		bool lowered;
 	} state, next_state, requested_state; /* surface states */
 	bool state_changed;
 	bool state_requested;
@@ -234,13 +235,6 @@ struct shell_client {
 	int unresponsive;
 };
 
-void
-set_alpha_if_fullscreen(struct shell_surface *shsurf)
-{
-	if (shsurf && shsurf->state.fullscreen)
-		shsurf->fullscreen.black_view->alpha = 0.25;
-}
-
 static struct desktop_shell *
 shell_surface_get_shell(struct shell_surface *shsurf);
 
@@ -630,7 +624,7 @@ focus_state_surface_destroy(struct wl_listener *listener, void *data)
 	shell = state->seat->compositor->shell_interface.shell;
 	if (next) {
 		state->keyboard_focus = NULL;
-		activate(shell, next, state->seat);
+		activate(shell, next, state->seat, true);
 	} else {
 		if (shell->focus_animation_type == ANIMATION_DIM_LAYER) {
 			if (state->ws->focus_animation)
@@ -1839,10 +1833,10 @@ busy_cursor_grab_button(struct weston_pointer_grab *base,
 	struct weston_seat *seat = grab->grab.pointer->seat;
 
 	if (shsurf && button == BTN_LEFT && state) {
-		activate(shsurf->shell, shsurf->surface, seat);
+		activate(shsurf->shell, shsurf->surface, seat, true);
 		surface_move(shsurf, seat, 0);
 	} else if (shsurf && button == BTN_RIGHT && state) {
-		activate(shsurf->shell, shsurf->surface, seat);
+		activate(shsurf->shell, shsurf->surface, seat, true);
 		surface_rotate(shsurf, seat);
 	}
 }
@@ -2157,7 +2151,7 @@ shell_surface_calculate_layer_link (struct shell_surface *shsurf)
 	switch (shsurf->type) {
 	case SHELL_SURFACE_POPUP:
 	case SHELL_SURFACE_TOPLEVEL:
-		if (shsurf->state.fullscreen) {
+		if (shsurf->state.fullscreen && !shsurf->state.lowered) {
 			return &shsurf->shell->fullscreen_layer.view_list;
 		} else if (shsurf->parent) {
 			/* Move the surface to its parent layer so
@@ -2540,7 +2534,7 @@ set_minimized(struct weston_surface *surface, uint32_t is_true)
 		wl_list_for_each(seat, &shsurf->shell->compositor->seat_list, link) {
 			if (!seat->keyboard)
 				continue;
-			activate(shsurf->shell, view->surface, seat);
+			activate(shsurf->shell, view->surface, seat, true);
 		}
 	}
 
@@ -2703,6 +2697,8 @@ shell_ensure_fullscreen_black_view(struct shell_surface *shsurf)
 	               &shsurf->fullscreen.black_view->layer_link);
 	weston_view_geometry_dirty(shsurf->fullscreen.black_view);
 	weston_surface_damage(shsurf->surface);
+
+	shsurf->state.lowered = false;
 }
 
 /* Create black surface and append it to the associated fullscreen surface.
@@ -2719,6 +2715,10 @@ shell_configure_fullscreen(struct shell_surface *shsurf)
 	if (shsurf->fullscreen.type != WL_SHELL_SURFACE_FULLSCREEN_METHOD_DRIVER)
 		restore_output_mode(output);
 
+	/* Reverse the effect of lower_fullscreen_layer() */
+	wl_list_remove(&shsurf->view->layer_link);
+	wl_list_insert(&shsurf->shell->fullscreen_layer.view_list, &shsurf->view->layer_link);
+
 	shell_ensure_fullscreen_black_view(shsurf);
 
 	surface_subsurfaces_boundingbox(shsurf->surface, &surf_x, &surf_y,
@@ -4436,8 +4436,12 @@ rotate_binding(struct weston_seat *seat, uint32_t time, uint32_t button,
 	surface_rotate(surface, seat);
 }
 
-/* Move all fullscreen layers down to the current workspace in a non-reversible
- * manner. This should be used when implementing shell-wide overlays, such as
+/* Move all fullscreen layers down to the current workspace and hide their
+ * black views. The surfaces' state is set to both fullscreen and lowered,
+ * and this is reversed when such a surface is re-configured, see
+ * shell_configure_fullscreen() and shell_ensure_fullscreen_black_view().
+ *
+ * This should be used when implementing shell-wide overlays, such as
  * the alt-tab switcher, which need to de-promote fullscreen layers. */
 void
 lower_fullscreen_layer(struct desktop_shell *shell)
@@ -4449,16 +4453,32 @@ lower_fullscreen_layer(struct desktop_shell *shell)
 	wl_list_for_each_reverse_safe(view, prev,
 				      &shell->fullscreen_layer.view_list,
 				      layer_link) {
+		struct shell_surface *shsurf = get_shell_surface(view->surface);
+
+		if (!shsurf)
+			continue;
+
+		/* We can have a non-fullscreen popup for a fullscreen surface
+		 * in the fullscreen layer. */
+		if (shsurf->state.fullscreen) {
+			/* Hide the black view */
+			wl_list_remove(&shsurf->fullscreen.black_view->layer_link);
+			wl_list_init(&shsurf->fullscreen.black_view->layer_link);
+		}
+
+		/* Lower the view to the workspace layer */
 		wl_list_remove(&view->layer_link);
 		wl_list_insert(&ws->layer.view_list, &view->layer_link);
 		weston_view_damage_below(view);
 		weston_surface_damage(view->surface);
+
+		shsurf->state.lowered = true;
 	}
 }
 
 void
 activate(struct desktop_shell *shell, struct weston_surface *es,
-	 struct weston_seat *seat)
+	 struct weston_seat *seat, bool configure)
 {
 	struct weston_surface *main_surface;
 	struct focus_state *state;
@@ -4482,7 +4502,7 @@ activate(struct desktop_shell *shell, struct weston_surface *es,
 	shsurf = get_shell_surface(main_surface);
 	assert(shsurf);
 
-	if (shsurf->state.fullscreen)
+	if (shsurf->state.fullscreen && configure)
 		shell_configure_fullscreen(shsurf);
 	else
 		restore_all_output_modes(shell->compositor);
@@ -4531,7 +4551,7 @@ activate_binding(struct weston_seat *seat,
 	if (get_shell_surface_type(main_surface) == SHELL_SURFACE_NONE)
 		return;
 
-	activate(shell, focus, seat);
+	activate(shell, focus, seat, true);
 }
 
 static void
@@ -4951,7 +4971,7 @@ map(struct desktop_shell *shell, struct shell_surface *shsurf,
 		if (shell->locked)
 			break;
 		wl_list_for_each(seat, &compositor->seat_list, link)
-			activate(shell, shsurf->surface, seat);
+			activate(shell, shsurf->surface, seat, true);
 		break;
 	case SHELL_SURFACE_POPUP:
 	case SHELL_SURFACE_NONE:
@@ -5402,7 +5422,7 @@ switcher_destroy(struct switcher *switcher)
 
 	if (switcher->current)
 		activate(switcher->shell, switcher->current,
-			 (struct weston_seat *) keyboard->seat);
+			 (struct weston_seat *) keyboard->seat, true);
 	wl_list_remove(&switcher->listener.link);
 	weston_keyboard_end_grab(keyboard);
 	if (keyboard->input_method_resource)

desktop-shell/shell.h

@@ -206,9 +206,6 @@ struct desktop_shell {
 	char *client;
 };
 
-void
-set_alpha_if_fullscreen(struct shell_surface *shsurf);
-
 struct weston_output *
 get_default_output(struct weston_compositor *compositor);
 
@@ -226,7 +223,7 @@ lower_fullscreen_layer(struct desktop_shell *shell);
 
 void
 activate(struct desktop_shell *shell, struct weston_surface *es,
-	 struct weston_seat *seat);
+	 struct weston_seat *seat, bool configure);
 
 void
 exposay_binding(struct weston_seat *seat,