surface: kill wlr_surface.previous

This wlr_surface_state field was a special case because we don't
want to save the whole current state: for instance, the wlr_buffer
must not be saved or else wouldn't get released soon enough.

Let's just inline the state fields we need instead.

include/wlr/types/wlr_surface.h

@@ -124,10 +124,9 @@ struct wlr_surface {
 	/**
 	 * `current` contains the current, committed surface state. `pending`
 	 * accumulates state changes from the client between commits and shouldn't
-	 * be accessed by the compositor directly. `previous` contains the state of
-	 * the previous commit.
+	 * be accessed by the compositor directly.
 	 */
-	struct wlr_surface_state current, pending, previous;
+	struct wlr_surface_state current, pending;
 
 	struct wl_list cached; // wlr_surface_state.cached_link
 
@@ -150,9 +149,18 @@ struct wlr_surface {
 
 	struct wl_list current_outputs; // wlr_surface_output::link
 
+	void *data;
+
+	// private state
+
 	struct wl_listener renderer_destroy;
 
-	void *data;
+	struct {
+		int32_t scale;
+		enum wl_output_transform transform;
+		int width, height;
+		int buffer_width, buffer_height;
+	} previous;
 };
 
 struct wlr_subsurface_state {

types/wlr_surface.c

@@ -444,7 +444,13 @@ static void surface_commit_state(struct wlr_surface *surface,
 	surface->sy += next->dy;
 	surface_update_damage(&surface->buffer_damage, &surface->current, next);
 
-	surface_state_copy(&surface->previous, &surface->current);
+	surface->previous.scale = surface->current.scale;
+	surface->previous.transform = surface->current.transform;
+	surface->previous.width = surface->current.width;
+	surface->previous.height = surface->current.height;
+	surface->previous.buffer_width = surface->current.buffer_width;
+	surface->previous.buffer_height = surface->current.buffer_height;
+
 	surface_state_move(&surface->current, next);
 
 	if (invalid_buffer) {
@@ -726,7 +732,6 @@ static void surface_handle_resource_destroy(struct wl_resource *resource) {
 	wl_list_remove(&surface->renderer_destroy.link);
 	surface_state_finish(&surface->pending);
 	surface_state_finish(&surface->current);
-	surface_state_finish(&surface->previous);
 	pixman_region32_fini(&surface->buffer_damage);
 	pixman_region32_fini(&surface->opaque_region);
 	pixman_region32_fini(&surface->input_region);
@@ -766,7 +771,6 @@ struct wlr_surface *surface_create(struct wl_client *client,
 
 	surface_state_init(&surface->current);
 	surface_state_init(&surface->pending);
-	surface_state_init(&surface->previous);
 	surface->pending.seq = 1;
 
 	wl_signal_init(&surface->events.commit);