transaction: Move centering to view_center_surface

This will allow us to reuse it for centering elsewhere.

include/sway/tree/view.h

@@ -317,6 +317,7 @@ void view_map(struct sway_view *view, struct wlr_surface *wlr_surface,
 void view_unmap(struct sway_view *view);
 
 void view_update_size(struct sway_view *view, int width, int height);
+void view_center_surface(struct sway_view *view);
 
 void view_child_init(struct sway_view_child *child,
 	const struct sway_view_child_impl *impl, struct sway_view *view,

sway/desktop/transaction.c

@@ -255,18 +255,7 @@ static void apply_container_state(struct sway_container *container,
 	// the container. This is important for fullscreen views which
 	// refuse to resize to the size of the output.
 	if (view && view->surface) {
-		if (view->geometry.width < container->current.content_width) {
-			container->surface_x = container->current.content_x +
-				(container->current.content_width - view->geometry.width) / 2;
-		} else {
-			container->surface_x = container->current.content_x;
-		}
-		if (view->geometry.height < container->current.content_height) {
-			container->surface_y = container->current.content_y +
-				(container->current.content_height - view->geometry.height) / 2;
-		} else {
-			container->surface_y = container->current.content_y;
-		}
+		view_center_surface(view);
 	}
 
 	if (!container->node.destroying) {

sway/tree/view.c

@@ -887,6 +887,16 @@ void view_update_size(struct sway_view *view, int width, int height) {
 	}
 }
 
+void view_center_surface(struct sway_view *view) {
+	struct sway_container *con = view->container;
+	// We always center the current coordinates rather than the next, as the
+	// geometry immediately affects the currently active rendering.
+	con->surface_x = fmax(con->current.content_x, con->current.content_x +
+			(con->current.content_width - view->geometry.width) / 2);
+	con->surface_y = fmax(con->current.content_y, con->current.content_y +
+			(con->current.content_height - view->geometry.height) / 2);
+}
+
 static const struct sway_view_child_impl subsurface_impl;
 
 static void subsurface_get_root_coords(struct sway_view_child *child,