view: assign output on surface creation instead of mapping...

...and notify the client of the preferred output scale when doing so.
This should allow clients to better determine an optimal size if they
are initially configured (unmapped) with zero size.

In particular, this fixes an issue with foot:

    https://codeberg.org/dnkl/foot/issues/1579

src/xdg.c

@@ -1,6 +1,8 @@
 // SPDX-License-Identifier: GPL-2.0-only
 
 #include <assert.h>
+#include <wlr/types/wlr_fractional_scale_v1.h>
+
 #include "common/macros.h"
 #include "common/mem.h"
 #include "decorations.h"
@@ -483,7 +485,13 @@ xdg_toplevel_view_map(struct view *view)
 	if (view->mapped) {
 		return;
 	}
+
 	view->mapped = true;
+
+	/*
+	 * An output should have been chosen when the surface was first
+	 * created, but take one more opportunity to assign an output if not.
+	 */
 	if (!view->output) {
 		view_set_output(view, output_nearest_to_cursor(view->server));
 	}
@@ -641,6 +649,17 @@ xdg_surface_new(struct wl_listener *listener, void *data)
 	view->impl = &xdg_toplevel_view_impl;
 	xdg_toplevel_view->xdg_surface = xdg_surface;
 
+	/*
+	 * Pick an output for the surface as soon as its created, so that the
+	 * client can be notified about any fractional scale before it is given
+	 * the chance to configure itself (and possibly pick its dimensions).
+	 */
+	view_set_output(view, output_nearest_to_cursor(server));
+	if (view->output) {
+		wlr_fractional_scale_v1_notify_scale(xdg_surface->surface,
+			view->output->wlr_output->scale);
+	}
+
 	view->workspace = server->workspace_current;
 	view->scene_tree = wlr_scene_tree_create(view->workspace->tree);
 	wlr_scene_node_set_enabled(&view->scene_tree->node, false);