Add support for fractional-scale-v1

References: https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/3511

sway/desktop/surface.c

@@ -2,6 +2,7 @@
 #include <stdlib.h>
 #include <time.h>
 #include <wlr/types/wlr_compositor.h>
+#include <wlr/types/wlr_fractional_scale_v1.h>
 #include "sway/server.h"
 #include "sway/surface.h"
 #include "sway/output.h"
@@ -46,12 +47,25 @@ void handle_compositor_new_surface(struct wl_listener *listener, void *data) {
 	}
 }
 
+static void surface_update_outputs(struct wlr_surface *surface) {
+	float scale = 1;
+	struct wlr_surface_output *surface_output;
+	wl_list_for_each(surface_output, &surface->current_outputs, link) {
+		if (surface_output->output->scale > scale) {
+			scale = surface_output->output->scale;
+		}
+	}
+	wlr_fractional_scale_v1_notify_scale(surface, scale);
+}
+
 void surface_enter_output(struct wlr_surface *surface,
 		struct sway_output *output) {
 	wlr_surface_send_enter(surface, output->wlr_output);
+	surface_update_outputs(surface);
 }
 
 void surface_leave_output(struct wlr_surface *surface,
 		struct sway_output *output) {
 	wlr_surface_send_leave(surface, output->wlr_output);
+	surface_update_outputs(surface);
 }

sway/server.c

@@ -14,6 +14,7 @@
 #include <wlr/types/wlr_data_control_v1.h>
 #include <wlr/types/wlr_drm.h>
 #include <wlr/types/wlr_export_dmabuf_v1.h>
+#include <wlr/types/wlr_fractional_scale_v1.h>
 #include <wlr/types/wlr_gamma_control_v1.h>
 #include <wlr/types/wlr_idle.h>
 #include <wlr/types/wlr_idle_notify_v1.h>
@@ -214,6 +215,7 @@ bool server_init(struct sway_server *server) {
 	wlr_single_pixel_buffer_manager_v1_create(server->wl_display);
 	server->content_type_manager_v1 =
 		wlr_content_type_manager_v1_create(server->wl_display, 1);
+	wlr_fractional_scale_manager_v1_create(server->wl_display, 1);
 
 	struct wlr_xdg_foreign_registry *foreign_registry =
 		wlr_xdg_foreign_registry_create(server->wl_display);