cursor: send surface scale events

wlr_cursor is responsible for sending enter/leave events, but
doesn't send fractional-scale-v1 and wl_surface.preferred_buffer_scale
events. This is not an easy thing to do from a compositor, so let's
just do it in wlr_cursor itself.

types/wlr_cursor.c

@@ -6,6 +6,7 @@
 #include <stdlib.h>
 #include <wayland-server-core.h>
 #include <wlr/types/wlr_cursor.h>
+#include <wlr/types/wlr_fractional_scale_v1.h>
 #include <wlr/types/wlr_input_device.h>
 #include <wlr/types/wlr_output_layout.h>
 #include <wlr/types/wlr_output.h>
@@ -544,6 +545,16 @@ static void cursor_output_cursor_update(struct wlr_cursor_output_cursor *output_
 		} else {
 			wlr_surface_send_leave(surface, output);
 		}
+
+		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);
+		wlr_surface_set_preferred_buffer_scale(surface, ceil(scale));
 	} else if (cur->state->xcursor_name != NULL) {
 		struct wlr_xcursor_manager *manager = cur->state->xcursor_manager;
 		const char *name = cur->state->xcursor_name;