input/pointer: try harder to not send duplicate motion events

wl_fixed_t is a 32-bit data type, but our doubles are 64-bit. This meant
that two doubles that would map to the same wl_fixed_t could compare
unequal, and send a duplicate motion event.

Refs swaywm/sway#4632.

types/seat/wlr_seat_pointer.c

@@ -230,18 +230,21 @@ void wlr_seat_pointer_send_motion(struct wlr_seat *wlr_seat, uint32_t time,
 		return;
 	}
 
-	if (wlr_seat->pointer_state.sx == sx && wlr_seat->pointer_state.sy == sy) {
-		return;
-	}
-
+	// Ensure we don't send duplicate motion events. Instead of comparing with an
+	// epsilon, chop off some precision by converting to a `wl_fixed_t` first,
+	// since that is what a client receives.
+	wl_fixed_t sx_fixed = wl_fixed_from_double(sx);
+	wl_fixed_t sy_fixed = wl_fixed_from_double(sy);
+	if (wl_fixed_from_double(wlr_seat->pointer_state.sx) != sx_fixed ||
+			wl_fixed_from_double(wlr_seat->pointer_state.sy) != sy_fixed) {
 		struct wl_resource *resource;
 		wl_resource_for_each(resource, &client->pointers) {
 			if (wlr_seat_client_from_pointer_resource(resource) == NULL) {
 				continue;
 			}
 
-		wl_pointer_send_motion(resource, time, wl_fixed_from_double(sx),
-			wl_fixed_from_double(sy));
+			wl_pointer_send_motion(resource, time, sx_fixed, sy_fixed);
+		}
 	}
 
 	wlr_seat_pointer_warp(wlr_seat, sx, sy);