cursor: ensure theme loaded on output creation

river/Cursor.zig

@@ -118,7 +118,8 @@ pub fn deinit(self: *Self) void {
 }
 
 /// Set the cursor theme for the given seat, as well as the xwayland theme if
-/// this is the default seat.
+/// this is the default seat. Either argument may be null, in which case a
+/// default will be used.
 pub fn setTheme(self: *Self, theme: ?[*:0]const u8, _size: ?u32) !void {
     const server = self.seat.input_manager.server;
     const size = _size orelse default_size;

river/Output.zig

@@ -142,6 +142,15 @@ pub fn init(self: *Self, root: *Root, wlr_output: *c.wlr_output) !void {
         // layout. This automatically creates an output global on the wl_display.
         c.wlr_output_layout_add_auto(root.wlr_output_layout, wlr_output);
 
+        // Ensure that a cursor image at the output's scale factor is loaded
+        // for each seat.
+        var it = root.server.input_manager.seats.first;
+        while (it) |node| : (it = node.next) {
+            const seat = &node.data;
+            if (!c.wlr_xcursor_manager_load(seat.cursor.wlr_xcursor_manager, wlr_output.scale))
+                log.err(.cursor, "failed to load xcursor theme at scale {}", .{wlr_output.scale});
+        }
+
         var width: c_int = undefined;
         var height: c_int = undefined;
         c.wlr_output_effective_resolution(wlr_output, &width, &height);