static void DrawOperationBegin([NotNull] Player player, [NotNull] CommandReader cmd, [NotNull] DrawOperation op) {
IBrush brush = player.ConfigureBrush(cmd);
if (brush == null) return;
op.Brush = brush;
player.SelectionStart(op.ExpectedMarks, DrawOperationCallback, op, Permission.Draw);
player.Message("{0}: Click or &H/Mark&S {1} blocks.", op.Description, op.ExpectedMarks);
}