Pops up a dialog where you can select or specify an engine to be loaded.
You will always have to indicate whether you want to load the engine
as first or second engine, through the ‘Load menitioned engine as’
drop-down list at the bottom of the dialog.
You can even replace engines during a game, without disturbing that game.
(Beware that after loading an engine, XBoard will always be in Edit Game mode,
so you will have to tell the new engine what to do before it does anything!)
When you select an already installed engine from the ‘Select Engine from List’
drop-down list,
all other fields of the dialog will be ignored.
In other cases, you have to specify the engine executable,
possible arguments on the engine command line
(if the engine docs say the engine needs any),
and the directory where the engine should look for its files
(if this cannot be deduced automatically from the specification of the engine executable).
You will also have to specify (with the aid of checkboxes) if the engine is UCI.
If ‘Add this engine to the list’ is ticked (which it is by default),
the engine will be added to the list of installed engines in your settings file,
(provided you save the settings!),
so that next time you can select it from the drop-down list.
You can also specify a ‘nickname’,
under which the engine will then appear in that drop-down list,
and even choose to use that nickname for it in PGN files for engine-engine games.
The info you supply with the checkboxes whether the engine should use GUI book,
or (for variant engines) automatically switch to the current variant when loaded,
will also be included in the list.
For obsolete XBoard engines, which would normally take a long delay to load
because XBoard is waiting for a response they will not give,
you can tick ‘WB protocol v1’ to speed up the loading process.
Engine #N Settings
Pop up a menu dialog to alter the settings specific to the applicable engine.
(The second engine is only accessible once it has been used in Two-Machines mode.)
For each parameter the engine allows to be set,
a control element will appear in this dialog that can be used to alter the value.
Depending on the type of parameter (text string, number, multiple choice,
on/off switch, instantaneous signal) the appropriate control will appear,
with a description next to it.
XBoard has no idea what these values mean; it just passes them on to the engine.
How this dialog looks is completely determined by the engine,
and XBoard just passes it on to the user.
Many engines do not have any parameters that can be set by the user,
and in that case the dialog will be empty (except for the OK and cancel buttons).
UCI engines usually have many parameters. (But these are only visible with
a sufficiently modern version of the Polyglot adapter needed to run UCI engines,
e.g. Polyglot 1.4.55b.) For native XBoard engines this is less common.
Hint
Displays a move hint from the chess engine.
Book
Displays a list of possible moves from the chess engine's opening
book. The exact format depends on what chess engine you are using.
With GNU Chess 4, the first column gives moves, the second column
gives one possible response for each move, and the third column shows
the number of lines in the book that include the move from the first
column. If you select this option and nothing happens, the chess
engine is out of its book or does not support this feature.
Move Now
Forces the chess engine to move immediately. Chess engine mode only.
The Ctrl-M key is a keyboard equivalent.
Retract Move
Retracts your last move. In chess engine mode, you can do this only
after the chess engine has replied to your move; if the chess engine is still
thinking, use ‘Move Now’ first. In ICS mode, ‘Retract Move’
issues the command ‘takeback 1’ or ‘takeback 2’
depending on whether it is your opponent's move or yours.
The Ctrl-X key is a keyboard equivalent.
Recently Used Engines
At the bottom of the engine menu there can be a list of names
of engines that you recently loaded through the Load Engine menu dialog
in previous sessions.
Clicking on such a name will load that engine as first engine,
so you won't have to search for it in your list of installed engines,
if that is very long.
The maximum number of displayed engine names is set by the
recentEnginescommand-line option.