function result=EyelinkDoDriftCorrect(el, x, y, draw, allowsetup)

% USAGE: result=EyelinkDoDriftCorrect(el [, x, y, draw, allowsetup])
%
% el: eyelink default values
% x,y: position of driftcorrection target
% draw: set to 1 to draw driftcorrection target
% allowsetup: set to 1 to allow to go in to go to trackersetup
%
% Note that EyelinkDoDriftCorrect() internally uses Beeper() and Snd() to play
% auditory feedback tones if el.targetbeep=1 or el.feedbackbeep=1 and the
% el.callback function is set to the default PsychEyelinkDispatchCallback().
% If you want to use PsychPortAudio in a script that also calls EyelinkDoDriftCorrect,
% then read "help Snd" for instructions on how to provide proper interoperation
% between PsychPortAudio and the feedback sounds created by Eyelink.
%

% /********* PERFORM DRIFT CORRECTION ON TRACKER  *******/
%	/* Performs a drift correction, with target at (x,y). */
%	/* We are explicitly entering a tracker subfunction, */
%	/* so we have to handle link output explicitly. */
%	/* When we finish or abort the drift correction on the tracker, */
%	/* it won't go to another mode until we tell it to. */
%	/* For drift coorection, we can use the */
%	/* drift correction result message to tell when it's done, */
%	/* and what the result was. */

%	/*  Here we display the target ourselves (ignore target updates), */
%	/* wait for local spacebar or for operator trigger or */
%	/* ESC key abort. */
%	/* If operator aborts with ESC, we assume there's a setup */
%	/* problem and go to the setup menu. */

%	/* RETURNS: 0 if OK, 27 if Setup menu was called. */
%

% Eyelink Toolbox version
% 12-05-01	fwc created first version
% 12-05-01	fwc disabled unconditional erasing of screen
% 02-06-01	fwc removed use of global el, as suggested by John Palmer.
% 18-10-02	fwc	made sure missing variables were filled in with defaults
% 15-06-10  fwc added code for new callback version


result=-1; % initialize
if nargin < 1 || ~exist('el', 'var') || isempty(el)
	error( 'USAGE: result=EyelinkDoDriftCorrect(el [, x, y, draw, allowsetup])' );
end

% fill in missing variables
if ~exist('x', 'var') || ~exist('y', 'var') || isempty(x) || isempty(y)
	[x,y]=WindowCenter(el.window);
end

if ~exist('draw', 'var') || isempty(draw)
	draw=1;
end

if ~exist('allowsetup', 'var') || isempty(allowsetup)
	allowsetup=1;
end

% if we have the new callback code, we call it.
if ~isempty(el.callback)
    result = Eyelink('DriftCorrStart', x, y, 1, draw, allowsetup);
    return;
end

% else we continue with the old version

Eyelink('Command', 'heuristic_filter = ON');

targetrect=[0 0 0 0];

key=1;
while key~= 0
	[key, el]=EyelinkGetKey(el);		% dump old keys
end

if draw==1
	EyelinkClearCalDisplay(el);		% setup_cal_display()
	targetrect=EyelinkDrawCalTarget(el, x, y);     % we are told where it should be.
end

if el.targetbeep==1
	EyelinkCalTargetBeep(el);
end

status=Eyelink( 'DriftCorrStart', x, y);

tickcount=0;
result=el.NO_REPLY;
while result==el.NO_REPLY
	% check for result of drift correction
	result=Eyelink( 'CalResult' );
		
	[key, el]=EyelinkGetKey(el);		% getkey() HANDLE LOCAL KEY PRESS

	if el.mousetriggersdriftcorr==1 % allow mouse to trigger drift correction (fwc trick)
		[mx,my,button] = GetMouse(el.window);
		if button==1
			if IsInRect(mx,my,targetrect)
				key=el.SPACE_BAR; % fake a key press when mouse is pressed and on target
			end
		end	
	end

	switch key 
		case el.TERMINATE_KEY,       % breakout key code
			result=el.TERMINATE_KEY;
			return;
		case { 0,  el.JUNK_KEY	}	% No key
		case el.ESC_KEY,   % 27
			if el.allowlocalcontrol==1
				result=el.ESC_KEY;
			end
			if Eyelink('IsConnected') ==-1
				result=el.ESC_KEY;
			end
		case el.SPACE_BAR,	         		% 32: we trigger ourselves
			if el.allowlocaltrigger==1
				Eyelink( 'AcceptTrigger');
			end
			if Eyelink('IsConnected') == el.dummyconnected
				result=0;
			end
		otherwise,          % Echo to tracker for remote control
		    if el.allowlocalcontrol==1
	       		Eyelink('SendKeyButton', key, 0, el.KB_PRESS );
			end
	end % switch key
end % while cal_result==NO_REPLY

if draw==1
	EyelinkEraseCalTarget(el, targetrect); % bit superfluous actually
	EyelinkClearCalDisplay(el);	% exit_cal_display()
end

if result==el.ESC_KEY || result==-1	% Did we abort drift correction?
	% yes: go to setup menu to fix any problems
	if el.targetbeep==1
		EyelinkCalDoneBeep(el, 0);
	end
	if allowsetup==1
		EyelinkDoTrackerSetup(el);
	else
		Eyelink( 'SetOfflineMode');
	end
else
	% Otherwise, we apply the drift correction
	if el.targetbeep==1
		EyelinkCalDoneBeep(el, 1);
	end
	Eyelink('ApplyDriftCorr' );
	result=0;
end

return;