function [eye,a]=EyeTracking(cmd,eye)

% [eye,a]=EyeTracking(cmd,eye)
% initiates eye tracking params, tracks, and tests for eye-in-window
% if eye.trackEYES=1, otherwise does nothing
% 
% INPUTS: 
%		cmd: determines action
%		eye: a structure of eye-trecking params and data
% OUTPUTS:
%		a: a matrix with the last eye position results
%
% USAGE:
%		cmd='init' initiates parameters. Make appropriate changes to desired params after
%		this call
%		cmd='trackEye' - place this call in the loop that displays each stimulus frame
%		cmd='resetArray' - place this call before each stimulus presentation trial
%		cmd='getEyePosArray' - place this call after each stim presentation trial with
%				output parameter a (and save eye position data in it, if needed.
%		cmd='setZero' - sets zero value (the center for the eye window)
%		cmd='isINwindow' - tests whether eye is whithin a circular window; needs 
%				a second output parameter a: a=1, if eye is whithin predefined radius
%				from the center (zero point), and a=0, if it is not

% gtb 01/20/2001

global display;

a=[];
if ~eye.trackEYES, return; end;

switch cmd,
case 'init',
	eye.winrad=1024;  % eye window in pixels
	eye.plotEYEpos=0; % change this value after initiation if want plotting
	numPts=3600;
	eye.Array=zeros(numPts,2); % use smaller array if things slow down
	eye.Samples=0;
	% change these below!
	eye.pos=[0 0];
	eye.rad=3; % radius of the eye position spot
	eye.maxin=10;
	if exist('eyePositions.mat')  %this file is generated by eyecalib
		load eyePositions;
		eye.zero=mean(eyePositions'); 
	else
		eye.zero=[];
	end;

case 'resetArray',
    eye.Samples=0; eye.Array=zeros(numPts,2);

case 'setZero',
 	datain=mean(analin2ch(4,20)); % ie /10*2048.
	eye.pos(1)=round(datain(1)*display.X/2/eye.maxin+display.X/2);
	eye.pos(2)=round(display.Y-datain(2)*display.Y/2/eye.maxin-display.Y/2);
	eye.zero=eye.pos;

case 'isINwindow',
	if nargout<2, error('Need 2 output params with this command'); end;
 	datain=mean(analin2ch(4,20)); % ie /10*2048.
	eye.pos(1)=round(datain(1)*display.X/2/eye.maxin+display.X/2);
	eye.pos(2)=round(display.Y-datain(2)*display.Y/2/eye.maxin-display.Y/2);
	if sum((eye.pos-eye.zero).^2) > eye.winrad^2, a=0; 
	else a=1; end;

case 'trackEye',
	eye.Samples=eye.Samples+1;
	if isfield(eye,'plotEYEpos'), if eye.plotEYEpos,
		%erasing old eye position
 		SCREEN(display.windowPtr,'FillOval',0,...
			[eye.pos(1)-eye.rad eye.pos(2)-eye.rad eye.pos(1)+eye.rad eye.pos(2)+eye.rad]);	
	end; end;
		
 	datain=mean(analin2ch(4,20)); % ie /10*2048.
	eye.pos(1)=round(datain(1)*display.X/2/eye.maxin+display.X/2);
	eye.pos(2)=round(display.Y-datain(2)*display.Y/2/eye.maxin-display.Y/2);
			
	eye.Array(eye.Samples,:)=eye.pos; % storing eye data
	if eye.winrad*eye.winrad>sum(eye.pos.^2), gp.fix.color=3; 
	else gp.fix.color=2; end;
	if isfield(eye,'plotEYEpos'), if eye.plotEYEpos,
		%drawing new eye position
 		SCREEN(display.windowPtr,'FillOval',2,...
			[eye.pos(1)-eye.rad eye.pos(2)-eye.rad eye.pos(1)+eye.rad eye.pos(2)+eye.rad]);	
	end; end;

case 'getEyePosArray',
	if nargout==2, a=eye.Array(1:eye.Samples,:); 
	else error('no output for eye positions provided!');
	end;

otherwise error('bad Eye Tracking command');
end;