function OpenEyesDemo(movieorcamid)

AssertOpenGL;

KbName('UnifyKeyNames');
leftArrow = KbName('LeftArrow');
rightArrow = KbName('RightArrow');
upArrow = KbName('UpArrow');
downArrow = KbName('DownArrow');
rightGUI = KbName('rightGUI');
rightShiftKey = KbName('RightShift');
spaceKey = KbName('space');
calibrateKey = KbName('c');

exposure = 0;

oldPressSecs = 0;
count = 0;
ListenChar(2);

if nargin < 1 || isempty(movieorcamid)
    movieorcamid = 0;
end

try
    winRect = [0 0 800 600];
    winRect = [];
    
    screenid = max(Screen('Screens'));
    oldsync=Screen('Preference', 'SkipSyncTests', 2);
    win = Screen('OpenWindow', screenid, 0, winRect);
    ShowCursor('CrossHair', screenid);
    
    oeyes = PsychOpenEyes('OpenTracker', movieorcamid, win);
    if ~ischar(movieorcamid)
        oldgain = PsychCamSettings('Gain', oeyes)
        gain = PsychCamSettings('Gain', oeyes, 174)
    end
    
    imgtype = 0;
    
    mbuttons = [];
    while ~any(mbuttons) && ~ischar(movieorcamid)
        tex = PsychOpenEyes('GetVideoTexture', oeyes);
        Screen('DrawTexture', win, tex, [], Screen('Rect', tex));
        Screen('Close', tex);

        % Flip at next retrace, but don't do anything to buffers, we'll
        % overwrite anyway:
        Screen('Flip', win, 0, 2);
        [mx, my, mbuttons] = GetMouse(win);
    end        
    
    while 1
        % Show eye image:
        tex = PsychOpenEyes('GetVideoTexture', oeyes);
        Screen('DrawTexture', win, tex, [], Screen('Rect', tex));

        % Flip at next retrace, but don't do anything to buffers, we'll
        % overwrite anyway:
        Screen('Flip', win, 0, 2);

        [clicks, mx, my] = GetClicks(win);
        Screen('DrawTexture', win, tex, [], Screen('Rect', tex));
        Screen('FrameOval', win, [255 255 0], CenterRectOnPoint([0 0 5 5], mx, my), 3, 3);
        Screen('Flip', win, 0, 2);
        mxs = mx;
        mys = my;

        [clicks, mx, my] = GetClicks(win);
        mxe = mx;
        mye = my;
        Screen('DrawTexture', win, tex, [], Screen('Rect', tex));
        eyeRect = [min(mxs, mxe), min(mys, mye), max(mxs, mxe), max(mys, mye)];
        Screen('FrameRect', win, [255 255 0], eyeRect);
        Screen('Flip', win, 0, 2);

        % Release old texture:
        Screen('Close', tex);
        clicks = GetClicks(win);
        if clicks > 1
            break;
        end
    end
    
    minDist = RectWidth(eyeRect) / 8
    maxDist = RectWidth(eyeRect) / 2 * 1.2
%     apprArea = RectWidth(eyeRect)/2 * RectHeight(eyeRect)/2 * pi;
    apprArea = max(RectWidth(eyeRect), RectHeight(eyeRect))/2;
    minArea = apprArea * 0.2
    maxArea = apprArea * 2

    % Set constraints on minimum and maximum distance of features wrt. the
    % pupil center, and on the rough size of the allowable pupil/limbus fit
    % ellipse:
    PsychOpenEyes('SetDynamicConstraints', oeyes, minDist, maxDist, minArea, maxArea);

    % Disable corneal reflection tracking and set a static reference point
    % of (0,0) for visible spectrum eyetracking:
    PsychOpenEyes('SetReferencePoint', oeyes, 0, 0);
    
    tstring = [];
    count = 0;
    
    while 1
        if count == 0
            % First time setup of tracker settings:
            curpar = PsychOpenEyes('TrackerParameters', oeyes);

            % First time invocation: Set a few defaults:
            curpar.eccentricity = 1.1;
            curpar.initialAngleSpread = 36; % This works with visible spectrum imaging.
%            curpar.initialAngleSpread = 45;
            curpar.pupilEdgeThresh = 2;
            curpar.edgeThresh = 16;
            curpar.fanoutAngle1 = 0; %-45;
            curpar.fanoutAngle2 = 180; % 180 + 45;
            curpar.featuresPerRay = 2;
            curpar.specialFlags = +1;
            curpar.rays = 10; %round(curpar.initialAngleSpread * 0.1);
            curpar.gaussWidth = 3;
            % Commit (possibly changed) parameters to tracker:
            PsychOpenEyes('TrackerParameters', oeyes, curpar.pupilEdgeThresh, curpar.rays, curpar.minCand, curpar.corneaWinSize, curpar.edgeThresh, curpar.gaussWidth, curpar.eccentricity, curpar.initialAngleSpread, curpar.fanoutAngle1, curpar.fanoutAngle2, curpar.featuresPerRay, curpar.specialFlags);
        end
        
        % Query mouse:
        [mx, my, mbutton] = GetMouse(win);

        if mbutton(3)
            break;
        end

        if mbutton(1)
            % Wait for next gaze position sample, set new pupil center pos.
            % as starting point for Starburst search:
            eyesample = PsychOpenEyes('GetGazePosition', oeyes, mx, my);
        else
            % Wait for next gaze position sample:
            eyesample = PsychOpenEyes('GetGazePosition', oeyes);
        end

        [keysDown, PressSecs, keyCode] = KbCheck;
        if keysDown && ((PressSecs - oldPressSecs)>0.1)
            dx = 0;
            dy = 0;

            if keyCode(leftArrow)
                dx = -1;
            end

            if keyCode(rightArrow)
                dx = +1;
            end

            if keyCode(downArrow)
                dy = -1;
            end

            if keyCode(upArrow)
                dy = +1;
            end

            % Query current settings:
            curpar = PsychOpenEyes('TrackerParameters', oeyes)
            if ~ischar(movieorcamid)
                exposure = PsychCamSettings('ExposureTime', oeyes);
            end
          
            if keyCode(rightGUI)
                % Change rays or feature candidate parameters:
                curpar.rays = curpar.rays + dx;
                curpar.minCand = curpar.minCand + dy;
            else
                if keyCode(rightShiftKey)
                    % Change cornea search window size:
                    curpar.corneaWinSize = curpar.corneaWinSize + 10*dx;
                    if dy~=0 && ~ischar(movieorcamid)  
                        exposure = exposure + dy/10;
                        PsychCamSettings('ExposureTime', oeyes, exposure);
                    end
                else
                    % Change detection thresholds:
                    curpar.pupilEdgeThresh = curpar.pupilEdgeThresh + dx;
                    curpar.edgeThresh = curpar.edgeThresh + dy;
                end
            end

            if keyCode(spaceKey)
                switch imgtype
                    case 0,
                        imgtype = 2;
                    case 2,
                        imgtype = 3;
                    case 3,
                        imgtype = 4;
                    case 4,
                        imgtype = 0;
                end
            end

            if keyCode(calibrateKey)
                PsychOpenEyes('CalibrateMapping', oeyes);
            end
                        
            % Commit (possibly changed) parameters to tracker:
            PsychOpenEyes('TrackerParameters', oeyes, curpar.pupilEdgeThresh, curpar.rays, curpar.minCand, curpar.corneaWinSize, curpar.edgeThresh, curpar.gaussWidth, curpar.eccentricity, curpar.initialAngleSpread, curpar.fanoutAngle1, curpar.fanoutAngle2, curpar.featuresPerRay, curpar.specialFlags);

            % Clear the framebuffers:
            Screen('Flip', win);

            % Draw text with new tracker settings:
            tstring = sprintf('Pupilthresh: %i , Edgethresh: %i , WinSize: %i , Rays: %i , Cand: %i, Exp: %f \nExcent.: %f , Spread: %f, fanOut1: %f fanOut2: %f \nFeatPerRay: %i sFlags: %i', curpar.pupilEdgeThresh, curpar.edgeThresh, ...
                curpar.corneaWinSize, curpar.rays, curpar.minCand, exposure, curpar.eccentricity, curpar.initialAngleSpread, curpar.fanoutAngle1, curpar.fanoutAngle2, curpar.featuresPerRay, curpar.specialFlags);
            fprintf('%s\n', tstring);
            DrawFormattedText(win, tstring, 0, 485, 255, 240);
            Screen('Flip', win);
            DrawFormattedText(win, tstring, 0, 485, 255, 240);
            Screen('Flip', win, 0, 2);

            % Done with keyboard handling...
            % Keyboard debouncer update:
            oldPressSecs = PressSecs;
            
        end

        % Fetch debug images: This must be after calling 'GetGazePosition',
        % otherwise you'll get stale images from previous cycle!
        tex = PsychOpenEyes('GetTrackerTexture', oeyes, imgtype);

        % Show eye image:
        Screen('DrawTexture', win, tex, [], Screen('Rect', tex));

        Screen('TextSize', win, 24);
        
        % Draw reference point:
        Screen('FillOval', win, [0 255 0], CenterRectOnPoint([0 0 10 10], eyesample.CorneaX, eyesample.CorneaY));
        Screen('DrawText', win, 'CORNEA', eyesample.CorneaX + 5, eyesample.CorneaY + 5, [0 255 0]);
        
        % Draw pupil point:
        Screen('FillOval', win, [0 255 255], CenterRectOnPoint([0 0 10 10], eyesample.PupilX, eyesample.PupilY));
        Screen('DrawText', win, 'PUPIL', eyesample.PupilX + 5, eyesample.PupilY + 5, [0 255 255]);

        % Valid tracking result with calibrated gaze point?
        if eyesample.Valid > 0
            % Draw point of gaze:
            Screen('FillOval', win, [255 255 0], CenterRectOnPoint([0 0 10 10], eyesample.GazeX, eyesample.GazeY));
            Screen('FrameRect', win, [255 255 0], CenterRectOnPoint([0 0 10 10], eyesample.GazeX, eyesample.GazeY));
            Screen('DrawText', win, 'GAZE', eyesample.GazeX + 5, eyesample.GazeY + 5, [255 255 0]);
        end

        if ~isempty(tstring) DrawFormattedText(win, tstring, 0, 485, 255, 240); end

        % Flip at next retrace, but don't do anything to buffers, we'll
        % overwrite anyway:
        Screen('Flip', win, 0, 0);

        % Release old texture:
        Screen('Close', tex);

        % Print out tracking results:
        %disp(eyesample);

        if ischar(movieorcamid)
            KbWait;
            WaitSecs(0.2);
        end
      
        % Ready for next iteration...
        count = count + 1;
    end

    PsychOpenEyes('CloseTracker', oeyes);
    ShowCursor('Arrow', screenid);
    sca;
    ListenChar(0);
    Screen('Preference', 'SkipSyncTests', oldsync);
    return;
catch
    ListenChar(0);
    if exist('oeyes', 'var')
      PsychOpenEyes('CloseTracker', oeyes);
    end
    
    ShowCursor('Arrow', screenid);
    sca;
    Screen('Preference', 'SkipSyncTests', oldsync);
    psychrethrow(psychlasterror);
    return;
end
