Using rectangle function in gui, not getting displayed?

I have created a gui to insert video stream from webcam based on the code from

http://www.mathworks.com/matlabcentral/answers/96242-how-can-i-insert-live-video-into-a-matlab-gui-using-image-acquisition-toolbox

I have previously used rectangle function in normal figures with imshow and hold on, to put bounding boxes to track human. Now I want to use the rectangle function in gui. I tried displaying in a small while loop for testing. But Im not getting it.

Code:

function myCameraGUI_OpeningFcn(hObject, eventdata, handles, varargin)

handles.output = hObject;

handles.video = videoinput('winvideo', 2);

set(handles.video,'TimerPeriod', 0.05, ...
'TimerFcn',['if(~isempty(gco)),'...
'handles=guidata(gcf);'... % Update handles
'image(getsnapshot(handles.video));'... % Get picture using GETSNAPSHOT and put it into axes using IMAGE
'set(handles.cameraAxes,''ytick'',[],''xtick'',[]),'... % Remove tickmarks and labels that are inserted when using IMAGE
'else '...
'delete(imaqfind);'... % Clean up - delete any image acquisition objects
'end']);
triggerconfig(handles.video,'manual');
handles.video.FramesPerTrigger = Inf; % Capture frames until we manually stop it

% Update handles structure
guidata(hObject, handles);

% UIWAIT makes mycameragui wait for user response (see UIRESUME)
uiwait(handles.myCameraGUI);

%------
%Callback Fn for startCamera Button
function startStopCamera_Callback(hObject, eventdata, handles)

if strcmp(get(handles.startStopCamera,'String'),'Start Camera')
    % Camera is off. Change button string and start camera.
    set(handles.startStopCamera,'String','Stop Camera')

      start(handles.video)

      i=1;
      x3=500;
      y3=300;
      while(i<20)

          rectangle('Position',[x3,y3,10,10],'EdgeColor','r','LineWidth',1);
          i=i+1
      end

else
    % Camera is on. Stop camera and change button string.
    set(handles.startStopCamera,'String','Start Camera')
    stop(handles.video)

end

Answer 1

[Walter Roberson]

Where is your drawnow() ?

Why are you drawing 20 rectangles in the same position on the same frame?

Which figure or axes are you drawing the rectangles in?

[Avinash S]

drawnow was the cause. thank you @Walter Robertson. I just wanted to check thats why i<20. And its not the same frame, It displays frames streaming from webcam