:param value:The optional pointer to an integer variable, whose value will reflect the position of the slider. Upon creation, the slider position is defined by this variable.
:param onChange:Pointer to the function to be called every time the slider changes position. This function should be prototyped as ``void Foo(int,void*);`` , where the first parameter is the trackbar position and the second parameter is the user data (see the next parameter). If the callback is NULL pointer, then no callbacks is called, but only ``value`` is updated
:param userdata:The user data that is passed as-is to the callback; it can be used to handle trackbar events without using global variables
The function ``createTrackbar`` creates a trackbar (a.k.a. slider or range control) with the specified name and range, assigns a variable ``value`` to be syncronized with trackbar position and specifies a callback function ``onChange`` to be called on the trackbar position change. The created trackbar is displayed on the top of the given window.
***winname** Name of the window which will be used as a parent for created trackbar. Can be NULL if the trackbar should be attached to the control panel.
The function ``imshow`` displays the image in the specified window. If the window was created with the ``CV_WINDOW_AUTOSIZE`` flag then the image is shown with its original size, otherwise the image is scaled to fit in the window. The function may scale the image, depending on its depth:
:param flags:Flags of the window. Currently the only supported flag is ``CV_WINDOW_AUTOSIZE`` . If this is set, the window size is automatically adjusted to fit the displayed image (see :ref:`imshow` ), and the user can not change the window size manually.
The function ``namedWindow`` creates a window which can be used as a placeholder for images and trackbars. Created windows are referred to by their names.
***CV_WINDOW_NORMAL or CV_WINDOW_AUTOSIZE:**``CV_WINDOW_NORMAL`` let the user resize the window, whereas ``CV_WINDOW_AUTOSIZE`` adjusts automatically the window's size to fit the displayed image (see :ref:`imshow` ), and the user can not change the window size manually.
***CV_WINDOW_FREERATIO or CV_WINDOW_KEEPRATIO:**``CV_WINDOW_FREERATIO`` adjust the image without respect the its ration, whereas ``CV_WINDOW_KEEPRATIO`` keep the image's ratio.
***CV_GUI_NORMAL or CV_GUI_EXPANDED:**``CV_GUI_NORMAL`` is the old way to draw the window without statusbar and toolbar, whereas ``CV_GUI_EXPANDED`` is the new enhance GUI.
The function ``waitKey`` waits for key event infinitely (when
:math:`\texttt{delay}\leq 0` ) or for ``delay`` milliseconds, when it's positive. Returns the code of the pressed key or -1 if no key was pressed before the specified time had elapsed.
This function is the only method in HighGUI that can fetch and handle events, so it needs to be called periodically for normal event processing, unless HighGUI is used within some environment that takes care of event processing.
**Note 2:**
The function only works if there is at least one HighGUI window created and the window is active. If there are several HighGUI windows, any of them can be active.
