<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <html> <head> <link rel="STYLESHEET" href="visionegg.css" type='text/css' /> <link rel='start' href='http://www.visionegg.org/' title='Vision Egg website' /> <link rel="first" href="visionegg.html" title='The Vision Egg Programmer's Manual' /> <link rel='contents' href='contents.html' title="Contents" /> <link rel='last' href='about.html' title='About this document...' /> <link rel='help' href='about.html' title='About this document...' /> <link rel="next" href="node6.html" /> <link rel="prev" href="hierarchy.html" /> <link rel="parent" href="visionegg.html" /> <link rel="next" href="node6.html" /> <meta name='aesop' content='information' /> <title>3. Controlling stimulus parameters in realtime </title> </head> <body> <DIV CLASS="navigation"> <div id='top-navigation-panel' xml:id='top-navigation-panel'> <table align="center" width="100%" cellpadding="0" cellspacing="2"> <tr> <td class='online-navigation'><a rel="prev" title="2. Hierarchy of graphical" href="hierarchy.html"><img src='../images/previous.png' border='0' height='32' alt='Previous Page' width='32' /></A></td> <td class='online-navigation'><a rel="parent" title="The Vision Egg Programmer's" href="visionegg.html"><img src='../images/up.png' border='0' height='32' alt='Up One Level' width='32' /></A></td> <td class='online-navigation'><a rel="next" title="4. Other general information" href="node6.html"><img src='../images/next.png' border='0' height='32' alt='Next Page' width='32' /></A></td> <td align="center" width="100%">The Vision Egg Programmer's Manual</td> <td class='online-navigation'><a rel="contents" title="Table of Contents" href="contents.html"><img src='../images/contents.png' border='0' height='32' alt='Contents' width='32' /></A></td> <td class='online-navigation'><img src='../images/blank.png' border='0' height='32' alt='' width='32' /></td> <td class='online-navigation'><img src='../images/blank.png' border='0' height='32' alt='' width='32' /></td> </tr></table> <div class='online-navigation'> <b class="navlabel">Previous:</b> <a class="sectref" rel="prev" href="hierarchy.html">2. Hierarchy of graphical</A> <b class="navlabel">Up:</b> <a class="sectref" rel="parent" href="visionegg.html">The Vision Egg Programmer's</A> <b class="navlabel">Next:</b> <a class="sectref" rel="next" href="node6.html">4. Other general information</A> </div> <hr /></div> </DIV> <!--End of Navigation Panel--> <H1><A NAME="SECTION005000000000000000000"></A><A NAME="controllers"></A> <BR> 3. Controlling stimulus parameters in realtime </H1> <P> When using the <tt class="class">Presentation</tt> class, you have a powerful method of updating parameters in realtime available to you. ``Controllers'' are instances of the class <tt class="class">Controller</tt>. A controller is called at pre-defined intervals and updates the value of some stimulus parameter. For example, in the ``target'' demo script, the ``center'' parameter of a <tt class="class">Target2D</tt> stimulus is updated on every frame by a function which computes position based upon the current time. You can also control parameters without using controllers by simply changing the values as your program executes. <P> Instances of <tt class="class">Controller</tt> are called by instances of the <tt class="class">Presentation</tt> class. After creating an instance of <tt class="class">Controller</tt>, it must be ``registered'' by calling the <tt class="method">add_controller</tt> method of <tt class="class">Presentation</tt>, during which the stimulus parameter under control is specified. The <tt class="class">Presentation</tt> takes care of calling the controller from this point. Specifically, the <tt class="method">during_go_eval()</tt> is called during a <tt class="method">go()</tt> loop, and <tt class="method">between_go_eval()</tt> is called by <tt class="method">between_presentations()</tt> (during <tt class="method">run_forever()</tt>, for example.) These ``eval'' methods return a value which becomes the new value of the parameter being controller. <P> The frequency with which <tt class="method">during_go_eval()</tt> and <tt class="method">between_go_eval()</tt> are evaluated is determined by the <var>eval_frequency</var> attribute of the controller. The default <var>eval_frequency</var> is every frame. <P> The <var>temporal_variables</var> attribute of the controller specifies what temporal variables the ``eval'' methods have available to base calculations on. The default value is TIME_SEC_SINCE_GO, so when <tt class="method">during_go_eval()</tt> is called, the instance will have an attribute <var>time_sec_since_go</var> set to the time since the onset of the <tt class="method">go()</tt> loop. <P> For more information, see the documentation for the <tt class="class">Controller</tt> and <tt class="class">Presentation</tt> classes in the <tt class="module">VisionEgg.Core</tt> module. <P> <DIV CLASS="navigation"> <div class='online-navigation'> <p></p><hr /> <table align="center" width="100%" cellpadding="0" cellspacing="2"> <tr> <td class='online-navigation'><a rel="prev" title="2. Hierarchy of graphical" href="hierarchy.html"><img src='../images/previous.png' border='0' height='32' alt='Previous Page' width='32' /></A></td> <td class='online-navigation'><a rel="parent" title="The Vision Egg Programmer's" href="visionegg.html"><img src='../images/up.png' border='0' height='32' alt='Up One Level' width='32' /></A></td> <td class='online-navigation'><a rel="next" title="4. Other general information" href="node6.html"><img src='../images/next.png' border='0' height='32' alt='Next Page' width='32' /></A></td> <td align="center" width="100%">The Vision Egg Programmer's Manual</td> <td class='online-navigation'><a rel="contents" title="Table of Contents" href="contents.html"><img src='../images/contents.png' border='0' height='32' alt='Contents' width='32' /></A></td> <td class='online-navigation'><img src='../images/blank.png' border='0' height='32' alt='' width='32' /></td> <td class='online-navigation'><img src='../images/blank.png' border='0' height='32' alt='' width='32' /></td> </tr></table> <div class='online-navigation'> <b class="navlabel">Previous:</b> <a class="sectref" rel="prev" href="hierarchy.html">2. Hierarchy of graphical</A> <b class="navlabel">Up:</b> <a class="sectref" rel="parent" href="visionegg.html">The Vision Egg Programmer's</A> <b class="navlabel">Next:</b> <a class="sectref" rel="next" href="node6.html">4. Other general information</A> </div> </div> <hr /> <span class="release-info">Release 1.1.1, documentation updated on September 7, 2008.</span> </DIV> <!--End of Navigation Panel--> </BODY> </HTML>
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