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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"><!-- InstanceBegin template="/Templates/template.dwt" codeOutsideHTMLIsLocked="false" -->
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<!-- InstanceBeginEditable name="doctitle" -->
<title>trail</title>
<!-- InstanceEndEditable -->
<!-- InstanceBeginEditable name="head" -->
<link href="VisualRef.css" rel="stylesheet" type="text/css" />
<style type="text/css">
<!--
.style1 {font-size: x-large}
.style2 {font-size: xx-large}
-->
</style>
<!-- InstanceEndEditable -->
<script type="text/javascript">
<!--
function MM_jumpMenu(targ,selObj,restore){ //v3.0
eval(targ+".location='"+selObj.options[selObj.selectedIndex].value+"'");
if (restore) selObj.selectedIndex=0;
}
//-->
</script>
<link href="VisualRef.css" rel="stylesheet" type="text/css" />
</head>
<body>
<table width="800" border="0" cellpadding="0" cellspacing="0">
<!--DWLayoutDefaultTable-->
<tr>
<td width="10" valign="top" bgcolor="#FFFFFF"><!--DWLayoutEmptyCell--> </td>
<td width="10" height="272" valign="top" bgcolor="#DDDDDD"><p> </p> </td>
<td width="173" valign="top" bgcolor="#DDDDDD"><p class="Normal"><a href="index.html">Home</a></p>
<p class="Normal">If you're new to Python <br />
and VPython: <a href="VisualIntro.html">Introduction</a></p>
<p class="Normal">A VPython <a href="VPython_Intro.pdf" target="_blank">tutorial</a></p>
<p class="Normal"><a href="primitives.html">Pictures</a> of 3D objects</p>
<p class="Normal">Choose an object:</p>
<select name="jumpMenu4" id="jumpMenu4" onchange="MM_jumpMenu('parent',this,0)">
<option>Choose an object</option>
<option value="cylinder.html">Overview</option>
<option value="arrow.html">arrow</option>
<option value="box.html">box</option>
<option value="cone.html">cone</option>
<option value="convex.html">convex</option>
<option value="curve.html">curve</option>
<option value="cylinder.html">cylinder</option>
<option value="ellipsoid.html">ellipsoid</option>
<option value="extrusion.html">extrusion</option>
<option value="faces.html">faces</option>
<option value="frame.html">frame</option>
<option value="helix.html">helix</option>
<option value="label.html">label</option>
<option value="lights.html">lights</option>
<option value="points.html">points</option>
<option value="pyramid.html">pyramid</option>
<option value="ring.html">ring</option>
<option value="sphere.html">sphere</option>
<option value="text.html">text</option>
</select>
<p class="Normal">Work with objects:</p>
<select name="jumpMenu4" id="jumpMenu5" onchange="MM_jumpMenu('parent',this,0)">
<option>Choose an option</option>
<option value="color.html">Color/Opacity</option>
<option value="materials.html">Materials/Textures</option>
<option value="shapes.html">Shapes Library</option>
<option value="paths.html">Paths Library</option>
<option value="defaults.html">Defaults</option>
<option value="rate.html">Animation Speed</option>
<option value="rotation.html">Rotations</option>
<option value="options.html">Additional Options</option>
<option value="delete.html">Delete an Object</option>
<option value="float.html">3/4 = 0?</option>
<option value="controls.html">Buttons/Sliders</option>
<option value="graph.html">Graphs</option>
<option value="lights.html">Lighting</option>
<option value="files.html">Read/Write Files</option>
<option value="trail.html">Leaving a Trail</option>
<option value="vector.html">Vector Operations </option>
<option value="factorial.html">factorial/combin</option>
</select>
<p class="Normal">Windows & Events:</p>
<select name="jumpMenu4" id="jumpMenu6" onchange="MM_jumpMenu('parent',this,0)">
<option>Choose a topic</option>
<option value="display.html">Windows</option>
<option value="mouse.html">Mouse Events</option>
<option value="mouse_click.html"> Mouse Click</option>
<option value="mouse_drag.html"> Mouse Drag</option>
<option value="keyboard.html">Keyboard Events</option>
</select>
<p class="Normal">What's new in <a href="new_features.html">Visual 5</a></p>
<p class="Normal"><a href="http://vpython.org" target="_blank">VPython web site</a><br />
<a href="license.txt" target="_blank">Visual license</a><br />
<a href="http://www.python.org" target="_blank">Python web site</a> <br />
<a href="http://www.python.org/doc/2.5.2/lib/module-math.html" target="_blank">Math module</a> (sqrt etc.)<br />
<a href="http://www.scipy.org/Documentation" target="_blank">Numpy module</a> (arrays) </p></td>
<td width="21" valign="top" bgcolor="#FFFFFF"><!--DWLayoutEmptyCell--> </td>
<td width="586" rowspan="2" valign="top"><!-- InstanceBeginEditable name="content" -->
<div>
<table width="100%" border="1">
<tr>
<td width="77%"><div align="center"><span class="style1 style2"><font color="#0000A0">Leaving a Trail</font></span></div></td>
<td width="23%"><div align="center"><img src="images/trail.jpg" width="414" height="113" alt="trails" /><a href="arrow.html"></a></div></td>
</tr>
</table>
</div>
<div>
<p class="Normal"> You can leave a trail behind a moving object simply by specifying <span class="attribute">make_trail=True</span>:</p>
<div>
<p class="program"> ball = sphere(make_trail=True)</p>
<p class="Normal"> Each time you change <span class="attribute">ball.pos</span>, this new position is added to a curve, thereby leaving a trail behind the moving sphere. This works with arrow, box, cone, cylinder, ellipsoid, pyramid, ring, and sphere.</p>
<p class="Normal">You can specify using a points object rather than a curve object for displaying the trail, and you can specify how many points to skip or retain:</p>
<p class="program"> ball = sphere(make_trail=True, trail_type="points",<br />
interval=10, retain=50)</p>
<p class="Normal">The trail of this sphere will show individual points rather than a continuous line, it will display points at every 10th sphere location, and it will retain only the most recent 50 of these points.</p>
<p class="Normal">At any time during the moving of the object, you can specify <span class="attribute">ball.make_trail=False</span>, in which case no more points are added to the ball's trail until you set <span class="attribute">ball.make_trail=False</span> again. Note however that with the default <span class="attribute">trail_type="curve"</span>, when you resume adding points to the curve there will be a line drawn from the last location to the current location.</p>
<p class="Normal">When you create a sphere with <span class="attribute">make_trail=True</span> or <span class="attribute">make_trail=False</span>, a curve or points object is created as a <span class="attribute">trail_objec</span>t attribute of the sphere object. If you say <span class="attribute">ball.trail_object.color=color.orange</span>, you will change the color of the curve or points to orange.</p>
<p class="Normal"><strong><font color="#0000a0">Summary</font></strong></p>
<p class="attributes"> <span class="attribute">make_trail</span> Must be mentioned when creating the moving object; if False, no points will be added to the trail until you say <span class="attribute">ball.make_rail = True</span> (assuming the moving object is named ball)</p>
<p class="attributes"> <span class="attribute">trail_type</span> Default is "curve", but can be "points"</p>
<p class="attributes"> <span class="attribute">interval</span> If interval=10, a point is added to the trail only every 10th move of the object</p>
<p class="attributes"> <span class="attribute">retain</span> If retain=50, only the 50 most recently added points will be retained </p>
<p class="attributes"> <span class="attribute">trail_object</span> The curve or points object; <span class="Normal"><span class="attribute">ball.trail_object.color=color.orange</span> will change the color of the trail to orange</span></p>
<!-- InstanceEndEditable --></td>
</tr>
<tr>
<td height="16" colspan="4"></td>
</tr>
</table>
</body>
<!-- InstanceEnd --></html>