<!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" xml:lang="en" lang="en">
<head>
<title>libQGLViewer frameTransform example</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<link href="../qglviewer.css" rel="stylesheet" type="text/css" />
<link rel="shortcut icon" href="../images/qglviewer.ico" type="image/x-icon" />
<link rel="icon" href="../images/qglviewer.icon.png" type="image/png" />
</head>
<body>
<table class="banner">
<tr>
<td align="center"><a href="../index.html"><b>Home</b></a></td>
<td align="center"><a href="../refManual/hierarchy.html"><b>Documentation</b></a></td>
<td align="center"><a href="../download.html"><b>Download</b></a></td>
<td align="center" class="qindexHL"><a href="index.html"><b>Screenshots</b></a></td>
<td align="center"><a href="../developer.html"><b>Developer</b></a></td>
</tr>
</table>
<h1>The frameTransform example</h1>
<center>
<img src="../images/frameTransform.jpg" width="300" height="200" alt="frameTransform"/>
</center>
<p>
Coordinate transformation between different Frames.
</p>
<p>
This example illustrates the camera and world coordinate systems
relationship. The position of the camera in the world coordinate
system is printed from Camera::position(). Symetrically, the
position of the world origin is given in the camera coordinate
system by camera()->cameraCoordinatesOf(0,0,0).
</p>
<p>
Three sets of lines (red, green, blue) are drawned. They have different starting points, but
common end points, located on a circle in the XY plane.
</p>
<p>
All the red lines start from the camera position, and will hence always be aligned with the
viewing direction, making them invisible.
</p>
<p>
The green lines starting points' positions are determined from the camera coordinate system, using
<code>camera()->worldCoordinatesOf()</code>. As a result, these points will seem to be fixed on
the screen, even when the camera is moved
</p>
<p>
Finally, the blue lines are classically defined in the world coordinate system, and will move with
the camera.
</p>
<p>
Beautiful Moire pattern can be obtained with a proper rotation.
</p>
<h2>frameTransform.h</h2>
<pre>
<span class="dir">#include <QGLViewer/qglviewer.h>
</span>
<span class="key">class </span>Viewer : <span class="key">public </span>QGLViewer
{
<span class="key">protected </span>:
<span class="key">virtual </span><span class="typ">void </span>draw();
<span class="key">virtual </span><span class="typ">void </span>init();
<span class="key">virtual </span>QString helpString() <span class="typ">const</span>;
};</pre>
<h2>frameTransform.cpp</h2>
<pre>
<span class="dir">#include </span><span class="dstr">"frameTransform.h"</span><span class="dir">
</span>
<span class="key">using namespace </span>std;
<span class="key">using namespace </span>qglviewer; <span class="com">// Vec
</span>
<span class="typ">void </span>Viewer::init()
{
restoreFromFile();
setSceneRadius(<span class="num">1.5</span>);
showEntireScene();
setDrawAxis();
glDisable(GL_LIGHTING);
help();
}
<span class="typ">void </span>Viewer::draw()
{
<span class="com">// Draws line sets (red, green, blue) with different origins, but with a common
</span> <span class="com">// end point, located on a circle in the XY plane.
</span> <span class="typ">const float </span>nbLines = <span class="num">50.0</span>;
glBegin(GL_LINES);
<span class="key">for </span>(<span class="typ">float </span>i=<span class="num">0</span>; i<nbLines; ++i)
{
<span class="typ">float </span>angle = <span class="num">2.0</span>*M_PI*i/nbLines;
glColor3f(.<span class="num">8</span>,.<span class="num">2</span>,.<span class="num">2</span>);
<span class="com">// These lines will never be seen as they are always aligned with the viewing direction.
</span> glVertex3fv(camera()->position().address());
glVertex3f (cos(angle), sin(angle), <span class="num">0.0</span>);
glColor3f(.<span class="num">2</span>,.<span class="num">8</span>,.<span class="num">2</span>);
<span class="com">// World Coordinates are infered from the camera, and seem to be immobile in the screen.
</span> glVertex3fv(camera()->worldCoordinatesOf(Vec(.<span class="num">3</span>*cos(angle), .<span class="num">3</span>*sin(angle), <span class="num">-2.0</span>)).address());
glVertex3f (cos(angle), sin(angle), <span class="num">0.0</span>);
glColor3f(.<span class="num">2</span>,.<span class="num">2</span>,.<span class="num">8</span>);
<span class="com">// These lines are defined in the world coordinate system and will move with the camera.
</span> glVertex3f(<span class="num">1.5</span>*cos(angle), <span class="num">1.5</span>*sin(angle), <span class="num">-1.0</span>);
glVertex3f(cos(angle), sin(angle), <span class="num">0.0</span>);
}
glEnd();
Vec origin = camera()->cameraCoordinatesOf(Vec(<span class="num">0.0</span>, <span class="num">0.0</span>, <span class="num">0.0</span>));
cout << <span class="str">"Camera position in world coord. system = "</span> << camera()->position() << endl;
cout << <span class="str">"World origin position in camera frame = "</span> << origin << endl;
cout << endl;
}
QString Viewer::helpString() <span class="typ">const
</span>{
QString text(<span class="str">"<h2>F r a m e T r a n s f o r m</h2>"</span>);
text += <span class="str">"This example illustrates how easy it is to switch between the camera and "</span>;
text += <span class="str">"the world coordinate systems : using the <i>camera()->cameraCoordinatesOf()</i> "</span>;
text += <span class="str">"and <i>camera::worldCoordinatesOf()</i> functions.<br>"</span>;
text += <span class="str">"You can create your own hierarchy of local coordinates systems and each of "</span>;
text += <span class="str">"them can be manipulated with the mouse (see the <i>manipulatedFrame</i> and <i>luxo</i> examples). "</span>;
text += <span class="str">"Standard functions allow you to convert from any local frame to an other, "</span>;
text += <span class="str">"the world/camera relation presented here simply being one of its illustration.<br>"</span>;
text += <span class="str">"See <i>examples/frameTransform.html</i> for an explanation of the meaning of these weird lines."</span>;
<span class="key">return </span>text;
}
</pre>
<h2>main.cpp</h2>
<pre>
<span class="dir">#include </span><span class="dstr">"frameTransform.h"</span><span class="dir">
</span><span class="dir">#include <qapplication.h>
</span>
<span class="typ">int </span>main(<span class="typ">int </span>argc, <span class="typ">char</span>** argv)
{
<span class="com">// Read command lines arguments.
</span> QApplication application(argc,argv);
<span class="com">// Instantiate the viewer.
</span> Viewer v;
<span class="com">// Make the viewer window visible on screen.
</span> v.show();
<span class="com">// Set the viewer as the application main widget.
</span> application.setMainWidget(&v);
<span class="com">// Run main loop.
</span> <span class="key">return </span>application.exec();
}</pre>
<p>
<a href="index.html">Go back</a> to the examples main page
</p>
<p>
<a href="http://validator.w3.org/check/referer"><img src="../images/xhtml.png" alt="Valid XHTML 1.0!" height="31" width="88" border="0"/></a>
<a href="http://jigsaw.w3.org/css-validator/check/referer"><img src="../images/css.png" width="88" height="31" alt="Valid CSS!" border="0"/></a>
<i>Last modified on Thursday, February 5, 2004.</i>
</p>
</body>
</html>
