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<title>libQGLViewer triSetConstraint example</title>
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<h1>The triSetConstraint example</h1>
<center>
<img src="../images/triSetConstraint.jpg" width="300" height="200" alt="triSetConstraint"/>
</center>
<p>
A <code>TriangleSetConstraint</code> constrains the camera displacement.
</p>
<p>
The camera is constrained to stay above a given 'road' defined
by triangles. Camera is in FLY mode.
</p>
<p>
The example is a little bit complex : the computations needed
to get the intersection of the Z-direction and the triangle are
cut and pasted from the triangleSetConstraint class, in order to
draw interesting debugging informations.
</p>
<h2>triSetConstraint.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="typ">void </span>init();
<span class="typ">void </span>draw();
<span class="typ">void </span>displayConstraint(qglviewer::Vec);
};</pre>
<h2>triSetConstraint.cpp</h2>
<pre>
<span class="dir">#include </span><span class="dstr">"triSetConstraint.h"</span><span class="dir">
</span><span class="dir">#include <QGLViewer/triangleSetConstraint.h>
</span><span class="dir">#include <math.h>
</span>
<span class="key">using namespace </span>qglviewer;
<span class="typ">static bool </span>segmentIntersection(<span class="typ">const </span>Vec& p, <span class="typ">const </span>Vec& dir1, <span class="typ">const </span>Vec& norm,
<span class="typ">const </span>Vec& s1, <span class="typ">const </span>Vec& s2,
Vec& inter)
{
<span class="com">// dir1 is supposed to be normalized.
</span> Vec perp = cross(dir1, norm);
<span class="com">// Check for near-parallel lines
</span> <span class="typ">float </span>n = perp.norm();
<span class="com">// Degenerated case : parallel lines
</span> <span class="key">if </span>(n < <span class="num">1.E</span>-<span class="num">10</span>)
<span class="key">return false</span>;
perp /= n;
<span class="typ">float </span>proj = (s2 - s1) * perp;
<span class="typ">float </span>alpha = ((p-s1)*perp) / proj;
<span class="key">if </span>( (alpha < <span class="num">0.0</span>) || (alpha > <span class="num">1.0</span>) )
<span class="key">return false</span>;
<span class="com">// else
</span> inter = s1 + (s2-s1) * alpha;
<span class="key">return true</span>;
}
<span class="com">/* Constrain the translation \p trans with respect to a path defined by a triangle set. See addTriangle() and addPoint(). */</span>
<span class="typ">void </span>Viewer::displayConstraint(Vec trans)
{
TriangleSetConstraint* tsc = (TriangleSetConstraint*)(camera()->frame()->constraint());
<span class="typ">unsigned int </span>currentTriangle = tsc->currentTriangle();
trans = camera()->frame()->inverseTransformOf(trans);
Vec pos, nextPos, start;
start = camera()->position();
pos = start;
<span class="typ">unsigned short </span>nextEdge;
<span class="typ">const float </span>dist = trans.norm();
<span class="key">if </span>(dist < <span class="num">1E</span>-<span class="num">8</span>)
<span class="key">return</span>;
trans /= dist;
<span class="com">// Draw the current triangle
</span> glColor3f(.<span class="num">6</span>,.<span class="num">2</span>,<span class="num">6</span>);
glLineWidth(<span class="num">4.0</span>);
glBegin(GL_TRIANGLES);
glVertex3fv(tsc->point(tsc->trianglePoint(currentTriangle,<span class="num">0</span>)).address());
glVertex3fv(tsc->point(tsc->trianglePoint(currentTriangle,<span class="num">1</span>)).address());
glVertex3fv(tsc->point(tsc->trianglePoint(currentTriangle,<span class="num">2</span>)).address());
glEnd();
glColor3f(.<span class="num">8</span>,.<span class="num">5</span>,<span class="num">0</span>);
glPointSize(<span class="num">10.0</span>);
glBegin(GL_POINTS); glVertex3fv(start.address()); glEnd();
glLineWidth(<span class="num">1.0</span>);
glBegin(GL_LINES); glVertex3fv(start.address()); glVertex3fv((start+trans).address()); glEnd();
glColor3f(.<span class="num">4</span>,.<span class="num">6</span>,.<span class="num">7</span>);
glPointSize(<span class="num">5.0</span>);
<span class="key">while </span>(<span class="key">true</span>)
{
<span class="typ">float </span>step = <span class="num">-1.0E9f</span>;
nextEdge = <span class="num">3</span>;
Vec e1 = tsc->point(tsc->trianglePoint(currentTriangle,<span class="num">0</span>)) - tsc->point(tsc->trianglePoint(currentTriangle,<span class="num">1</span>));
Vec e2 = tsc->point(tsc->trianglePoint(currentTriangle,<span class="num">0</span>)) - tsc->point(tsc->trianglePoint(currentTriangle,<span class="num">2</span>));
Vec norm = cross(e1, e2);
Vec res;
<span class="key">for </span>(<span class="typ">unsigned short </span>edge=<span class="num">0</span>; edge<<span class="num">3</span>; edge++)
{
<span class="key">if </span>(segmentIntersection(pos, trans, norm,
tsc->point(tsc->trianglePoint(currentTriangle,(edge+<span class="num">1</span>)%<span class="num">3</span>)),
tsc->point(tsc->trianglePoint(currentTriangle,(edge+<span class="num">2</span>)%<span class="num">3</span>)), res))
{
<span class="key">if </span>((res-pos)*trans > step)
{
step = (res-pos)*trans;
nextPos = res;
nextEdge = edge;
}
}
}
glBegin(GL_POINTS); glVertex3fv(nextPos.address()); glEnd();
<span class="typ">float </span>soFar = (nextPos-start)*trans;
<span class="key">if </span>((soFar > dist) || (tsc->neighTriangle(currentTriangle,nextEdge) == <span class="num">-1</span>))
<span class="key">return</span>;
currentTriangle = tsc->neighTriangle(currentTriangle,nextEdge);
pos = nextPos;
}
}
<span class="typ">static const float </span>nbSteps = <span class="num">20.0</span>;
<span class="typ">static const float </span>r = <span class="num">0.7</span>;
<span class="typ">void </span>Viewer::init()
{
setSceneRadius(<span class="num">3.0</span>);
camera()->setFlySpeed(<span class="num">0.001</span>);
<span class="com">// Use fly mode mouse bindings
</span> toggleCameraMode();
glPolygonMode(GL_FRONT_AND_BACK,GL_LINE);
TriangleSetConstraint* tsc = <span class="key">new </span>TriangleSetConstraint();
camera()->frame()->setConstraint(tsc);
tsc->addPoint(Vec(<span class="num">1.0</span>,<span class="num">0.0</span>,<span class="num">0.0</span>));
tsc->addPoint(Vec(r ,<span class="num">0.0</span>,<span class="num">0.0</span>));
<span class="key">for </span>(<span class="typ">int </span>i=<span class="num">1</span>; i<nbSteps; ++i)
{
<span class="typ">float </span>angle = <span class="num">2.0 </span>* M_PI * i / nbSteps;
tsc->addPoint(Vec(cos(angle) , sin(angle) , <span class="num">0.0</span>)); <span class="com">// index 2i
</span> tsc->addPoint(Vec(r*cos(angle), r*sin(angle), <span class="num">0.0</span>)); <span class="com">// index 2i+1
</span>
tsc->addTriangle(<span class="num">2</span>*i-1, <span class="num">2</span>*i, <span class="num">2</span>*i+<span class="num">1</span>);
tsc->addTriangle(<span class="num">2</span>*i-1, <span class="num">2</span>*i-2, <span class="num">2</span>*i);
}
tsc->addTriangle(<span class="num">0</span>, <span class="num">2</span>*(<span class="typ">int</span>)nbSteps-2, <span class="num">2</span>*(<span class="typ">int</span>)nbSteps-1);
tsc->addTriangle(<span class="num">0</span>, <span class="num">1</span>, <span class="num">2</span>*(<span class="typ">int</span>)nbSteps-1);
tsc->setCurrentTriangle(<span class="num">1</span>);
camera()->setOrientation(Quaternion(Vec(<span class="num">1</span>,<span class="num">0</span>,<span class="num">0</span>), M_PI/<span class="num">2.0</span>));
camera()->setPosition(<span class="num">0.85</span>, <span class="num">0.05</span>, <span class="num">0.0</span>);
}
<span class="typ">void </span>Viewer::draw()
{
<span class="com">// The camera is made visible by reseting the modelview matrix
</span> glLoadIdentity();
glTranslatef(<span class="num">0.0</span>,<span class="num">0.0</span>,<span class="num">-2.5</span>);
<span class="com">// Draw Road
</span> glNormal3f(<span class="num">0.0</span>, <span class="num">0.0</span>, <span class="num">1.0</span>);
glColor3f(.<span class="num">2</span>,.<span class="num">6</span>,.<span class="num">8</span>);
glBegin(GL_QUAD_STRIP);
<span class="key">for </span>(<span class="typ">float </span>i=<span class="num">0</span>; i<=nbSteps; ++i)
{
<span class="typ">float </span>angle = <span class="num">2.0 </span>* M_PI * i / nbSteps;
glVertex3f(cos(angle), sin(angle), <span class="num">0.0</span>);
glVertex3f(r*cos(angle), r*sin(angle), <span class="num">0.0</span>);
}
glEnd();
<span class="com">// Draw camera position
</span> Vec pos = camera()->position();
glPointSize(<span class="num">5.0</span>);
glBegin(GL_POINTS);
glVertex3fv(pos.address());
glEnd();
displayConstraint(Vec(<span class="num">0</span>,<span class="num">0</span>,<span class="num">-1</span>));
}
</pre>
<h2>main.cpp</h2>
<pre>
<span class="dir">#include </span><span class="dstr">"triSetConstraint.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>
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<i>Last modified on Friday, November 7, 2003.</i>
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