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<div align="left"><b><font color="#FFFFFF">Tutorial 7. Collision detection
and response</font></b></div>
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<p>In this tutorial, I will show how to collision detection with the Irrlicht
Engine. I will describe 3 methods: Automatic collision detection for
moving through 3d worlds with stair climbing and sliding, manual triangle
picking and manual scene node picking.</p>
<p>The program which is described here will look like this:</p>
<p align="center"><img src="../../media/007shot.jpg" width="259" height="204"><br>
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<b><font color="#FFFFFF">Lets start!</font></b></td>
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<p>To start, we take the program from tutorial 2, which loaded and displayed
a quake 3 level. We will use the level to walk in it and to pick triangles
from it. In addition we'll place 3 animated models into it for scene
node picking. The following code starts up the engine and loads a
quake 3 level. I will not explain it, because it should already be
known from tutorial 2.</p>
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<td> <pre><font size="2"><font color="#008000">#include <irrlicht.h>
#include <iostream><br>
</font><b>using namespace </b>irr;
<font color="#008000">#pragma comment(lib, "Irrlicht.lib")
</font><b>int </b>main()
{
<font color="#008000"> // let user select driver type</font>
<br> video::E_DRIVER_TYPE driverType;<br><br> printf("Please select the driver you want for this example:\n"\<br> " (a) Direct3D 9.0c\n (b) Direct3D 8.1\n (c) OpenGL 1.5\n"\<br> " (d) Software Renderer\n (e) Apfelbaum Software Renderer\n"\<br> " (f) NullDevice\n (otherKey) exit\n\n");<br><br> char i;<br> std::cin >> i;<br><br> switch(i)<br> {<br> case 'a': driverType = video::EDT_DIRECT3D9;break;<br> case 'b': driverType = video::EDT_DIRECT3D8;break;<br> case 'c': driverType = video::EDT_OPENGL; break;<br> case 'd': driverType = video::EDT_SOFTWARE; break;<br> case 'e': driverType = video::EDT_BURNINGSVIDEO;break; <br> case 'f': driverType = video::EDT_NULL; break;<br> default: return 0;<br> } <br>
<font color="#008000"> // create device</font></font></pre>
<pre> IrrlichtDevice *device = createDevice(driverType,
core::dimension2d<s32>(640, 480), 16, false);<br>
if (device == 0)<br> return 1; // could not create selected driver.<br><br> video::IVideoDriver* driver = device->getVideoDriver();<br> scene::ISceneManager* smgr = device->getSceneManager();<br><br> <font size="2">device->getFileSystem()->addZipFileArchive<br> (<font color="#FF0000">"../../media/map-20kdm2.pk3"</font>);
scene::IAnimatedMesh* q3levelmesh = smgr->getMesh(<font color="#FF0000">"20kdm2.bsp"</font>);
scene::ISceneNode* q3node = <font color="#800080">0</font>;
<b>if </b>(q3levelmesh)
q3node = smgr->addOctTreeSceneNode(q3levelmesh->getMesh(<font color="#800080">0</font>));
</font></pre>
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<p> So far so good, we've loaded the quake 3 level like in tutorial
2. Now, here comes something different: We create a triangle selector.
A triangle selector is a class which can fetch the triangles from
scene nodes for doing different things with them, for example collision
detection. There are different triangle selectors, and all can be
created with the ISceneManager. In this example, we create an OctTreeTriangleSelector,
which optimizes the triangle output a little bit by reducing it like
an octree. This is very useful for huge meshes like quake 3 levels.<br>
Afte we created the triangle selector, we attach it to the q3node.
This is not necessary, but in this way, we do not need to care for
the selector, for example dropping it after we do not need it anymore.</p>
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<td> <pre><font size="2">scene::ITriangleSelector* selector = <font color="#800080">0</font>;
<b>if </b>(q3node)
{
q3node->setPosition(core::vector3df(-<font color="#800080">1370</font>,-<font color="#800080">130</font>,-<font color="#800080">1400</font>));
selector = smgr->createOctTreeTriangleSelector(
q3levelmesh->getMesh(<font color="#800080">0</font>), q3node, <font color="#800080">128</font>);
q3node->setTriangleSelector(selector);
}</font></pre></td>
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<p> We add a first person shooter camera to the scene for being able
to move in the quake 3 level like in tutorial 2. But this, time, we
add a special animator to the camera: A Collision Response animator.
This thing modifies the scene node to which it is attached to in that
way, that it may no more move through walls and is affected by gravity.
The only thing we have to tell the animator is how the world looks
like, how big the scene node is, how gravity and so on. After the
collision response animator is attached to the camera, we do not have
to do anything more for collision detection, anything is done automaticly,
all other collision detection code below is for picking. And please
note another cool feature: The collsion response animator can be attached
also to all other scene nodes, not only to cameras. And it can be
mixed with other scene node animators. In this way, collision detection
and response in the Irrlicht<br>
engine is really, really easy.<br>
Now we'll take a closer look on the parameters of createCollisionResponseAnimator().
The first parameter is the TriangleSelector, which specifies how the
world, against collision detection is done looks like. The second
parameter is the scene node, which is the object, which is affected
by collision detection, in our case it is the camera. The third defines
how big the object is, it is the radius of an ellipsoid. Try it out
and change the radius to smaller values, the camera will be able to
move closer to walls after this. The next parameter is the direction
and speed of gravity. You could set it to (0,0,0) to disable gravity.
And the last value is just a translation: Without this, the ellipsoid
with which collision detection is done would be around the camera,
and the camera would be in the middle of the ellipsoid. But as human
beings, we are used to have our eyes on top of the body, with which
we collide with our world, not in the middle of it. So we place the
scene node 50 units over the center of the ellipsoid with this parameter.
And that's it, collision detection works now. <br>
</p>
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<td> <pre><font size="2"> scene::ICameraSceneNode* camera = <br> camera = smgr->addCameraSceneNodeFPS(<font color="#800080">0</font>,<font color="#800080">100.0f</font>,<font color="#800080">300.0f</font>);
camera->setPosition(core::vector3df(-10<font color="#800080">0</font>,<font color="#800080">50</font>,-15<font color="#800080">0</font>));
scene::ISceneNodeAnimator* anim =<br> smgr->createCollisionResponseAnimator(
selector, camera, core::vector3df(<font color="#800080">30</font>,<font color="#800080">50</font>,<font color="#800080">30</font>),
core::vector3df(<font color="#800080">0</font>,<font color="#800080">-3</font>,<font color="#800080">0</font>),
core::vector3df(<font color="#800080">0</font>,<font color="#800080">50</font>,<font color="#800080">0</font>));<br>
selector->drop();<br>
camera->addAnimator(anim);
anim->drop();</font></pre></td>
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<p> Because collision detection is no big deal in irrlicht, I'll describe
how to do two different types of picking in the next section. But
before this, I'll prepare the scene a little. I need three animated
characters which we <br>
could pick later, a dynamic light for lighting them, a billboard for
drawing where we found an intersection, and, yes, I need to get rid
of this mouse cursor. :)</p>
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<td> <pre><font size="2"> <font color="#0A246A"><i>// disable mouse cursor
</i></font> device->getCursorControl()->setVisible(<b>false</b>);
<font color="#0A246A"><i>// add billboard
</i></font> scene::IBillboardSceneNode * bill = smgr->addBillboardSceneNode();
bill->setMaterialType(video::EMT_TRANSPARENT_ADD_COLOR );
bill->setMaterialTexture(<font color="#800080">0</font>, driver->getTexture(<br> <font color="#FF0000">"../../media/particle.bmp"</font>));
bill->setMaterialFlag(video::EMF_LIGHTING, <b>false</b>);
bill->setSize(core::dimension2d<f32>(<font color="#800080">20.0f</font>, <font color="#800080">20.0f</font>));
<font color="#0A246A"><i>// add 3 animated faeries.
</i></font> video::SMaterial material;
material.Texture1 = driver->getTexture(<font color="#FF0000"><br> "../../media/faerie2.bmp"</font>);
material.Lighting = <b>true</b>;
scene::IAnimatedMeshSceneNode* node = <font color="#800080">0</font>;
scene::IAnimatedMesh* faerie = smgr->getMesh(<br> <font color="#FF0000">"../../media/faerie.md2"</font>);
<b>if </b>(faerie)
{
node = smgr->addAnimatedMeshSceneNode(faerie);
node->setPosition(core::vector3df(-<font color="#800080">70</font>,<font color="#800080">0</font>,-<font color="#800080">90</font>));
node->setMD2Animation(scene::EMAT_RUN);
node->getMaterial(<font color="#800080">0</font>) = material;
node = smgr->addAnimatedMeshSceneNode(faerie);
node->setPosition(core::vector3df(-<font color="#800080">70</font>,<font color="#800080">0</font>,-<font color="#800080">30</font>));
node->setMD2Animation(scene::EMAT_SALUTE);
node->getMaterial(<font color="#800080">0</font>) = material;
node = smgr->addAnimatedMeshSceneNode(faerie);
node->setPosition(core::vector3df(-<font color="#800080">70</font>,<font color="#800080">0</font>,-<font color="#800080">60</font>));
node->setMD2Animation(scene::EMAT_JUMP);
node->getMaterial(<font color="#800080">0</font>) = material;
}
material.Texture1 = <font color="#800080">0</font>;
material.Lighting = <b>false</b>;
<font color="#0A246A"><i>// Add a light
</i></font> smgr->addLightSceneNode(<font color="#800080">0</font>, core::vector3df(-<font color="#800080">60</font>,<font color="#800080">100</font>,<font color="#800080">400</font>),
video::SColorf(<font color="#800080">1.0f</font>,<font color="#800080">1.0f</font>,<font color="#800080">1.0f</font>,<font color="#800080">1.0f</font>),
<font color="#800080">600.0f</font>);</font></pre></td>
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<p>For not making it to complicated, I'm doing picking inside the drawing
loop. We take two pointers for storing the current and the last selected
scene node and start the loop.</p>
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<td> <pre><font size="2"> scene::ISceneNode* selectedSceneNode = <font color="#800080">0</font>;
scene::ISceneNode* lastSelectedSceneNode = <font color="#800080">0</font>;
<b>int </b>lastFPS = -<font color="#800080">1</font>;
<b>while</b>(device->run())<br> <strong>if</strong> (device->isWindowActive())
{
driver->beginScene(<b>true</b>, <b>true</b>, <font color="#800080">0</font>);
smgr->drawAll();</font></pre></td>
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<p> After we've drawn the whole scene whit smgr->drawAll(), we'll do
the first picking: We want to know which triangle of the world we are
looking at. In addition, we want the exact point of the quake 3 level
we are looking at. For this, we create a 3d line starting at the position
of the camera and going through the lookAt-target of it. Then we ask
the collision manager if this line collides with a triangle of the world
stored in the triangle selector. If yes, we draw the 3d triangle and
set the position of the billboard to the intersection point. </p>
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<td><pre><font size="2"> core::line3d<f32> line;
line.start = camera->getPosition();
line.end = line.start +
(camera->getTarget() - line.start).normalize() * <font color="#800080">1000.0f</font>;
core::vector3df intersection;
core::triangle3df tri;
<b>if </b>(smgr->getSceneCollisionManager()->getCollisionPoint(
line, selector, intersection, tri))
{
bill->setPosition(intersection);
driver->setTransform(video::ETS_WORLD, core::matrix4());
driver->setMaterial(material);
driver->draw3DTriangle(tri, video::SColor(<font color="#800080">0</font>,<font color="#800080">255</font>,<font color="#800080">0</font>,<font color="#800080">0</font>));
}</font></pre></td>
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<p> Another type of picking supported by the Irrlicht Engine is scene
node picking based on bouding boxes. Every scene node has got a bounding
box, and because of that, it's very fast for example to get the scene
node which the camera looks<br>
at. Again, we ask the collision manager for this, and if we've got a
scene node, we highlight it by disabling Lighting in its material, if
it is not the billboard or the quake 3 level. </p>
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<td><pre><font size="2"> selectedSceneNode = smgr->getSceneCollisionManager()->
getSceneNodeFromCameraBB(camera);
<b>if </b>(lastSelectedSceneNode)
lastSelectedSceneNode->setMaterialFlag(
video::EMF_LIGHTING, <b>true</b>);
<b>if </b>(selectedSceneNode == q3node ||
selectedSceneNode == bill)
selectedSceneNode = <font color="#800080">0</font>;
<b>if </b>(selectedSceneNode)
selectedSceneNode->setMaterialFlag(
video::EMF_LIGHTING, <b>false</b>);
lastSelectedSceneNode = selectedSceneNode;</font></pre></td>
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<p> That's it, we just have to finish drawing.</p>
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<td> <pre><font size="2"> driver->endScene();
<b>int </b>fps = driver->getFPS();
<b>if </b>(lastFPS != fps)
{
core::stringw str = L"Collision detection example - Irrlicht Engine [";<br> str += driver->getName();<br> str += "] FPS:";<br> str += fps;<br><br> device->setWindowCaption(str.c_str());<br> lastFPS = fps;<br> }
}
device->drop();
<b>return </b><font color="#800080">0</font>;
}
</font></pre></td>
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<p> </p>
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