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<p class="header" align="center">OGRE (Object-Oriented Graphics
Rendering Engine)</p>
<p class="header" align="center">Avionic Flying Lights </p>
<p class="MainHeader" align="left"> </p>
<p class="SectionHeader" align="left">Some new classes to play with</p>
<p align="left">We are now going to give the ship some lights on it's
wings and tail so that pilots of other ships can see it againt the
blackness of space. By using different colours and patterns on each of
the wings and tail, another pilot will also be able to determine which
direction the ship is facing. </p>
<p>To do this we will be using three object classes: Light,
BillboardSet, and Billboard. </p>
<p class="SectionHeader" align="left">Billboards and Materials</p>
<p align="left">A billboard simply displays a 2D image in the 3D world
that we create. Whenever a billboard is rendered it faces the viewer.
This is perfect for the lights we are about to make, they can appear as
small balls of light. The image displayed on the billboard is a
material just like any other so it needs to be defined in our material
script file. </p>
<p>Open ogrenew\Samples\Media\example.material and add the following to
the script: </p>
<pre>// Light effects<br>Examples/FlyingLightMaterial<br>{<br> lighting off<br> scene_blend add<br> depth_write off<br> {<br> texture flare.png<br> }<br> <br>}<br></pre>
It may look familiar to some of you. It is in fact the material used
for the flare effects earlier in the script, but its name has been
changed to suit our purposes.
<p></p>
<p class="SectionHeader" align="left">BillboardSets and Billboards</p>
<p align="left">A BillboardSet is a grouping of Billboards in 3D space.
The relationship between BillboardSet and Billboard is well documented
in the Ogre API so there is really no need to describe it here. </p>
<p class="SectionHeader" align="left">Member Variables</p>
<p align="left">Time to add member variables for the lights and
billboards. Add this to the protected section of our SpaceApplication
class </p>
<pre> // The set of all the billboards used for the avionic lights<br> BillboardSet* mLights;<br><br> // Billboards<br> Billboard* mRedLightBoard;<br> Billboard* mBlueLightBoard;<br> Billboard* mWhiteLightBoard;<br><br> // Lights<br> Light* mRedLight;<br> Light* mBlueLight;<br> Light* mWhiteLight;<br></pre>
<p></p>
<p class="SectionHeader" align="left">Lighting Instances</p>
<p align="left">The general flow of this is:
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<td>1) Create BillboardSet</td>
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<td>2) Set its material and attach it to the scene</td>
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<td>3) Using the new BillboardSet create as many billboards as
you require, position each of them</td>
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<td>4) Create the lights and attach them to the scene</td>
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<p align="left">So let's begin by creating the BillboardSet. Type this
in at the bottom of the createScene method </p>
<pre> // First create the BillboardSet. This will define the materials for the billboards<br> // in its set to use<br> mLights = mSceneMgr->createBillboardSet("FlyingLights");<br> mLights->setMaterialName("Examples/FlyingLightMaterial");<br> mShipNode->attachObject(mLights);<br><br></pre>
There should not be too much there that needs explaining. Like other
objects in Ogre, BillboardSets all have unique names. This one is
called "FlyingLights" and the material that we want it to be using for
its Billboards is "Examples/FlyingLightMaterial", which is of course
the material we put into the material script earlier.
<p></p>
<p></p>
Each of the three coloured lights has two properties of any interest.
Position and colour.
<pre> // Red light billboard, in "off" state<br> Vector3 redLightPosition(78, -8, -70);<br> mRedLightBoard = mLights->createBillboard(redLightPosition);<br> mRedLightBoard->setColour(ColourValue::Black);<br><br><br> // Blue light billboard, in "off" state<br> Vector3 blueLightPosition(-90, -8, -70);<br> mBlueLightBoard = mLights->createBillboard(blueLightPosition);<br> mBlueLightBoard->setColour(ColourValue::Black);<br><br><br> // White light billboard, in "off" state<br> Vector3 whiteLightPosition(-4.5, 30, -80);<br> mWhiteLightBoard = mLights->createBillboard(whiteLightPosition);<br> mWhiteLightBoard->setColour(ColourValue::Black);<br></pre>
You might notice that the positions chosen here are not symmetrical. I
originally used symmetrical values but then discovered that the lights
just would not line up on the ship. Instead of modifying the model and
distributing that I decided to just change these positions. If you find
that the lights still do not line up on your model you may want to
adjust these values yourself later on.
<p></p>
<p>The light objects are next on the list. Each of them has a distinct
name, a type, a colour, and a position. </p>
<pre> // Red light, in "off" state<br> mRedLight = mSceneMgr->createLight("RedFlyingLight");<br> mRedLight->setType(Light::LT_POINT);<br> mRedLight->setPosition(redLightPosition);<br> mRedLight->setDiffuseColour(ColourValue::Black);<br> mShipNode->attachLight(mRedLight);<br><br> // Blue light, in "off" state<br> mBlueLight = mSceneMgr->createLight("BlueFlyingLight");<br> mBlueLight->setType(Light::LT_POINT);<br> mBlueLight->setPosition(blueLightPosition);<br> mBlueLight->setDiffuseColour(ColourValue::Black);<br> mShipNode->attachLight(mBlueLight);<br><br> // White light in "off" state<br> mWhiteLight = mSceneMgr->createLight("WhiteFlyingLight");<br> mWhiteLight->setType(Light::LT_POINT);<br> mWhiteLight->setPosition(whiteLightPosition);<br> mWhiteLight->setDiffuseColour(ColourValue::Black);<br> mShipNode->attachLight(mWhiteLight);<br><br></pre>
If you run the program as it stands right now you wont notice anything
different. Why is that? well that is because we told the lights and
billboards to be black. Just to see where the lights and billboards are
try changing the colour of all of the billboards to their "on" colour.
For instance, set the colour of mRedLightBoard to ColourValue::Red.
When you run it you will then see three coloured balls, one on the left
wingtip, one on the right wingtip, and one on the tail wingtip. Change
them all back to black and save.
<p></p>
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