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<p class="header" align="center">OGRE (Object-Oriented Graphics
Rendering Engine)</p>
<p class="header" align="center">Using Waveform Controllers </p>
<p class="MainHeader" align="left"> </p>
<p class="SectionHeader" align="left">Controllers, ControllerFunctions,
and ControllerValues</p>
<p align="left">When I initially wrote the source for the tutorial I
used two variables of type Real, and two booleans for each light to
control its flashing. The code was a couple pages long and it would
have been very hard to extend the functionality of it. I thought to
myself that it would be nice if I could just set up the logic of
controlling the colour value of a Light and Billboard pair just once
and let different time based functions control the intensity. Just when
I was about to make my own I discovered that Ogre has these built into
it. And now they are my new best friends. </p>
<p>The way it hangs together in Ogre is that you create a class
descending from ControllerValue which overrides the methods getValue
and setValue. The names should make their function obvious enough but
one thing to note is that they only deal with values between 0.0 and
1.0. </p>
<p>A ControllerFunction is given a value to operate on and outputs a
result between 0.0 and 1.0, which gets fed to a ControllerValue. These
functions can be based on anything, but for this tutorial we will only
focus on using it to control values based on time. </p>
<p>A Controller connects a ControllerFunction with an input
ControllerValue and an output ControllerValue. The most useful input
ControllerValue to us comes from a method on the ControllerManager
called getFrameTimeSource which will give the value of time between
frames. </p>
<p class="SectionHeader" align="left">Controllers, ControllerFunctions,
and ControllerValues</p>
<p align="left">With our new found knowledge of controllers lets make a
ControllerValue and ControllerFunction to control these lights. Go to
the top of the Space.h file just after #include "ExampleApplication.h
and enter this </p>
<pre>class LightFlasher : public ControllerValue<Real><br>{<br>protected:<br> Light* mLight;<br> Billboard* mBillboard;<br> ColourValue mMaxColour;<br> Real intensity;<br>public:<br> LightFlasher(Light* light, Billboard* billboard, ColourValue maxColour)<br> {<br> mLight = light;<br> mBillboard = billboard;<br> mMaxColour = maxColour;<br> }<br><br> virtual Real getValue (void) const<br> {<br> return intensity;<br> }<br><br> virtual void setValue (Real value)<br> {<br> intensity = value;<br><br> ColourValue newColour;<br><br> // Attenuate the brightness of the light<br> newColour.r = mMaxColour.r * intensity;<br> newColour.g = mMaxColour.g * intensity;<br> newColour.b = mMaxColour.b * intensity;<br><br> mLight->setDiffuseColour(newColour);<br> mBillboard->setColour(newColour);<br> }<br>};<br></pre>
<p align="left">When the controller calls setValue, the value is used
to attentuate the Red, Green, and Blue values of the Light and
Billboard. The effect of this will be that when the value is set to 0.0
the light will be black which is the same as being off, and when set to
1.0 the light will be at its brightest. </p>
<p></p>
<p align="left">The ControllerFunction that we will use will be based
on WaveformControllerFunction. We do not need to modify the class very
much, in fact all we will do is override the constructor and default
some of the arguments to make using it a little easier. </p>
<pre>class LightFlasherControllerFunction : public WaveformControllerFunction<br>{<br>public:<br> LightFlasherControllerFunction(WaveformType wavetype, Real frequency, Real phase) : WaveformControllerFunction(wavetype, 0, frequency, phase, 1, true)<br> {<br><br> }<br>};<br></pre>
The constructor for a WaveformControllerFunction is
<pre>WaveformControllerFunction::WaveformControllerFunction(WaveformType wType, Real base, Real frequency, Real phase, Real amplitude, bool delta)<br></pre>
The first argument, WaveformType is the type of wave to be generated,
which can be a sine, traingle, square, sawtooth, or inverse sawtooth.
We will use most of these wave forms in the tutorial. Base is added to
the value generated, it effectively sets the bottom value of the wave
and we will only use 0.0 in this tutorial so it has been hardcoded in
the constructor. Frequency is how often the whole wave form is produced
within one second. Phase is how far through the wave to start in.
Amplitude is multiplied to the wave value to increase the size of the
wave, we will only use 1.0 for this. Delta is used internally to
specify wether or not the values are supplied as delta or absolute
values, defaulting here to true.
<p></p>
<p class="SectionHeader" align="left">Switching the lights on</p>
<p align="left">In the previous tutorial we had to turn the ambient
lighting on so that we could see the ship but now we want to turn it
back down again so that we can see the effects of our new light
sources. So in the createScene method change the line setting the
ambient lighting to </p>
<pre> // Set a very low level of ambient lighting<br> mSceneMgr->setAmbientLight(ColourValue(0.2, 0.2, 0.2));<br></pre>
We need some member variables to hold the Controllers and their Values
and Functions. Add these to the protected section of the class.
<pre> // Light flashers<br> LightFlasher* mRedLightFlasher;<br> LightFlasher* mBlueLightFlasher;<br> LightFlasher* mWhiteLightFlasher;<br><br> // Light controller functions<br> LightFlasherControllerFunction* mRedLightControllerFunc;<br> LightFlasherControllerFunction* mBlueLightControllerFunc;<br> LightFlasherControllerFunction* mWhiteLightControllerFunc;<br><br> // Light controllers<br> Controller* mRedLightController;<br> Controller* mBlueLightController;<br> Controller* mWhiteLightController;<br><br></pre>
And now, finally, we create our controllers. Type this into the bottom
of the createScene method.
<pre> // Light flashers<br> mRedLightFlasher = new LightFlasher(mRedLight, mRedLightBoard, ColourValue::Red);<br> mBlueLightFlasher = new LightFlasher(mBlueLight, mBlueLightBoard, ColourValue::Blue);<br> mWhiteLightFlasher = new LightFlasher(mWhiteLight, mWhiteLightBoard, ColourValue::White);<br><br> // Light controller functions<br> mRedLightControllerFunc = new LightFlasherControllerFunction(Ogre::WFT_SINE, 0.5, 0.0);<br> mBlueLightControllerFunc = new LightFlasherControllerFunction(Ogre::WFT_SQUARE, 0.5, 0.5);<br> mWhiteLightControllerFunc = new LightFlasherControllerFunction(Ogre::WFT_TRIANGLE, 4, 0.0);<br><br> // Light controllers<br> ControllerManager* mControllerManager = &ControllerManager::getSingleton();<br> mRedLightController = mControllerManager->createController(mControllerManager->getFrameTimeSource(), mRedLightFlasher, mRedLightControllerFunc);<br> mBlueLightController = mControllerManager->createController(mControllerManager->getFrameTimeSource(), mBlueLightFlasher, mBlueLightControllerFunc);<br> mWhiteLightController = mControllerManager->createController(mControllerManager->getFrameTimeSource(), mWhiteLightFlasher, mWhiteLightControllerFunc);<br><br><br></pre>
There is one LightFlasher for each of Red, Blue, and White connected to
their respective Light and Billboard. Then we create one
ControllerFunction to pulse the red light in a sine wave fashion, one
to flash the blue light on and off, and one to pulse the white light 4
times a second in a triangle wave fashion. We then use the
ControllerManager to create three Controllers, one for each light and
hook them up to their ControllerFunctions and ControllerValues. The
first argument to their constructors is a call to getFrameTimeSource,
which will give us an object that provides the Controller with time
information.
<p></p>
<p>Compile and run the program. The lights should be flashing or
pulsing as described above. </p>
<p class="SectionHeader" align="left">Blinking Lights</p>
<p align="left">I said earlier that is is easier to extend the
functionality of this than my first attempt. Lets do it now by changing
the way that the white light works. Lets make it blink on for one tenth
of a second once every 4 seconds. To do this we will create a new class
called LightBlinker inheriting from the LightFlasher. It will be
designed to accept input from the sawtooth wave and when the wave hits
a certain value we will turn the light on, otherwise the light will
remain off. </p>
<p>Put this class definition just after the definition of LightFlasher.
</p>
<pre>class LightBlinker : public LightFlasher<br>{<br>protected:<br> ColourValue mMinColour;<br> Real mActivationLevel;<br>public:<br> LightBlinker(Light* light, Billboard* billboard, ColourValue maxColour, ColourValue minColour, Real activationLevel) : LightFlasher(light, billboard, maxColour)<br> {<br> mMinColour = minColour;<br> mActivationLevel = activationLevel;<br> }<br><br> virtual Real getValue (void) const<br> {<br> return intensity;<br> }<br><br> virtual void setValue(Real value)<br> {<br> intensity = value;<br><br><br> if(value < mActivationLevel)<br> {<br> // Light is off<br> mLight->setDiffuseColour(mMinColour);<br> mBillboard->setColour(mMinColour);<br> } else {<br> // Light is blinking on<br> mLight->setDiffuseColour(mMaxColour);<br> mBillboard->setColour(mMaxColour);<br> }<br> }<br><br>};<br><br></pre>
Lets now use our new class. Change the line creating the light
controller function for the white light to be
<pre> mWhiteLightControllerFunc = new LightFlasherControllerFunction(Ogre::WFT_SAWTOOTH, 0.25, 0.0);<br></pre>
And the line creating the white light flasher.
<pre> mWhiteLightFlasher = new LightBlinker(mWhiteLight, mWhiteLightBoard, ColourValue::White, ColourValue::Black, 0.975);<br></pre>
So what is this value of 0.975? As described above it is the value that
the wave must reach before the light will turn on. But why that
particular value? This is the way it works: the saw tooth wave starts
at 0 and hits 1.0 at the end of 4 seconds (frequency is 0.25 as stated
in the constructor for the LightFlasherFunction). This means that each
second will contribute 0.25 to the value. We however only want one
tenth of a second, leaving us with 0.025 and since we want the light to
be on for only that last tenth of a second we subtract 0.025 from 1.0
and we get 0.975, clear enough?
<p></p>
<p>Compile and run the program so far. You should have all three lights
working but the white light will blink on only once every 4 seconds. </p>
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