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In this tutorial we will see how to get started with a FluxModel in GroIMP.

Go [[01_user_documentation:08_light:02_gpu|here]] to see more about how the FluxModel is defined in GroIMP.

====== Light Model ======

First, we setup of the Flux Light Model:

<code java>
import de.grogra.gpuflux.tracer.FluxLightModelTracer.MeasureMode;
import de.grogra.gpuflux.scene.experiment.Measurement;

const int RAYS = 10000000;
const int DEPTH = 10;
const FluxLightModel LM = new FluxLightModel(RAYS,
DEPTH);

protected void init () {
LM.setMeasureMode(MeasureMode.FULL_SPECTRUM);
LM.setSpectralBuckets(81);
LM.setSpectralDomain(380, 780);
}
</code>

This is:
  - importing of the needed classes
  - initializing the model with 10 million rays and a recursion depth of 10
  - setting the parameters with 400nm divided into 80 buckets of 5nm.

Then, run the light model and determine the amount of sensed radiation or of
absorbed power for an object-type.

<code java>
public void run () [
{
LM.compute();
}


x:SensorNode ::> {
Measurement spectrum = LM.getSensedIrradianceMeasurement(x);
float absorbedPower = spectrum.integrate();
//...
} 

x:Box ::> {
Measurement spectrum = LM.getAbsorbedPowerMeasurement(x);
float absorbedPower = spectrum.integrate();
//...
}
]
</code>

This is:
  - computing the model
  - computing the integration of the whole absorbed spectrum for both
  - sensor nodes
  - box objects

Demonstration of the method for the determination of the amount of absorbed power per bucket or integration over a certain spectral range.

<code java>
Measurement spectrum = LM.getAbsorbedPowerMeasurement(x); 

//absorbed power for the first bucket: 380-385 nm
float ap380_385 = spectrum.data[0]; 

//accumulate absorbed power for the first four 50 nm buckets
float b0 = 0, b1 = 0, b2 = 0, b3 = 0;
for (int i:(0:10)) {
b0 += spectrum.data[i];
b1 += spectrum.data[i + 10];
b2 += spectrum.data[i + 20];
b3 += spectrum.data[i + 30];
} 

//integrate the whole spectrum
float ap = spectrum.integrate();
</code>

This is:
  - Getting the absorbed spectrum
  - Storing the first bucket in a variable
  - building four integrals, each of 50 nm (10 buckets of 5 nm) and sum up the first 40 buckets.
  - calculating the integral over the whole spectrum.


====== Light Sources ====== 

Now let's set up a parameterisable light node – with explicit definition of physical light and spectral power distribution by simple arrays:

<code java>
import de.grogra.imp3d.spectral.IrregularSpectralCurve; 

const double[][] DISTRIBUTION = {
{131.25, 131.67, 132.37, ...},
{131.36, 131.81, ...},
...
};

static const float[] WAVELENGTHS = {380,385, ...};
static const float[] AMPLITUDES = {0.000967,0.000980, ...};

module MyLamp extends LightNode() {
{
setLight(new SpectralLight(
new IrregularSpectralCurve(WAVELENGTHS, AMPLITUDES)).(
setPower(10), //[W]
setLight(new PhysicalLight(DISTRIBUTION))));
}
}
</code>

This is :
  - importing the required classes
  - defining of the physical light distribution
  - defining of the spectral power distribution
  - defining of a lamp using the specified parameters

The light distribution and spectral distribution (i.e. the ''DISTRIBUTION'', ''WAVELENGTHS'' and ''AMPLITUDES'' arrays) can also be provided from ''.ies'' files. 

See [[01_user_documentation:03_interacting_with_groimp:14_io:99_all_mimetypes|here]] for more information on the supported file formats.

Then, let's create a parameterizable light node – using file references for physical and spectral power distribution.

<code java>
const LightDistributionRef DISTRIBUTION = light("
distribution1");
const SpectrumRef SPECTRUM = spectrum("equal");

module MyLamp1 extends LightNode {
{
setLight(new SpectralLight(new PhysicalLight(
DISTRIBUTION), SPECTRUM, 10)); // 10 W
}
}

module MyLamp2 extends LightNode {
{
setLight(
new SpectralLight().(
setPower(10), //[W]
setLight(new PhysicalLight(DISTRIBUTION)),
setSpectrum(SPECTRUM)));
}
}
</code>

This is: 
  - Defining a file reference. This file can be included or linked to a project
  - Applying a concrete lamp to the reference by:
    - using the constructor
    - using the set-methods of the //LightNode// class


====== Illumination Model ======

Definition of a Phong shader by textures, by colours and by a user-defined
spectral power distribution.

<code java>
Phong myShader = new Phong();
ImageMap image = new ImageMap();
image.setImageAdapter(new FixedImageAdapter(image("leaf").toImageAdapter().getBufferedImage()));
myShader.setDiffuse(image);

Phong myShader = new Phong();
myShader.setDiffuse(new RGBColor(0,1,0));
//myShader.setSpecular(new Graytone(0.5));
//myShader.setShininess(new Graytone(0.5));
myShader.setDiffuseTransparency(new RGBColor(0.5,0,0));
//myShader.setAmbient(new Graytone(0.5));
//myShader.setEmissive(new Graytone(0.5));

ChannelSPD MySPD = new ChannelSPD(new IrregularSpectralCurve(
    new float[] {400,410, ....,740,750}, //WAVELENGTHS
    new float[] {0.1,0, .... ,0.4,0.25} //AMPLITUDES
));
Phong myShader = new Phong();
myShader.setDiffuse(MySPD);
</code>

This is:
  - Setting an image as texture: Values for reflection depend on the colour of the texture at each pixel of the image. 
  - Setting specific properties: At this configuration green will be reflected to 100 % and red will be transmitted to 50 % for the whole surface of the object.
  - A user-defined SPD is used to define the diffuse colour.