de.grogra.ray.physics
Interface Emitter

All Superinterfaces:

Scattering

All Known Subinterfaces:

Light, Light, Sensor

All Known Implementing Classes:

AmbientLight, Camera, DirectionalLight, LightBase, Parallelogram, PhysicalLight, PointLight, SensorNode, Sky, SpectralLight, SpotLight, SunSkyLight, SunSkyToDirectionalLightWrapper

public interface Emitter
extends Scattering

The Emitter interface is the superinterface for all entities which emit a quantity of light transport: Light sources emit radiance, Sensors emit importance. Both sources and sensors are located at the extremal vertices of a complete light path, this interface provides the common methods needed for Monte Carlo-based photon tracing.

Author:

Ole Kniemeyer

Field Summary

Fields inherited from interface de.grogra.ray.physics.Scattering

DELTA_FACTOR, IS_NON_OPAQUE, MIN_UNUSED_FLAG, NEEDS_NORMAL, NEEDS_POINT, NEEDS_TANGENTS, NEEDS_TRANSFORMATION, NEEDS_UV, RANDOM_RAYS_GENERATE_ORIGINS

Method Summary

double	completeRay(Environment env, Point3d vertex, Ray out)
double	computeExitance(Environment env, Spectrum exitance) Evaluates the exitance function for given input.
void	generateRandomOrigins(Environment env, RayList out, java.util.Random random) Pseudorandomly generates, for the given input, a set of origins for this emitter.

Methods inherited from interface de.grogra.ray.physics.Scattering

computeBSDF, generateRandomRays, getAverageColor, getFlags

Method Detail

completeRay

double completeRay(Environment env,
                   Point3d vertex,
                   Ray out)

computeExitance

double computeExitance(Environment env,
                       Spectrum exitance)

Evaluates the exitance function for given input. The computed value is the spectrum of the radiant exitance (emitted power per area) L⁰_j(x, ν) at the point env.point in case of light sources, or the corresponding function W⁰_j(x, ν) in case of sensors.

The returned value is the value of the probability density p_x that would be calculated by generateRandomOrigins(de.grogra.ray.physics.Environment, de.grogra.ray.util.RayList, java.util.Random) if env.point happened to be one of the randomly generated origins.

Parameters:

env - the environment for scattering

exitance - the exitance values will be placed in here

Returns:

the value of the probability density for the ray origin

generateRandomOrigins

void generateRandomOrigins(Environment env,
                           RayList out,
                           java.util.Random random)

Pseudorandomly generates, for the given input, a set of origins for this emitter. They are generated such that they can be used for Monte Carlo-based photon tracing algorithms in the following way.

At first, we consider the case where the emitter is in fact a light source. Let L(x, ω, ν) be the emitted spectral radiance for the frequency ν at the light's surface point x in direction ω. The radiant exitance (emitted spectral power per area) at x is defined as

L⁰(x, ν) = ∫ cos θ L(x, ω, ν) dω where θ is the angle between the surface normal and ω. Now the directional distribution of the emitted radiance at x can be described by the density L¹(x, ω, ν) = L(x, ω, ν) / L⁰(x, ν) so that the radiance is split into L(x, ω, ν) = L⁰(x, ν) L¹(x, ω, ν) Let o_i and s_i denote the origins and spectra of the N generated rays (N = rays.size). Then for a function f(x, ν) which is to be integrated over the light surface, the sum 1 / N ∑_i s_i(ν) f(o_i, ν) is an unbiased estimate for the integral ∫ L⁰(x, ν) f(x, ν) dA The integral ranges over the whole surface A of the light source. As a consequence, the spectrum of a ray is to be considered as the ray's radiant spectral power.

Now if the emitter is a sensor, let W(x, ω, ν) be the emitted spectral importance for frequency ν at the sensors's surface point x in direction ω. The quantities W⁰(x, ν) and W¹(x, ω, ν) are defined similarly to the case of light sources:

W⁰(x, ν) = ∫ cos θ W(x, ω, ν) dω
W(x, ω, ν) = W⁰(x) W¹(x, ω, ν) The formulas for light sources are valid for sensors if the L-quantites are replaced by the corresponding W-quantities.

Let p_x be the probability density used for the ray origin, then the field originDensity is set to p_x(o_i) for each ray. For emitters which are concentrated at a single point (e.g., point lights) p_x is not a regular function, the value originDensity will be set to a multiple of Scattering.DELTA_FACTOR.

The ray properties which are not mentioned in the given formulas are neither used nor modified. These are the direction and its density.

Parameters:

env - the environment

out - the outgoing rays to be generated

random - pseudorandom generator