Module raytracer
Package de.grogra.ray.physics

Interface Scattering

All Known Subinterfaces:
Emitter, Light, Light, Scattering, Sensor, Shader, Shader
All Known Implementing Classes:
AlgorithmSwitchShader, AmbientLight, Camera, DirectionalLight, IORShader, LightBase, Material, MaterialRef, Parallelogram, Phong, PhysicalLight, PointLight, RGBAShader, SensorNode, ShaderRef, SideSwitchShader, Sky, SpectralLight, SpotLight, SunSkyLight, SunSkyToDirectionalLightWrapper, SwitchShader
public interface Scattering
A Scattering instance represents a scattering entity: Either a surface Shader, a Light source, or a Sensor. Methods are provided that a Monte Carlo-based raytracer needs for lighting calculations. This allows for any desired bidirectional scattering distribution functions (BSDF) in implementations of Scattering.
Author:
Ole Kniemeyer

  • Field Details

  • Method Details

    • getFlags

      int getFlags()

    • getAverageColor

      int getAverageColor()
      Returns an average color for the scattering entity. This color is used for simplified graphical representations of the corresponding objects.
      Returns:
      an average color in Java's default sRGB color space, encoded as an int (0xAARRGGBB).

    • generateRandomRays

      void generateRandomRays(Environment env, Vector3f out, Spectrum specOut, RayList rays, boolean adjoint, Random random)
      Pseudorandomly generates, for the given input, a set of scattered rays. The scattered rays are generated such that they can be used for a Monte Carlo integration of a function f(ω;ν) over cos θ BSDF(ωi, νi; ωo, νo) in the following way:
      • If adjoint is false, out = ωo describes the direction of an outgoing light ray. In this case, the integration is with respect to ωi. Let g(ω, ν; out, μ) = BSDF(ω, ν; out, μ)
      • Otherwise, adjoint is true. In this case, out = ωi describes the direction of an outgoing importance ray (an inverse light ray). Now the integration is with respect to ωo. Let g(ω, ν; out, μ) = BSDF(out, μ; ω, ν)
      Let di and si denote the directions and spectra of the N generated rays (N = rays.size). Then, for every frequency ν the sum
      1 / N ∑i si(ν) f(di; ν)
      is an unbiased estimate for the integral
      ∫ cos θ f(ω; ν) g(ω, ν; out, μ) specOut(μ) dμ dω
      θ is the angle between the surface normal and ω. The domain of integration is the whole sphere, since the bidirectional scattering distribution includes both reflection and transmission (BSDF = BRDF + BTDF).

      If this Scattering instance is in fact a Light source, adjoint is true, and the BSDF is defined as BSDF(out, μ; ω, ν) = L1(ω, ν) δ(μ - ν), i.e., the directional distribution of the emitted radiance at env.point, see Emitter. In this case, out is not used.

      If this Scattering instance is in fact a Sensor, adjoint is false, and the BSDF is defined as BSDF(ω, ν; out, μ) = W1(ω, ν) δ(μ - ν), i.e., the directional distribution of the emitted importance at env.point, see Emitter. In this case, out is not used.

      Let pω be the probability density used for the ray direction (measured with respect to solid angle ω), then the field directionDensity of the ray i is set to pω(di). For ideal specular reflection or transmission, or for directional lights or sensors, pω is not a regular function, the value directionDensity will be set to a multiple of DELTA_FACTOR.

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

      Parameters:
      env - the environment for scattering
      out - the direction unit vector of the outgoing ray (i.e., pointing away from the surface)
      specOut - the spectrum of the outgoing ray
      rays - the rays to be generated
      adjoint - represents out a light ray or an importance ray?
      random - pseudorandom generator
      See Also:

    • computeBSDF

      float computeBSDF(Environment env, Vector3f in, Spectrum specIn, Vector3f out, boolean adjoint, Spectrum bsdf)
      Evaluates bidirectional scattering distribution function for given input.

      The computed spectrum is an integral over the spectrum of the following product:

      |cos θ| BSDF(ωi, νi; ωo, νo)
      where BSDF is the bidirectional scattering distribution function (= BRDF + BTDF) at the point env.point, ωi the (negated) direction of the incoming light ray, νi the frequency where the incoming ray is sampled, ωo the direction of the outgoing light ray, νo the frequency where the outgoing ray is sampled, and θ the angle between the surface normal and out.

      If adjoint is false, in and out describe true light rays from light sources to sensors. In this case, ωi = in, ωo = out, and the integral is

      bsdf(ν) = |cos θ| ∫ BSDF(in, νi; out, ν) specIn(νi) dνi
      Otherwise, adjoint is true. in and out then describe importance rays (inverse light rays from sensors to light sources). In this case, ωi = out, ωo = in, and the integral is
      bsdf(ν) = |cos θ| ∫ BSDF(out, ν; in, νo) specIn(νo) dνo

      If this Scattering instance is in fact a Light source, adjoint is false, and the BSDF is defined as BSDF(in, μ; ω, ν) = L1(ω, ν) δ(μ - ν), i.e., the directional distribution of the emitted radiance at env.point, see Emitter. In this case, in is not used.

      If this Scattering instance is in fact a Sensor, adjoint is true, and the BSDF is defined as BSDF(ω, ν; in, μ) = W1(ω, ν) δ(μ - ν), i.e., the directional distribution of the emitted importance at env.point, see Emitter. In this case, in is not used.

      The computation should be physically valid. This excludes, e.g., ambient or emissive light contributions.

      The returned value is the value of the probability density pω that would be calculated by generateRandomRays(de.grogra.ray.physics.Environment, javax.vecmath.Vector3f, de.grogra.ray.physics.Spectrum, de.grogra.ray.util.RayList, boolean, java.util.Random) if the ray happened to be one of the randomly generated rays.

      Parameters:
      env - the environment for scattering
      in - the (negated) direction unit vector of the incoming ray (i.e., pointing away from the surface)
      specIn - the spectrum of the incoming ray
      out - the direction unit vector of the outgoing ray (i.e., pointing away from the surface)
      adjoint - light ray or importance ray?
      bsdf - the computed spectrum of the outgoing ray will be placed in here
      Returns:
      the value of the probability density for the ray direction