de.grogra.imp3d.shading
Class SwitchShader

java.lang.Object
  de.grogra.persistence.ShareableBase
      de.grogra.imp3d.shading.SwitchShader

All Implemented Interfaces:

Manageable, Shareable, Scattering, Shader

Direct Known Subclasses:

AlgorithmSwitchShader, SideSwitchShader

public abstract class SwitchShader
extends ShareableBase
implements Shader

This abstract base class defines a shader which switches between a set of actual shaders based on the shading environment and ray direction. This can be used, e.g., to use different shaders for front and back side (see the subclass SideSwitchShader), or to use different shaders depending on the algorithm (raytracer or light model).

Author:

Ole Kniemeyer

Nested Class Summary

static class

SwitchShader.Type

Field Summary

static SwitchShader.Type

$TYPE

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

LAMBERTIAN_VARIANCE

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

Constructor Summary

SwitchShader()

Method Summary

float	computeBSDF(Environment env, Vector3f in, Spectrum specIn, Vector3f out, boolean adjoint, Spectrum bsdf) Evaluates bidirectional scattering distribution function for given input.
void	computeMaxRays(Environment env, Vector3f in, Spectrum specIn, Ray reflected, Tuple3f refVariance, Ray transmitted, Tuple3f transVariance) Computes, for the given input, the reflected and transmitted importance rays for which the reflection/transmission probability densities (integrated over the spectrum) attain a maximum.
void	generateRandomRays(Environment env, Vector3f out, Spectrum specOut, RayList rays, boolean adjoint, java.util.Random rnd) Pseudorandomly generates, for the given input, a set of scattered rays.
protected abstract Shader	getShaderFor(Environment env, Vector3f in) This method has to be implemented by subclasses and defines the actual shader which shall be used depending on the environment and the ray direction.
boolean	isTransparent()
void	shade(Environment env, RayList in, Vector3f out, Spectrum specOut, Tuple3d color) Computes color of outgoing light ray for given input.
protected void	transformEnvironment(Environment e)

Methods inherited from class de.grogra.persistence.ShareableBase

addReference, appendReferencesTo, fieldModified, getProvider, getStamp, initProvider, manageableReadResolve, manageableWriteReplace, removeReference

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface de.grogra.imp3d.shading.Shader

accept

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

getAverageColor, getFlags

Methods inherited from interface de.grogra.persistence.Manageable

getManageableType

Field Detail

$TYPE

public static final SwitchShader.Type $TYPE

Constructor Detail

SwitchShader

public SwitchShader()

Method Detail

computeBSDF

public float computeBSDF(Environment env,
                         Vector3f in,
                         Spectrum specIn,
                         Vector3f out,
                         boolean adjoint,
                         Spectrum bsdf)

Description copied from interface: Scattering

Evaluates bidirectional scattering distribution function for given input.

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

|cos θ| BSDF(ω_i, ν_i; ω_o, ν_o) where BSDF is the bidirectional scattering distribution function (= BRDF + BTDF) at the point env.point, ω_i the (negated) direction of the incoming light ray, ν_i the frequency where the incoming ray is sampled, ω_o the direction of the outgoing light ray, ν_o 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, ω_i = in, ω_o = out, and the integral is

bsdf(ν) = |cos θ| ∫ BSDF(in, ν_i; out, ν) specIn(ν_i) dν_i Otherwise, adjoint is true. in and out then describe importance rays (inverse light rays from sensors to light sources). In this case, ω_i = out, ω_o = in, and the integral is bsdf(ν) = |cos θ| ∫ BSDF(out, ν; in, ν_o) specIn(ν_o) dν_o

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 p_ω that would be calculated by Scattering.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.

Specified by:

computeBSDF in interface Scattering

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

computeMaxRays

public void computeMaxRays(Environment env,
                           Vector3f in,
                           Spectrum specIn,
                           Ray reflected,
                           Tuple3f refVariance,
                           Ray transmitted,
                           Tuple3f transVariance)

Description copied from interface: Shader

Computes, for the given input, the reflected and transmitted importance rays for which the reflection/transmission probability densities (integrated over the spectrum) attain a maximum. The reflection probability density (measured with respect to solid angle) for the outgoing importance direction (i.e., incoming light direction) ω, given a fixed incident direction in, is p_r(ω) = cos θ BRDF(ω, in) / R where BRDF is the bidirectional reflectivity distribution function, θ the angle between the surface normal and ω, and R the total reflectivity for the incident direction, i.e., the integral over cos θ BRDF(ω, in). The transmission probability density is defined correspondingly.

The color-fields are set to the total reflectivity/transparency for the incident direction for each color component R, G, B. Thus, for physically plausible BRDF/BTDF, the component-wise sum of reflected.color and transmitted.color lies in the interval [0, 1], and the difference to 1 is the amount absorbed.

The color may be zero if there is no reflected or transmitted ray, respectively, i.e., if the surface is fully transparent, opaque, or absorbing. The origin-fields of the rays will never be set.

The computed variances are defined to be, for each color component, (approximations for) the angular mean quadratic deviations of the densities from the returned maximal ray directions. E.g., for perfect reflection/transmission, these variances are zero, whereas for a perfect lambertian reflector, the variance of reflection is ∫ cos θ (1 / π) θ² dω = (π² - 4) / 8. This is the value of Shader.LAMBERTIAN_VARIANCE.

The ray properties which are not mentioned are neither used nor modified. These are the origin and its density, and the direction density.

Specified by:

computeMaxRays in interface Shader

Parameters:

env - the environment for scattering

in - the (negated) direction unit vector of the incoming ray (i.e., pointing away from the surface)

specIn - spectrum of incoming ray

reflected - the reflected ray with maximal probability

refVariance - the angular mean quadratic deviation from reflected

transmitted - the transmitted ray with maximal probability

transVariance - the angular mean quadratic deviation from transmitted

generateRandomRays

public void generateRandomRays(Environment env,
                               Vector3f out,
                               Spectrum specOut,
                               RayList rays,
                               boolean adjoint,
                               java.util.Random rnd)

Description copied from interface: Scattering

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(ω_i, ν_i; ω_o, ν_o) in the following way:

• If adjoint is false, out = ω_o describes the direction of an outgoing light ray. In this case, the integration is with respect to ω_i. Let g(ω, ν; out, μ) = BSDF(ω, ν; out, μ)
• Otherwise, adjoint is true. In this case, out = ω_i describes the direction of an outgoing importance ray (an inverse light ray). Now the integration is with respect to ω_o. Let g(ω, ν; out, μ) = BSDF(out, μ; ω, ν)

Let d_i and s_i denote the directions and spectra of the N generated rays (N = rays.size). Then, for every frequency ν the sum 1 / N ∑_i s_i(ν) f(d_i; 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 p_ω 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 p_ω(d_i). For ideal specular reflection or transmission, or for directional lights or sensors, p_ω is not a regular function, the value directionDensity 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 origin and its density.

Specified by:

generateRandomRays in interface Scattering

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?

rnd - pseudorandom generator

See Also:

Scattering.computeBSDF(de.grogra.ray.physics.Environment, javax.vecmath.Vector3f, de.grogra.ray.physics.Spectrum, javax.vecmath.Vector3f, boolean, de.grogra.ray.physics.Spectrum)

getShaderFor

protected abstract Shader getShaderFor(Environment env,
                                       Vector3f in)

This method has to be implemented by subclasses and defines the actual shader which shall be used depending on the environment and the ray direction.

Parameters:

env - environment for which shading computations are to be performed

in - given ray direction

Returns:

actual shader to use for shading computations

isTransparent

public boolean isTransparent()

Specified by:

isTransparent in interface Shader

shade

public void shade(Environment env,
                  RayList in,
                  Vector3f out,
                  Spectrum specOut,
                  Tuple3d color)

Description copied from interface: Shader

Computes color of outgoing light ray for given input. The computed value is, for each color component j = R, G, B, the following sum over all incident rays k: ∑_k |cos θ_k| BSDF_j(ω_k, out) c_k,j where BSDF_j is the bidirectional scattering distribution function (= BRDF + BTDF) at the point env.point, ω_k and c_k the direction and color of ray k, and θ_k the angle between the surface normal and ω_k.

The computation may include physically invalid contributions, which may not fit into the formula above, e.g., ambient or emissive light contributions.

Specified by:

shade in interface Shader

Parameters:

env - the environment for scattering

in - the incoming rays

out - the direction unit vector of the outgoing ray (i.e., pointing away from the surface)

specOut - spectrum of outgoing ray

color - the output color will be placed in here

transformEnvironment

protected void transformEnvironment(Environment e)