de.grogra.ray.physics

Interface Shader

All Superinterfaces:

Scattering

All Known Subinterfaces:

Shader

All Known Implementing Classes:

AlgorithmSwitchShader, IORShader, Material, MaterialRef, Phong, RGBAShader, ShaderRef, SideSwitchShader, SunSkyLight, SwitchShader

public interface Shader
extends Scattering

A Shader instance represents a surface shader which calculates the color of an outgoing light ray at a given point as a function of geometrical and optical properties, namely local and global point coordinates, canonical uv-coordinates, surface tangent vectors, outgoing ray direction, index of refraction, and a list of incident light rays, consisting of color and direction.

Author:

Ole Kniemeyer

Field Summary

Fields

Modifier and Type	Field and Description
static float	LAMBERTIAN_VARIANCE The angular variance of a lambertian reflector, (π2 - 4) / 8.

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

Methods

Modifier and Type	Method and Description
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.
boolean	isTransparent()
void	shade(Environment env, RayList in, Vector3f out, Spectrum specOut, Tuple3d color) Computes color of outgoing light ray for given input.

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

computeBSDF, generateRandomRays, getAverageColor, getFlags

Field Detail

LAMBERTIAN_VARIANCE

static final float LAMBERTIAN_VARIANCE

The angular variance of a lambertian reflector, (π² - 4) / 8.

See Also:

computeMaxRays(de.grogra.ray.physics.Environment, javax.vecmath.Vector3f, de.grogra.ray.physics.Spectrum, de.grogra.ray.util.Ray, javax.vecmath.Tuple3f, de.grogra.ray.util.Ray, javax.vecmath.Tuple3f), Constant Field Values

Method Detail

computeMaxRays

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. 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 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.

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

isTransparent

boolean isTransparent()

shade

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

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.

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