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documentation updates for the HK model

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Wenzel Jakob 2011-07-18 14:46:24 +02:00
parent 41a3e0c841
commit a17fed6f5b
3 changed files with 59 additions and 31 deletions
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1
doc/macros.sty
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@ -21,6 +21,7 @@
\newcommand{\Point}{\texttt{point}}
\newcommand{\Texture}{\texttt{texture}}
\newcommand{\BSDF}{\texttt{bsdf}}
\newcommand{\Phase}{\texttt{phase}}
\newcommand{\Unnamed}{\emph{(Nested plugin)}}
\newcommand{\Or}{~~\small or \small}
\newcolumntype{P}[1]{>{\RaggedRight\hspace{0pt}}p{#1}}

6
src/bsdfs/coating.cpp
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@ -30,8 +30,10 @@ MTS_NAMESPACE_BEGIN
* numerically or using a known material name. \default{\texttt{bk7} / 1.5046}}
* \parameter{extIOR}{\Float\Or\String}{Exterior index of refraction specified
* numerically or using a known material name. \default{\texttt{air} / 1.000277}}
* \parameter{thickness}{\Float}{Denotes the thickness of the layer (to model absorption --- should be specified in inverse units of \code{sigmaA})\default{1}}
* \parameter{sigmaA}{\Spectrum\Or\Texture}{The absorption coefficient of the coating layer. \default{0, i.e. there is no absorption}}
* \parameter{thickness}{\Float}{Denotes the thickness of the layer (to
* model absorption --- should be specified in inverse units of \code{sigmaA})\default{1}}
* \parameter{sigmaA}{\Spectrum\Or\Texture}{The absorption coefficient of the
* coating layer. \default{0, i.e. there is no absorption}}
* \parameter{\Unnamed}{\BSDF}{A nested BSDF model that should be coated.}
* }
*

83
src/bsdfs/hk.cpp
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@ -24,54 +24,79 @@
MTS_NAMESPACE_BEGIN
/*!\plugin{hk}{Hanrahan-Krueger BRDF}
/*!\plugin{hk}{Hanrahan-Krueger BSDF}
*
* This plugin is an implementation of the Hanrahan-Krueger scattering model
* \cite{Hanrahan1993Reflection}. This model provides an analytic BSDF that
* accounts for single scattering within thin slabs of scattering media having
* index matched boundaries.
* \parameters{
* \parameter{sigmaA}{\Spectrum\Or\Texture}{Scattering coefficient of the
* layer. \default{2.0}}
* \parameter{sigmaA}{\Spectrum\Or\Texture}{Absorption coefficient of the
* layer. \default{0.05}}
* \parameter{thickness}{\Float}{Denotes the thickness of the layer.
* Should be specified in inverse units of \code{sigmaA} and \code{sigmaS})\default{1}}
* \parameter{\Unnamed}{\Phase}{A nested phase function instance that represents
* the type of scattering interactions occurring within the layer}
* }
*
* It also accounts for $0^{\mathrm{th}}$-order scattered light (i.e. attenuated
* light) that did not scatter within the medium. When used in conjuction with
* the \pluginref{coating} plugin, it can also acount for refraction and reflection
* at the boundaries of the medium when the indices of refraction are mismatched.
* This plugin provides an implementation of the Hanrahan-Krueger BSDF
* \cite{Hanrahan1993Reflection}. This analytic model simulates single scattering
* within a thin index-matched layer filled with a random medium.
* Apart from single scattering, the implementation also accounts for attenuated
* light that passes through the medium without undergoing any scattering events.
*
* This BSDF needs a nested phase function to model the scattering within the
* medium. When no phase function is given, it will use an isotropic one ($g=0$)
* by default. A sample usage is given below:
* This BSDF requires a phase function to model scattering interactions within the
* random medium. When no phase function is explicitly specified, it uses an
* isotropic one ($g=0$) by default. A sample usage for instantiating the
* plugin is given below:
*
* \begin{xml}
* <bsdf type="hk">
* <spectrum name="sigmaS" value="4"/>
* <spectrum name="sigmaA" value="0.1"/>
* <float name="thickness" value="0.5"/>
* <spectrum name="sigmaS" value="2"/>
* <spectrum name="sigmaA" value="0.05"/>
* <float name="thickness" value="1"/>
*
* <phase type="hg">
* <float name="g" value="0.98"/>
* <float name="g" value="0.8"/>
* </phase>
* </bsdf>
* \end{xml}
*
* When \texttt{sigmaS} = \texttt{sigmaA}$\ = 0$, any associated geometry
* will be invisible.
* When used in conjuction with the \pluginref{coating} plugin, it is possible
* to correctly model refraction and reflection at the layer boundaries when
* the indices of refraction are mismatched:
* \begin{xml}
* <bsdf type="coating">
* <float name="extIOR" value="1.0"/>
* <float name="intIOR" value="1.5"/>
*
* The sampling of this BSDF is either with respect to the phase function PDF or
* with the delta transmission function. The weighting between the two is decided
* based on the probability of an event within the medium.
* <bsdf type="hk">
* <spectrum name="sigmaS" value="2"/>
* <spectrum name="sigmaA" value="0.05"/>
* <float name="thickness" value="1"/>
*
* The implementation is based on code by Tom Kamzimier and Marios Papas.
* <phase type="hg">
* <float name="g" value="0.8"/>
* </phase>
* </bsdf>
* </bsdf>
* \end{xml}
*
* Note that when \texttt{sigmaS} = \texttt{sigmaA}$\ = 0$, or when \texttt{thickness=0},
* any geometry associated with this scattering model will be invisible.
*
* The implementation in Mitsuba is based on code by Tom Kazimiers and Marios Papas.
*/
class HanrahanKrueger : public BSDF {
public:
HanrahanKrueger(const Properties &props) : BSDF(props) {
/* Scattering events per scene unit */
m_sigmaS = props.getSpectrum("sigmaS", Spectrum(4.0f));
/* Absorption events per scene unit */
m_sigmaA = props.getSpectrum("sigmaA", Spectrum(0.1f));
/* Scattering coefficient of the layer */
m_sigmaS = props.getSpectrum("sigmaS", Spectrum(2.0f));
/* Slab Thickness in scene units*/
m_d = props.getFloat("thickness",0.5);
/* Absorption coefficient of the layer */
m_sigmaA = props.getSpectrum("sigmaA", Spectrum(0.05f));
/* Slab thickness in inverse units of sigmaS and sigmaA */
m_d = props.getFloat("thickness", 1);
}