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Wenzel Jakob 2011-07-07 23:06:43 +02:00
parent ff62ccea31
commit 37770752ca
4 changed files with 72 additions and 40 deletions
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18
data/tests/test_bsdf.xml
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@ -2,15 +2,6 @@
to be tested for consistency. This is done
using the testcase 'test_chisquare' -->
<scene>
<!-- Test the rough dielectric model with the anisotropic
Ashikhmin-Shirley microfacet distribution -->
<bsdf type="roughconductor">
<string name="preset" value="Au"/>
<string name="distribution" value="as"/>
<float name="alphaU" value="0.1"/>
<float name="alphaV" value="0.3"/>
</bsdf>
<!-- Test the diffuse model -->
<bsdf type="diffuse"/>
@ -97,4 +88,13 @@
<string name="distribution" value="beckmann"/>
<float name="alpha" value=".3"/>
</bsdf>
<!-- Test the rough dielectric model with the anisotropic
Ashikhmin-Shirley microfacet distribution -->
<bsdf type="roughconductor">
<string name="preset" value="Au"/>
<string name="distribution" value="as"/>
<float name="alphaU" value="0.1"/>
<float name="alphaV" value="0.3"/>
</bsdf>
</scene>

17
src/bsdfs/microfacet.h
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@ -318,8 +318,21 @@ public:
* \param alpha The surface roughness
*/
Float G(const Vector &wi, const Vector &wo, const Vector &m, Float alphaU, Float alphaV) const {
Float alpha = std::max(alphaU, alphaV);
return smithG1(wi, m, alpha) * smithG1(wo, m, alpha);
if (m_type != EAshikhminShirley) {
return smithG1(wi, m, alphaU)
* smithG1(wo, m, alphaU);
} else {
/* Infinite groove shadowing/masking */
const Float nDotM = std::abs(Frame::cosTheta(m)),
nDotWo = std::abs(Frame::cosTheta(wo)),
nDotWi = std::abs(Frame::cosTheta(wi)),
woDotM = absDot(wo, m),
wiDotM = absDot(wi, m);
return std::max((Float) 0, std::min((Float) 1,
std::min(2 * nDotM * nDotWo / woDotM,
2 * nDotM * nDotWi / wiDotM)));
}
}
std::string toString() const {

16
src/bsdfs/roughconductor.cpp
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@ -41,29 +41,29 @@ MTS_NAMESPACE_BEGIN
* \begin{enumerate}[(i)]
* \item \code{beckmann}: Physically-based distribution derived from
* Gaussian random surfaces. This is the default.
* \item \code{ggx}: New distribution proposed by
* Walter et al. \cite{Walter07Microfacet}, which is meant to better handle
* the long tails observed in measurements of ground surfaces.
* Renderings with this distribution may converge slowly.
* \item \code{phong}: Classical $\cos^p\theta$ distribution.
* Due to the underlying microfacet theory,
* the use of this distribution here leads to more realistic
* behavior than the separately available \pluginref{phong} plugin.
* \item \code{ggx}: New distribution proposed by
* Walter et al. meant to better handle the long
* tails observed in measurements of ground surfaces.
* Renderings with this distribution may converge slowly.
* \item \code{as}: Anisotropic Phong-style microfacet distribution proposed by
* Ashikhmin and Shirley \cite{Ashikhmin2005Anisotropic}.\vspace{-3mm}
* \end{enumerate}
* }
* \parameter{alpha}{\Float\Or\Texture}{
* Specifies the roughness value of the unresolved surface microgeometry.
* Specifies the roughness of the unresolved surface microgeometry.
* When the Beckmann distribution is used, this parameter is equal to the
* \emph{root mean square} (RMS) slope of the microfacets. This
* parameter is only valid when \texttt{distribution=beckmann/phong/ggx}.
* \default{0.1}.
* }
* \parameter{alphaU, alphaV}{\Float\Or\Texture}{
* Specifies the anisotropic rougness values along the tangent and bitangent directions. These
* parameter are only valid when \texttt{distribution=as}.
* \default{0.1}.
* Specifies the anisotropic rougness values along the tangent and
* bitangent directions. These parameter are only valid when
* \texttt{distribution=as}. \default{0.1}.
* }
* \parameter{preset}{\String}{Name of a material preset, see
* \tblref{conductor-iors}.\!\default{\texttt{Cu} / copper}}

61
src/bsdfs/roughdielectric.cpp
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@ -38,29 +38,29 @@ MTS_NAMESPACE_BEGIN
* \begin{enumerate}[(i)]
* \item \code{beckmann}: Physically-based distribution derived from
* Gaussian random surfaces. This is the default.
* \item \code{ggx}: New distribution proposed by
* Walter et al. \cite{Walter07Microfacet}, which is meant to better handle
* the long tails observed in measurements of ground surfaces.
* Renderings with this distribution may converge slowly.
* \item \code{phong}: Classical $\cos^p\theta$ distribution.
* Due to the underlying microfacet theory,
* the use of this distribution here leads to more realistic
* behavior than the separately available \pluginref{phong} plugin.
* \item \code{ggx}: New distribution proposed by
* Walter et al. meant to better handle the long
* tails observed in measurements of ground surfaces.
* Renderings with this distribution may converge slowly.
* \item \code{as}: Anisotropic Phong-style microfacet distribution proposed by
* Ashikhmin and Shirley \cite{Ashikhmin2005Anisotropic}.\vspace{-3mm}
* \end{enumerate}
* }
* \parameter{alpha}{\Float\Or\Texture}{
* Specifies the roughness value of the unresolved surface microgeometry.
* Specifies the roughness of the unresolved surface microgeometry.
* When the Beckmann distribution is used, this parameter is equal to the
* \emph{root mean square} (RMS) slope of the microfacets. This
* parameter is only valid when \texttt{distribution=beckmann/phong/ggx}.
* \default{0.1}.
* }
* \parameter{alphaU, alphaV}{\Float\Or\Texture}{
* Specifies the anisotropic rougness values along the tangent and bitangent directions. These
* parameter are only valid when \texttt{distribution=as}.
* \default{0.1}.
* Specifies the anisotropic rougness values along the tangent and
* bitangent directions. These parameter are only valid when
* \texttt{distribution=as}. \default{0.1}.
* }
* \parameter{intIOR}{\Float\Or\String}{Interior index of refraction specified
* numerically or using a known material name. \default{\texttt{bk7} / 1.5046}}
@ -89,25 +89,44 @@ MTS_NAMESPACE_BEGIN
* {bsdf_roughdielectric_textured.jpg}
* }
*
* This plugin is essentially the ``roughened'' equivalent of the plugin
* \pluginref{dielectric}. As the roughness parameter $\alpha$ decreases, it
* will increasingly approximate the smooth model. The implementation of this
* plugin is based on the paper ``Microfacet Models for Refraction through
* Rough Surfaces'' by Walter et al. \cite{Walter07Microfacet}. It supports
* several types of microfacet distributions and has a texturable roughness
* parameter. Exterior and interior IOR values can be independently
* specified, where ``exterior'' refers to the side that contains the surface
* normal. Similar to the \pluginref{dielectric} plugin, IOR values can either
* be specified numerically, or based on a list of known materials (see
* This plugin is essentially the ``roughened'' equivalent of the (smooth) plugin
* \pluginref{dielectric}. For very low values of $\alpha$, the two will
* be very similar, though scenes using this plugin will take longer to render
* due to the additional computational burden of tracking surface roughness.
*
* The implementation of this plugin is based on the paper ``Microfacet Models
* for Refraction through Rough Surfaces'' by Walter et al.
* \cite{Walter07Microfacet}. It supports several different types of microfacet
* distributions and has a texturable roughness parameter. Exterior and
* interior IOR values can be independently specified, where ``exterior''
* refers to the side that contains the surface normal. Similar to the
* \pluginref{dielectric} plugin, IOR values can either be specified
* numerically, or based on a list of known materials (see
* \tblref{dielectric-iors} for an overview). When no parameters are given,
* the plugin activates the default settings, which describe a borosilicate
* glass BK7/air interface with a light amount of roughness modeled using a
* Beckmann distribution.
*
* To get an intuition about the range and effects of the surface roughness
* parameter $\alpha$, consider the following: a value of
* $\alpha=0.001-0.01$ corresponds a material with slight imperfections on an
* otherwise smooth surface finish, $\alpha=0.1$ is relatively rough,
* and $\alpha=0.3-0.5$ is \emph{extremely} rough (e.g. a etched or ground
* finish).
*
* When using the Ashikmin-Shirley or Phong models, a conversion method is
* When using the Ashikhmin-Shirley or Phong models, a conversion method is
* used to turn the specified $\alpha$ roughness value into the exponents
* of these distributions. This is done in a way, such that the different
* distributions all produce a similar appearance for the same value of $\alpha$.
* distributions all produce a similar appearance for the same value of
* $\alpha$.
*
* The Ashikhmin-Shirley microfacet distribution allows the specification
* of two distinct roughness values along the tangent and bitangent
* directions. This can be used to provide a material with a ``brushed''
* appearance. The alignment of the anisotropy will follow the UV
* parameterization of the underlying mesh\footnote{Therefore,
* such anisotropic materials cannot be applied to triangle meshes that
* are missing texture coordinates.}.
*
* When using this plugin, it is crucial that the scene contains
* meaningful and mutally compatible index of refraction changes---see
@ -116,7 +135,7 @@ MTS_NAMESPACE_BEGIN
* not always a perfect a perfect match to the underlying scattering distribution,
* particularly for high roughness values and when the \texttt{ggx}
* microfacet distribution is used. Hence, such renderings may
* converge slowly.\vspace{1cm}
* converge slowly.
*
* \begin{xml}[caption=A material definition for ground glass, label=lst:roughdielectric-roughglass]
* <bsdf type="roughdielectric">