96 lines
3.4 KiB
TeX
96 lines
3.4 KiB
TeX
\newpage
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\subsection{Shapes}
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\label{sec:shapes}
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This section presents an overview of the shape plugins that are released along with the renderer.
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In Mitsuba, shapes define surfaces that mark transitions between different types of materials. For instance,
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a shape could describe a boundary between air and a solid object, such as a piece of rock. Alternatively,
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a shape can mark the beginning of a region of space that isn't solid at all, but rather contains a participating
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medium, such as smoke or steam. Finally, a shape can be used to create an object that emits light on its own.
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Shapes are usually declared along with a surface scattering model (named ``BSDF'', see \secref{bsdfs} for details).
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This BSDF characterizes what happens \emph{at the surface}. In the XML scene description language, this might look like
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the following:
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\begin{xml}
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<scene version=$\MtsVer$>
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<shape type="... shape type ...">
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... $\code{shape}$ parameters ...
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<bsdf type="... bsdf type ...">
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... $\code{bsdf}$ parameters ..
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</bsdf>
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<!-- Alternatively: reference a named BSDF that
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has been declared previously
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<ref id="myBSDF"/>
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-->
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</shape>
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</scene>
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\end{xml}
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When a shape marks the transition to a participating medium (e.g. smoke, fog, ..), it is furthermore
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necessary to provide information about the two media that lie at the \emph{interior} and \emph{exterior}
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of the shape. This informs the renderer about what happens in the region of space \emph{surrounding the surface}.
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\begin{xml}
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<scene version=$\MtsVer$>
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<shape type="... shape type ...">
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... $\code{shape}$ parameters ...
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<medium name="interior" type="... medium type ...">
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... $\code{medium}$ parameters ...
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</medium>
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<medium name="exterior" type="... medium type ...">
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... $\code{medium}$ parameters ...
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</medium>
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<!-- Alternatively: reference named media that
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have been declared previously
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<ref name="interior" id="myMedium1"/>
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<ref name="exterior" id="myMedium2"/>
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-->
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</shape>
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</scene>
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\end{xml}
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You may have noticed that the previous XML example dit not make any mention of surface
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scattering models (BSDFs). In Mitsuba, such a shape declaration creates an \emph{index-matched} boundary.
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This means that incident illumination will pass through the surface without undergoing any kind of
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interaction. However, the renderer will still uses the information available in the shape to correctly
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account for the medium change.
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It is also possible to create \emph{index-mismatched} boundaries between media, where some of
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the light is affected by the boundary transition:
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\begin{xml}
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<scene version=$\MtsVer$>
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<shape type="... shape type ...">
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... $\code{shape}$ parameters ...
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<bsdf type="... bsdf type ...">
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... $\code{bsdf}$ parameters ..
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</bsdf>
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<medium name="interior" type="... medium type ...">
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... $\code{medium}$ parameters ...
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</medium>
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<medium name="exterior" type="... medium type ...">
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... $\code{medium}$ parameters ...
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</medium>
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<!-- Alternatively: reference named media and BSDF
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instances that have been declared previously
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<ref id="myBSDF"/>
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<ref name="interior" id="myMedium1"/>
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<ref name="exterior" id="myMedium2"/>
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-->
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</shape>
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</scene>
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\end{xml}
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This constitutes the standard ways in which a shape can be declared.
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The following subsections discuss the available types in greater detail.
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