Pixie Scene Renderer Anurak Thungtong and Remo Mueller

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Pixie Scene RendererAnurak Thungtong and Remo
Mueller
Caustic Rendering and Irradiance Caching To
create caustic maps and global illumination maps
in Pixie, it is necessary to create a two pass
program. The first pass generates the irradiance
cache, which we will call the caustic map,
because irradiance caches can be used for other
purposes as well. To the right, we can see a
simple boxand the caustic effect it creates on
thematte surface which is next to itself. We
can also include other objects into the scene
which reflect off of the box surface, which in
this case is a mirror. Notice that the spheres do
not cast their own caustic reflections. The
caustic reflection of an object can be specified
by the attributes for each given object and for
each surface.
What is Pixie? Pixie is one of many open source
graphics renderer that uses Pixar's Renderman
language to create graphics. Pixie can render
scenes that are constructed using .rib scene
files, and .sl shader files.
Multipass Rendering
Ambient
Diffuse
Specular
What is RenderMan? RenderMan is a 3D scene
description language published by Pixar. It is
divided in to two parts, The Ri API or RIB and
Shading Language. Note that RenderMan is the
standard, not the renderer. RIB is a language
that describes the scene to a renderer such as
the position, dimension, or color of the object
or the position and direction of light source.
The Shading Language or SL is responsible for
defining the appearance of object surface,
lights, and atmospheric events. Texture
Mapping An effect that can be easily
incorporated using RenderMan is texture mapping.
Textures can easily be passed into shader files
in the format of .tx files. The Shading Language
can then interpret these texture files and then
correctly apply them to whichever surface theyre
working with. Heres an example of applying a
simple wood- grain texture file to a surface.
Final Result
Multipass rendering can be easily implemented
using the Pixie Renderer. To do this, a couple
of global variables are set using the Declare
command inside of the RIB file. These variables
are then passed in and out of the shader to
separate the scenes into different output files.
These output files can be seen above. Multipass
rendering isnt limited to lighting, but can be
passed on to all the various attributes that
exist in an RIB file. Multipass rendering is a
useful method to debugging code inside of Pixie.
Subsurface Scattering Subsurface Scattering can
be implemented inside of Pixie using ray tracing.
However, using ray tracing to implement
subsurface scattering is a very expensive method,
and unless you have a large amount of powerful
processors at hand, it isnt the best way to
implement subsurface scattering. Subsurface
Scattering can be implemented using depth maps.
Although this method doesnt follow the way
subsurface scattering works in science, it
creates a very good effect that is very similar
to subsurface scattering. This approach has been
successfully used in movies such as the skin
effect for Gollum.
Finally we alter some details of the spheres and
of the box. The spheres no cast their own
caustic reflections, but at the same time, they
block the caustic map created by the box. The
box has different properties an in this case it
is a green glass prism that creates a caustic map.
2006 Case Western Reserve