Autodesk LIGHTSCAPE, Manual

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Reflection Model for Radiosity
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Reflection Model for Radiosity
Lightscape uses this reflection model only for radi-
osity processing, not for displaying an image. This
model has the following capabilities:
• Diffuse reflection
•
Specular transmission
• Correct texture handling.
For radiosity computations, Lightscape assumes the
surface is an ideal diffuse (lambertian) surface. If the
surface is transparent, light makes it through the
surface and is attenuated by the color of the surface.
This results in colored shadows being cast by trans-
parent surfaces.
This reflection model has the following limitations:
• No refraction of transmitted light
• No specular reflection from shiny objects
• No diffuse transmission.
Transparent surfaces do not refract the transmitted
light. It is not possible with the radiosity process to
create a lens and have it focus the transmitted light
into a bright spot. It is also not possible to have a
mirror reflect a bright spot of light onto another
surface— sometimes referred to as caustics.
Reflection Model for OpenGL
Display
The reflection model used during OpenGL display is
very similar to the one used during radiosity
processing. It has the following capabilities:
• Diffuse reflection
• Specular transmission.
All surfaces are displayed as diffuse and anything seen
through a transparent surface is attenuated by the
color of the surface.
This reflection model has the following limitations:
• No refraction of transmitted light
• No specular reflection from shiny objects
• No diffuse transmission
• Incorrect display of intensity of textured surfaces.
Transparent surfaces do not refract light. For
example, there is no distortion when looking through
a curved piece of glass.
OpenGL was designed to take advantage of hardware
acceleration, causing two further limitations. The
mapping from physical units to the limited range of
values used by the hardware can only be done before
applying the texture. Consequently, textures are not
displayed at the correct intensity during interactive
display. In general, this causes texture-mapped
surfaces to appear too dark during OpenGL display.
The other limitation is that the OpenGL libraries use
blending to handle transparency. For this reason,
there can be significant loss of precision if several
transparent surfaces overlap. These limitations are
not significant if interactivity is desired.
Ray Tracing Reflection Models
Ray tracing works by tracing rays from the eye into
the environment. Ray tracing in this way handles
reflections and refraction through transparent
surfaces. For more information about ray tracing,
refer to Chapter 14, “Rendering.”
There are two reflection models you can use with the
ray tracer:
• OpenGL-compatible reflection model