Theatre Design & Technology - Spring 2010 - 46

of the box will appear smooth between all the various vertices.
Figure 4 shows the same vR simulation rendered using vector
lighting. Note the jagged edges of the shadows. This technique
of lighting is somewhat more interactive than light mapping.
Materials can be changed easily. One can swap wood for stone
and the lighting effects will still exist. However the lighting itself cannot be changed unless one goes back to the original
model, relights it and reassigns the lighting qualities to every
vertex. vector lighting is somewhat more processor intensive
than texture rendering because of the hundreds or thousands
of additional vertices. The computer has to slow down to accommodate this increase in geometry and render it in real-time
frame rates. Figure 5a is an image of the boathouse model
showing a normal number of vertices. Figure 5b shows how
an additional number of vertices added in vertex lighting can
achieve a somewhat smoother look to the lighting.
An effective way of achieving lighting simulations that are
both detailed and interactive is to combine methods. One of
those combined methods is to combine light-mapping (painting
the surfaces with basic shadows, lights, and color) with stencil
shadows that are created by the vR application itself. This gives
you some lights that are predetermined and can't be changed and
others, a few of the more important lights, which can be added
to the vR simulation and are therefore interactive and can be
moved about. The high quality of the light-mapped textures
offsets the more simplistic look of the stencil shadows for a

satisfying simulation in which the most important lights remain
interactive.
Finally, the most advanced form of lighting within a vR
simulation-the holy grail of real-time rendering-is called
real-time radiosity or radiance rendering. Radiance rendering
consists of analyzing the resulting picture on the screen pixel
by pixel and defining the lighting for every single part of the
picture. It does this by analyzing not only what light is coming
from obvious light sources but what light is being reflected by
all the other surfaces. Therefore, if a strong light hits a glossy
red wall, the wall itself emits red light causing a red glow to fall
on objects that are close to that wall. In order to achieve realtime radiosity in a vR simulation many short cuts have to be
taken in the programming. In this case very few light sources
can be used because every surface that those lights hit becomes
a light source in itself. The direction of light is determined by
the angle at which the original light hits it and the color is determined by the color of the object in combination with the
color of the light. Also, the intensity of the light is determined by
the reflectivity or glossiness that has been pre-determined for
that particular object and the materials that are painted onto
that object. For example marble might be more reflective and
therefore emit a stronger light than wood. In real-time simulations it is possible to achieve lighting that is nearly photo realistic using real-time radiosity. Figure 6 shows the same setting
for Talley's Folly rendered with real-time radiosity and a single

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Table of Contents for the Digital Edition of Theatre Design & Technology - Spring 2010