Graphics Reference
In-Depth Information
Fig. 11.2
This model has 2,348 triangles and two 512 × 512 texture maps. One is a diffuse
color map; the other is a normal map (Image courtesy of Andrius Drevinskas)
make any of these model types convincing because of their complexity. Instead,
shaders are used to generate geometry at render time. These are
geometry shaders
(Bailey and Cunningham
2008
). To make a geometry shader, the subject must be
studied closely so that it may be reproduced accurately by algorithms with very
little user input.
Some geometry shaders are so use-specifi c that they cannot be expected to be
used often outside the original context, such as the feather shader used in the movie
Stuart Little 2
for a bird character. Others are more generically applicable and can
be found in some form on many fi lm and video game projects.
11.3.1
Hair
It is possible to build hair into a model without the use of a hair shader, but this is
ordinarily done due to technical limitations rather than aesthetic reasons. Before the
invention of hair shaders, a character's hair was normally carved into the model like
every other feature. Hair made in this way is rigid and unnatural, even when an
attempt is made to animate it. Another method is to make layers of opacity mapped
polygons, where each polygon represents a quantity of hair. This method is com-
mon in video games made after 2003 and is still in use in 2012. The result isn't as
convincing as a true hair shader (Hadap et al.
2007
; Lin et al.
2011
), but is a fair
approximation for a low cost in memory and rendering time. It has recently become
possible to render hair shaders in real time, making it likely that they will become
more common in video games (Xing et al.
2012
).
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