Graphics Reference
In-Depth Information
Fig. 11.22 A well-painted bump map like the one on the left records height information. On the
right , a render of a plane with the bump map applied to it (Map courtesy of Lennart Hillen)
11.5.4.4
Displacement
Although displacement maps are less commonly used today in favor of normal
maps, they are still used, as are bump maps. Both require only single channel images
and so are a great deal less demanding of memory resources and CPU bandwidth,
and both are calculated more quickly. A displacement map is used to create poly-
gons at render time where pixel brightness corresponds to height (Fig. 11.23 ).
11.5.4.5
Normal Maps
Normal maps adjust the way light refl ects off of a polygon based on an RGB
image that is created by projecting the normals of selected high res geometry onto
the UV layout of low res geometry (Fig. 11.24 ). The effect is similar to that of a
bump or displacement map, but with the addition of modifi ed normals. A bump or
displacement map does not change any surface normals, which makes height
changes less smooth than in a normal map.
Creating normal maps requires the creation of both a high and low-res version of
your object. More correctly, it requires a target object, whose texture coordinates
will be used as the basis for the normal map, and an origin object from which sur-
face information will be taken. The origin object is high resolution, and the target
object is low resolution. You then must render the map by selecting the objects and
invoking your application's normal map render tool.
The end result is calculated for you, and will not easily be edited by hand. This
means that if you want to be sure your map is tilable; you have to be careful to make
tilable geometry to begin with. Trying to modify a normal map after your renderer
generates it can be very diffi cult (Fig. 11.24 ).
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