Game Development Reference
In-Depth Information
gives this freedom to the designer, being thus possible to achieve muscle-like
deformations on any part of the virtual character's skin in order to get a realistic
animation.
Both frameworks address streaming animation and provide low-bit-rate com-
pression schemes. Both FBA and SMS allow the above-mentioned compression
methods, frame-based and DCT-based. Moreover, to improve the compression
ratio, SMS supports advanced animation techniques, such as temporal frame
interpolation and inverse kinematics. For both FBA and SMS, the bit-rate of the
compressed stream depends on the movement complexity (number of segments/
joints involved in motion) and generally lies in the range of 5-40 kbps, for a frame
rate of 25fps.
In the FBA framework, the animation stream contains information relative to the
animation of a single human virtual character, while, in the SMS framework, it
is possible to animate several characters by using a unique stream. Moreover,
the SMS supports the definition and animation of generic 2D/3D objects. This
property is very useful when dealing with a scene where a large number of
avatars or generic objects are present.
In SMS animation, more complex computations are required than in the case of
FBA animation. Thus, concerning the terminal capabilities, dedicated 3D hard-
ware or software optimization is well-suited for implementing SMS animation.
However, the SMS deformation mechanism is in line with the development of
graphics APIs and graphics hardware.
The deformation based on the bones and muscles controllers can be applied in
relation with advanced geometry definition techniques, allowing hierarchical
animation. The following section describes such representation techniques
(Subdivision Surfaces and M ESH G RID ) and shows the use of BBA to control the
animation of a synthetic object by affecting its surrounding space.
Hierarchic Animation: Subdivision
Surfaces and M ESH G RID
In this section, methods are presented for performing hierarchical animation,
where the displacement of a number of key points is extended to all vertices
through an automatic iterative construction/displacement scheme. Subdivision
Surfaces and M ESH G RID both achieve this goal, but since M ESH G RID is more
appropriate for defining a “surrounding influence volume” in the skin deforma-
tion control presented in previous section, more attention will be devoted to
M ESH G RID .
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