ERATO Proceedings Istanbul 2006.pdf - Odeon

2 Crowd Engine Resume
The crowd engine which is also called VRCrowd has as a goal to render and animate at least 1000
digital actors in real time. It is responsible for updating the animation and to render the spectators.
The input needed per template [Ulicny2004] is two or three meshes with decreasing level of detail,
four or more different textures that have different clothing styles and color key areas described in
their alpha channels [deHeras2005,deHerasVSMM2005]. Given this data the VRCrowd engine can
start rendering the humans, but still we need scripting and scenarios as well as audio to make the
experience complete. In collaboration with the Danish Technical University (DTU) we defined
camera placements for audio recordings that have the characteristics of that specific listening
location. This process is called auralization, described in [Lisa2004] and relies on a sound wave ray
tracing. The engine has come a long way since we started the project and its first apparition was in
[Ulicny2004]. We were then using static key-framed meshes and simple whole mesh color variety.
At the end of the project we have fully dynamic animation and per texel accurate color modulation
[deHeras2005].
Variety comes through textures and modifiable color areas. These areas defined by the artist in each
texture for each color area such as the dress, jewels and hair. Each of these areas can then be
modified individually and their color ranges are described in an HSB space as detailed in our work
[deHeras2005]. Examples of this variety can be seen in the Fig 1, where there are 4 different
templates visible: two for the patricians and noblemen. The nobles have four textures per template
and the patricians have eight and using the color variety on each such texture we get a greater effect
of variety. This means we work very little on creating variety and spend more time on scenario
authoring and tuning.
To be able to have smooth animation transitioning and updates we have all animation clips stored as
quaternions and interpolate the key frames using spherical linear interpolation for each individual in
the crowd for each animation that is active. To further smooth the interpolation when transitioning
we use a cosine function to weight which animation clip is being more important.
With the use of programmable graphics hardware we deform the mesh in the vertex shader and light
it with Phong shading and apply the color variety at fragment level. This was extensibly described in
[deHeras2005].