Graphics Reference
In-Depth Information
Floating
Floating
Bounce
event
Miss
Floating
Fall down
Fall down
Figure 3.8.
The visible course (
•
) of a gammaton floating around an overhang (left) and
when dripping off a cliff (right). In the first, the gammaton on the right falls due to a
bounce event. In the latter, the blue dashed ray misses and in response the gammaton
falls down.
gammaton are sequentially updated. First, the gammatons are splatted into the
material atlas to deposit material. Afterwards, a separate transform feedback
pass is executed to update the material of the gammatons. (Modern graphics
APIs allow for unordered access from all shader stages, making it possible to
implement both update procedures in one pass. Legacy implementations require
two separate steps.)
Determining transfer rates.
The amount of material that is picked up depends first
on the material type, for instance, to accommodate that water is more volatile
than stone, and second on the material already present on the surface. The
initial material on the surfaces is assigned by presets. The coecients required
for modeling volatileness
g_volatileness
are stored per material and can be part
of an asset library. They are set once prior to the simulation for each material
and can be stored and reused in other scenes. At runtime one degree of freedom
remains: the pick-up ratio
g_pickUpRatio
between the amount of material picked
up from the surface and added to the gammaton (and vice versa). A ratio of
zero means that material is only picked up, whereas a ratio of one means all is
dropped. Naturally, we obtain material preservation if this ratio is 1:1. Exposing
this ratio to the artist allows both to speed up the aging process and to reverse
it by washing away material, i.e., picking up more material than depositing (see
Figure 3.9).
The amount of material to transfer is determined by the method in Listing 3.5.
