Graphics Reference
In-Depth Information
Color
Shininess
Material type textures
Grass
Dirt
Normals
Heights
Rust
Iron
Stone
Wood
Figure 3.10.
Composed textures (left), textures associated with the material types
(center), composed aged chest (right). While the left side of the model is aged only
slightly the amount of rust, dirt, and organic material increases to the right.
Depending on the needs of the artists or production standards, the composition
processes might need to be adapted and further material information might need
to be exported. For preview rendering purposes, we used the Phong reflection
model and used the same output textures for a high-quality rendering in a DCC
tool (see Figure 3.1). The initial material on the surface is already visually rep-
resented in the original diffuse texture. Thus, for compositing we only need to
consider the amount of newly added material by taking the difference between
the currently present material
m
curr
and the initial material
m
init
. To assemble
the resulting diffuse color, we blend the original surface texture with color tex-
tures
s
i
representing the individual material types (see Figure 3.10, center). The
appearance pattern of the deposited material color
c
deposit
is controlled by a base
strength
b
i
and a random variation
v
i
:
c
deposit
=
i
max(0
,
m
curr,i
−
m
init,i
)
·
s
i
·
(
b
i
+
v
i
· ξ
i
)
,
whereas
ξ
i
denotes a uniformly destributed random number. This allows modeling
a wider range of appearances, including homogeneous patina of copper or noisy
rust stains on iron surfaces.
The resulting diffuse color is computed by the weighted sum of the deposited
colors of all material types:
c
diffuse
=lerp
c
org
,
c
deposit
,
saturate
i
ξ
i
)
.
(
b
i
+
v
i
·
The shininess is estimated similarly, leaving out the color textures. The height
map is computed based on the amount of material resting on the surface, which
is then used in a second pass to estimate surface normals from neighboring texels.
The parameters of the composition can be changed during or after the simulation.
