Graphics Reference
In-Depth Information
The basic grunge map is simply a matter of mixing the two metal textures using the AO pass as a factor.
Figure 4-27
shows the node setup to do this. The Texture Coordinate node ensures that the objects are mapped
byUVcoordinates(UVmappinghasbeensetupinadvance).TheAOpassimagetextureissentthroughanode
to adjust brightness and contrast, enabling more control over the levels of mixing, and then plugs into the factor
socketoftheColorMixnode.TheoutputoftheColorMixnodegivesthediffuseshaderitscolor.Theresulting
rendered object is shown in
Figure 4-28
.
We can take this a bit further. Rather than combining the textures as mere color inputs for a single diffuse
shader,wecanusethecolorforbothadiffuseshaderandaglossy(reflective)shader.Thiswouldbemoreaccur-
ate for metal, because metal is generally not a perfectly matte surface. There is usually quite a bit of specularity
and reflectivity to metal.
On what basis should we mix the diffuse and glossy shaders? Since we're working with a copper texture, we
might consider trying to isolate the red levels in the surface. Redder parts of copper are generally shinier than
the bluer parts.
Figure 4-27
Combining image textures with nodes
