Texture and Light for Architectural Exteriors - 3D for Graphic Designers - page 404

and some reflection) and move on to other tasks, but by taking a few things into consideration, you can add
some realism to the glass.
In real glass, the values for transparency and reflectivity are directly tied to the index of refraction. The
higher the refractive value, the higher the reflectivity. As the reflectivity increases, the transparency de-
creases (these two values add up to 100%). An additional consideration is the Fresnel effect. As the incid-
ence angle of the surface increases relative to the viewer, the reflectivity increases to eventually reach 100%
when the surface is parallel to the viewer. Fortunately, this is not difficult to set up after the correct reflective
value is derived. To avoid a lengthy explanation of the math behind this, the reflection amount for typical
glass is about 4.2%, so setting up the rest is relatively simple:
1. Set the Specular Amount to 4.2% and the Fresnel option to 100%.
2. Enable Match Specular so that the reflective values will fill automatically.
3. Enable Conserve Energy. This keeps the balance between reflective and transparent values and takes
the Fresnel effect into account automatically.
4. In Material Trans, set the Transparent Amount to 95.8% (100% minus the Reflective Amount).
5. Set the Absorption Distance to 5 mm.
6. Enter a Refractive Index of 1.52, which is common for glass.
Set like this, your glass material will behave mostly like real glass and should appear like the image
shown in Figure 11-21 .
Figure 11-21: The completed glass material decreases in reflectivity as the incidence angle increases.