Graphics Reference
In-Depth Information
Figure 1.2.
Visual disparity between the light
shape and Blinn-Phong specular reflection.
Figure 1.3.
Specular reflection matches the light
shape using the proposed model.
Another way of solving the problem involves switching to global illumination-
based solutions. Several systems were already implementedincommercialen-
gines, mostly voxel based [Mittring 12]; however, they can't fully substitute for
analytical lights, due to stability, resolution, or quality difference.
During our research on a new iteration of the
Killzone
engine for next gener-
ation platform, we wanted to leverage current knowledge about lighting models
and extend it to cover non-point-based lights. A unified way to deal with art
production was also our priority. With our transition to physically based mate-
rial modeling, we also wanted to have physically based lights, using real-world
radiometric quantities, thus achieving a predictable shading model.
We decided to utilize existing BRDFs to model surface reaction to light and
remodel the way lighting information is actually provided to those models. Stan-
dard BRDFs assume light incoming from only one direction with intensity given
as a per-light set quantity. When dealing with an area-based light source, we
would have to solve an integral of the lighting model over all points of the light
shape. This can be achieved numerically, but unfortunately that proves unfea-
sible performance-wise in real-time applications. However, parts of that integral
can be calculated analytically using radiometric integrals, while the rest can be
eciently approximated.
