Graphics Reference
In-Depth Information
Cascade 1
Cascade 2
Cascade 3
Cascade 1
Cascade 2
Cascade 3
(a)
(b)
Figure 3.4.
(a) Initial rays for each sunlight cascade. Red shows where the cascade is not being rendered
due to depth test failure. (b) Ray march samples for each sunlight cascade. Red crosses show where we
break out of the ray-march loop.
In Section 3.5 we will describe how we extended the system by using a 3D lookup
texture to control the scattering amount more accurately and more dynamically.
The scattering phase function defines the angular distribution of the scattered
light. The phase function can be used to determine how much of the total scat-
tered light is scattered toward the camera. For the volumetric light effects in
Killzone: Shadow Fall
, we want to simulate the scattering of light by aerosols
like dust, mist, and smoke. The way light is scattered by aerosols is described by
Mie-scattering. Mie-scattering shows that light will scatter more in the forward
direction when scattered by bigger particles in the atmosphere (Figure 3.5). To
approximate the Mie-scattering phase function, we use the Henyey-Greenstein
phase function [Henyey and Greenstein 41]:
g
)
2
(1
−
f
HG
(
θ
)=
cos
(
θ
))
3
/
2
.
(3.1)
4
π
·
(1 +
g
2
−
2
g
·
The
g
value in Equation (3.1) controls how much light will scatter in the forward
direction (Figure 3.6). This value should actually be based on the type of particles
Mie scattering caused by
large particles
Light direction
Figure 3.5.
Mie-scattering: light scatters more in the forward direction when scattered
by bigger particles.
