Graphics Reference
In-Depth Information
converting from clip space into screen space [0
,
1] range, as we can see below:
P
cs
=(
P
vs
+
Reflect
(
V
vs
, N
vs
))
∗
M
proj
,
P
ss
=
P
cs
P
cs
w
∗
[0
.
5
−
0
.
5] + [0
.
50
.
5]
.
Once we have a screen-space reflection vector, we can run the Hi-Z traversal
to ray-march along the acceleration structure using
O
,
D
,and
t
.
We'll first look at the pseudo code in Listing 4.2. The algorithm uses the
Hi-Z buffer we constructed earlier to accelerate the ray marching. To visualize
the algorithm in Listing 4.2 step by step, follow Figure 4.12.
Once the ray-tracing algorithm has run, we have our new coordinate in screen
space that is our ray intersection point. Some ideas are borrowed from displace-
ment mapping techniques found in the literature [Hien and Lim 09, Hrkalovic and
Lundgren 12, Oh et al. 06, Drobot 09, Szirmay-Kalos and Umenhoffer 06]. One
major difference is that we start on the root level while displacement techniques
start on the leaf level for marching a ray. Ray-marching with a view-space Z-buffer
is a bit more involved because we have to manually interpolate the Z-coordinate
as it is not possible to interpolate it in screen space.
level
=0
// starting level to traverse from
while
level not below N
// ray
−
trace until we descend below the
// root level defined by N, demo used 2
minimumPlane
=
getCellMinimumDepthPlane
(...)
// reads from the Hi
−
Z texture using our ray
boundaryPlane
=
getCellBoundaryDepthPlane
(...)
// gets the distance to next Hi
−
Z cell boundary in ray
// direction
closestPlane
=
min
(
minimumPlane
,
boundaryPlane
)
// gets closest of both planes
ray
=
intersectPlane
(...)
// intersects the closest plane , returns O + D
tonly.
if
intersectedMinimumDepthPlane
// if we intersected the minimum plane we should go down a
// level and continue
descend a level
if
intersectedBoundaryDepthPlane
// if we intersected the boundary plane we should go up a
// level and continue
ascend a level
color
=
getReflection
(
ray
)
// we are now done with the Hi
−
Zray
// marching so get color from the intersection
Listing 4.2.
Pseudo code for implementing the Hi-Z ray tracing.
