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3. Real-Time One-Bounce Indirect Illumination and Shadows using Ray Tracing 169
{
f l o a t 3 f 3 I L = ( 0 . 0 f ) . xxx ;
// lo op o v e r VPL k e rn el
for ( f l o a t row = −SFS ; row <= SFS ; row += 6 . 0 f ) {
for ( f l o a t c o l = −SFS ; c o l <= SFS ; c o l += 6 . 0 f ) {
// unpack RSM g−b u f f e r data f o r VPL
RSM data d = LoadRSMData ( adr ) ;
// compute w e i g h t i n g f a c t o r f o r VPL
f l o a t f = evaluateVPLWeightingFac ( d , f3CPos , f3CN ) ;
i f ( f > 0 .0 f ) {
f 3 I L += tr a c e Ra yL i n k ed Tr i s ( f3CPos . xyz , f3D )∗
∗ d . f3 C ol ∗ f ;
}
}
}
// am p li f y t he accumulated b lo c k e d i n d i r e c t l i g h t a b i t
// to make i n d i r e c t shadows more prominent
return 1 6 . 0 f ∗ f 3 I L ;
}
// r e n d e r s th e accumulated c o l o r o f b l o c ke d l i g h t u s i n g a 3D
// g r id o f t r i a n g l e l i s t s t o d e t ec t o cc l ud e d VPLs
f l o a t 4
PS R e n d er B l o ck e d I n d i r ec t L i g h t L in k e d T r i s ( PS SIMPLE INPUT I ) :
SV TARGET
{
i n t 3 t c = i n t3 ( i nt 2 ( I . vPos . xy ) << 1 , 0 ) ;
i n t 2 i 2O f f = ( i n t 2 ( I . vPos . xy ) % (0 x5 ) . xx ) ;
Gbuf data d = LoadGBufData ( t c ) ;
// tr a n s f o r m world s p a c e pos t o rsm t e x t ur e sp ac e
f l o a t 2 r t c = transform2RSMSpace ( d . f3CPos ) ;
f l o a t 3 f 3 IS = 0 . 0 f ;
f l o a t 3 f 3 I L = g t x I n d i r e c t L i g h t . SampleLevel (
g SamplePointClamp , I . vTex . xy , 0 ) . xyz ;
// i s any i n d i r e c t l i g h t ( phase 1) r e a c h i n g t h i s p i x e l
[ branch ] i f ( dot ( f3I L , f 3 I L ) > 0 .0 f )
f 3 I S = c o m pu t e Bl o c ke d I n d i r e c t L i g h t ( r t c , i 2 Of f ,
d . f3CPos , d . f3CN ) ;
return f l o a t 4 ( f3 I S , 0 . 0 f ) ;
}
Listing 3.3. Accumulating blocked indirect light.
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170 III Global Illumination Effects
Figure 3.6. Demo scene with indirect illumination and indirect shadows.
Again, the dithered, blocked indirect light is blurred and upsampled using
a bilateral filter. After that, the blocked indirect light is subtracted from the
indirect light, and the result is clamped to make sure that indirect illumination
doesn’t become negative. This generates the full indirect illumination approxi-
mation with indirect shadowing. Finally, indirect illumination is combined with
direct illumination and shadowing to produce the final image as shown in Fig-
ure 3.6.
The performance for rendering the full one-bounce indirect illumination, in-
cluding indirect shadows with tracing nine rays per pixel is at 70–110 fps for a
32×32×32 grid and a resolution of 1280×800 on an AMD HD5970. The number
of blocker triangles that get inserted into the 3D grid in every frame is in the
order of 6000.
3.6 Future Work
There are several future directions for improving the techniques described in this
chapter.
1. The use of a hierarchical grid for speeding up ray-triangle intersections.
2. The insertion of references to a hierarchical structure, for example., a kd-
tree (encoded in a buffer) into the lists of each grid cell. This would allow
for faster ray-tracing of rigid or static scene elements.
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3. Real-Time One-Bounce Indirect Illumination and Shadows using Ray Tracing 171
3. The use of a binary 3D grid that could be generated by a scattering pixel
shader and the use of the SM5 instruction for an atomic binary or opera-
tion (InterlockeOr()). Early experiments show that this is feasible and
fast, but the resulting blocked indirect light is not stable for low enough
resolutions of the binary 3D grid.
4. Instead of computing the accumulated contribution of blocked VPLs for
each pixel, it would be possible to compute a spherical harmonics projection
of the blocked indirect light of a distribution of VPLs at the center of each
cell of the 3D grid. For a given screen pixel one could reconstruct a smooth
approximation of the blocked indirect light from the tri-linear interpolation
of eight sets of the spherical harmonics coefficient of the eight relevant grid
cells.
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