Transcript ACM SIGGRAPH Symposium on Interactive 3D Graphics and Games 21 February, 2010, Washington, USA Anton Kaplanyan1 1Crytek GmbH Carsten Dachsbacher2 2VISUS / University Stuttgart.

ACM SIGGRAPH Symposium on Interactive 3D Graphics and Games
21 February, 2010, Washington, USA
Anton Kaplanyan1
1Crytek
GmbH
Carsten Dachsbacher2
2VISUS
/ University Stuttgart
Motivation
ACM SIGGRAPH Symposium on Interactive
3D Graphics and Games 2010, Washington
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Previous work
Irradiance volumes
Greger et al. 1997
SH Irradiance Volumes
Tatarchuk 2004
Image-Space Photon Mapping
McGuire and Luebke 2009
Multi-resolution Splatting
Nichols and Wyman 2009
PRT: Spherical Harmonics
Sloan et al. 2004
Spherical proxies with
SH Exponentiation
Zhong et al. 2007
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Previous work, continued
Instant radiosity
Keller 1997
VPL visibility
Laine et al. 2007
Ritschel et al. 2008
Many-lights approach
Walter et al. 2005
Hasan et al. 2007
Chevlak-Postavak et al. 2008
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Previous work, continued
Disk-based Color Bleeding
Bunell 2005
Christensen 2008
Finite Element: Antiradiance
Dachsbacher et al. 2007
Microrendering
Ritschel et al. 2010
All techniques above have one or more of the following limitations:
• Precomputed or redundant data (problems with dynamic
and/or editable scenes)
• Not suitable for game production performance-wise
Most of dynamic techniques are without indirect visibility
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Previous work, lattice methods
Light Propagation Maps
Fattal 2009
Lattice-Boltzmann Lighting
Geist et al. 2004
Lattice-Based Volumetric Global
Illumination
Qiu et al. 2007
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Basic idea
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3D Graphics and Games 2010, Washington
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Basic idea
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3D Graphics and Games 2010, Washington
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Basic idea
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3D Graphics and Games 2010, Washington
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Propagation demo
Overview
Sample lit surface elements
Grid initialization
Light propagation in the grid
Scene illumination with the grid
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Light Propagation Volumes
• Use many-lights approach to capture sources
of indirect lighting
• Sample directly lit surfaces and initialize 3D
grid
• Represent directional distribution with
Spherical Harmonics
– Inspired by SH Irradiance Volumes [Tatarchuk04]
• Iterative, local propagation: cell-to-cell
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Secondary Light Sources
Sample lit surface elements
Grid initialization
Light propagation in the grid
Scene illumination with the grid
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3D Graphics and Games 2010, Washington
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Secondary Light Sources
Reflective shadow maps
Depth
Flux
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3D Graphics and Games 2010, Washington
Normal
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Injection
Sample lit surface elements
Grid initialization
Light propagation in the grid
Scene illumination with the grid
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Pipeline
Reflective shadow maps Radiance volume gathering
VPL
VPL
VPL
A set of regularly
sampled VPLs of the
scene from light position
Discretize initial VPL
distribution by the
regular grid and SH
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Light injection into the volume
• Every element of
Reflective Shadow Map
is a secondary lights
• Render as a point
primitive into 3D grid
– Represent flux in Spherical
Harmonics
• Accumulate all VPLs into the grid
• The 3D grid is initialized with
initial reflected light in the end
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Light Propagation
Sample lit surface elements
Grid initialization
Light propagation in the grid
Scene illumination with the grid
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3D Graphics and Games 2010, Washington
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Pipeline
Reflective shadow maps Radiance volume gathering
Iterative propagation
VPL
VPL
VPL
A set of regularly
sampled VPLs of the
scene from light position
Discretize initial VPL
distribution by the
regular grid and SH
ACM SIGGRAPH Symposium on Interactive
3D Graphics and Games 2010, Washington
Propagate light
iteratively going from
one cell to another
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Iterative Light Propagation
• Local cell-to-cell propagation
across the 3D grid
– Iterate till the light travels through
the entire volume
– Similar to SH Discrete Ordinate
Method (used for participating
media illumination)
– Number of iterations depend on the
resolution of the grid
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The propagation iteration
• 6 axial directions of propagation
• Use contour faces as a
propagation wave front
• Integrate source
intensity by the
solid angle to get
incoming flux
for the face f
The propagation iteration
• Use more than 6
directions
– Only 6 direct neighbors
– Compute light
propagation to each
face of neighbors’ cells
– 30 virtual directions
– SHDOM: 27 neighbor
cells = 27 directions
4 directions of
propagation
– good trade-off of
memory bandwidth vs “ray effect”
8 directions of
propagation
• “Ray effect” - light propagates in a set of fictitious directions
Reprojection
• Acquire the incident flux through
the receiving face
• Create a new point light in the
center of receiving cell
– Oriented towards the face
– Causing exactly the same flux as the face received
• Generate clamped cosine lobe in SH basis
similar to injection stage
• Accumulate the resulting SH coefficients into
the destination cell for next iteration
Scene rendering
Sample lit surface elements
Grid initialization
Light propagation in the grid
Scene illumination with the grid
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Rendering
• Look-up grid with trilinear interpolation
• Evaluate the irradiance with cosine lobe of
surface’s normal
• Apply dampening factor
– Compute directional derivative towards normal
– Dampen based on derivative deviation from the
intensity distribution direction
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Results of indirect illumination
Cascaded Light Propagation Volumes
• Motivation: memory and bandwidth
cost is o(N^3) for increase of LPV grid
– Impossible to support large scenes
• Idea: use multiple nested grids to
refine resolution hierarchically
– Do not consider small objects for
large sparse grids
• Transfer propagated lighting from
nested grid to the parent grid
• Illuminate scene similarly to
cascaded shadow maps
• Reduces the number of iterations sufficient per cascade
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Cascaded Indirect Illumination
1 cascade
3 cascades
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Fuzzy Secondary Occlusion
• Introduce a “fuzzy
blocking” between cells
• Use another grid for blocking
• Occlusion is view-dependent
• Projected size of an occluder
is a cosine lobe
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Fuzzy Secondary Occlusion
Scene
• Represent it as SH
• Store into occlusion grid
• Sample surfaces using
rasterization
Camera
view
– Possibly multiple views
• Very similar to light
injection
• Interpolate blocking
linearly in between cells
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Fuzzy Secondary Occlusion
W/o secondary occlusion
With secondary occlusion
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Multiple Bounces
• Idea: use information
from occlusion grid
to compute multiple
indirect reflections
• Reflect light during
each propagation
iteration
• Avoid self-illumination
by injecting reflected
light at safety-distance
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Glossy Reflections
• Idea: Compute incident light
from reflection direction by
marching through LPV grid
• Go few steps back in
propagation time to reduce
light smearing
• 4 cells is sufficient for
moderately glossy objects
• Lookups into multiple
cells prevent discontinuities
in glossy reflections
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Indirect lighting in isotropic
participating media
•
•
•
•
Ray march through the LPV
Accumulate inscattered light
Limited to single-scattering
Step through the whole
grid along view
direction
– Back to front
accumulation
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Timings (Crytek Sponza)
Depends on scene
complexity
Stage
GTX 285, ms
RSM
Rendering
0.16 (256^2)
0.5 (128^2)
0.8 (128^2)
VPL Injection
0.05
0.2
0.4
Occlusion
Injection
0.02
0.15
0.15
Propagation
0.8/1.1/1.4
0.8/1.1/1.5
0.7/1.1/1.4
LPV look-up
2.4
2.0
1.5
3.4/3.7/4.0
3.5/3.8/4.2
3.4/3.8/4.2
32^3 grid size
8 iterations
Depends on
image size
(1280x720)
Total
Xbox 360, ms PS 3, ms
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Results
Reference, 42 min
LPV, 78 fps @GTX285
Reference PBRT, 45 min LPV, 60 fps @GTX285
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Limitations of the method
• Only diffuse inter-reflections
• Sparse spatial and
low-frequency angular
approximations
– Light diffusion: light transport
smears in all directions
– Spatial discretization: visible
for occlusion and very coarse
grids
• Incomplete information for secondary occlusion
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Conclusion
•
•
•
•
Full-dynamic: scene, view, lighting changes
Real-time: GPU- and consoles- friendly
Production-eligible (simple tweaking)
Highly scalable
– proportionally to quality
• Stable, flicker-free
• Supports complex geometry (e.g. foliage)
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Video
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3D Graphics and Games 2010, Washington
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See the paper for more details
We’d like to thank:
Crytek and especially the CEO Cevat Yerli
for giving us an opportunity to make this
research
The whole Crytek R&D department and
artists for help provided
Many people across the industry and
research community for interesting
discussions and provided feedbacks
THANK YOU FOR YOUR ATTENTION
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Backup slide: Small details
• Stability of the solution
– RSM one-texel snapping
– One-cell snapping for LPVs
– Temporal SSAA with reprojection for RSM injection
• Self-illumination and light bleeding
– Half-cell VPL shifting to normal direction during
RSM injection
– Directional derivative in normal direction to
compute a dampening factor
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3D Graphics and Games 2010, Washington
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Backup slide: Console optimizations
• For both consoles
– Store everything in signed QUVW8 format, [-1;1] with
scaling factor
– Use h/w 3D textures and trilinear filtering
• Xbox 360
– Unwrap RT vertically to avoid bank conflicts during
injection
– Use API bug work-around to resolve into a 3D slice
• PlayStation 3
– Use memory aliasing for render into 3D texture
– Use 2x MSAA aliasing to reduce pixel work twice
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Backup slide: Console optimizations II
• Render Reflective Shadow Map
 Usually 128 x 128 is ok
• Inject each pixel into unwrapped
LPV with a swarm of points
 16384 points in one DIP
 Use vertex texture fetch on X360
 Use R2VB on PlayStation 3
• Multi-layered unwrapping
to avoid bank conflicts during
RSM injection on Xbox 360
• All together: 3,0 ms on X360/PS3
Backup slide: Massive Lighting
 Render sliced unwrapped light box
into LPV (spatial overdraw vs
screen-space, maximum 1024x32 pixels)
 Convert light’s radiant intensity into SH
 Shadows are not supported
Light in the Light
Propagation Volume
Coverage in unwrapped render target