toward real-time global illumination
DESCRIPTION
Toward Real-Time Global Illumination. Global Illumination == Offline?. Ray Tracing and Radiosity are inherently slow. Speedup possible by: Brute-force: more hardware, multicore…etc. Approximate results. Under Simplified Assumption. Can it become faster if: …the view is fixed? - PowerPoint PPT PresentationTRANSCRIPT
Toward Real-Time Global Illumination
Global Illumination == Offline?
• Ray Tracing and Radiosity are inherently slow.
• Speedup possible by:– Brute-force: more hardware, multicore…
etc.– Approximate results
Under Simplified Assumption
• Can it become faster if:– …the view is fixed?– …the scene is static?– …the lights are simple?– …if indirect lighting is limited?
Lighting Design
• Assuming:– Static scene– Fixed (or limited) view
• Example:– Lpics: a hybrid hardware accelerated
relighting engine for computer cinematography, SIGGRAPH 2005
Lpics
Source: http://www.vidimce.org/publications/lpics/pdf/lpics-final-compressed.pdf
Instant Radiosity (and the Problem of Many Lights?)
• What if we place many virtual light sources to represent indirect lighting?
• How do we handle a very large number of light sources?– Lightcuts: A Scalable Approach to
Illumination, SIGGRAPH 2005
Reflective Shadow Maps• Dachsbacher and Stamminger. 2005 symposium on
Interactive 3D graphics and games (I3D '05).
Source: http://dl.acm.org/citation.cfm?doid=1053427.1053460
Precomputed Light Transport
Indirect Lighting
• Many indirect lighting effects are subtle, yet crucial for visual realism. Examples are:– Soft shadow– Ambient occlusion
Ambient Occlusion• Ambient light is a very crude
approximation to indirect reflections of surrounding objects.
• What if a point can’t see much of its surrounding?
From: Janne Kontkanen & Samuli LaineACM I3D 2005
Soft Shadow from Environment Lighting
Sloan, Kautz, Snyder 2002
Shadows from smooth lighting (precomputed radiance transfer)
Sen, Cammarano, Hanrahan, 2003
Shadows from point-lights(shadow maps, volumes)
Beyond Monte Carlo Path Tracing?
• Are global illumination solvers always time consuming?
• What if the scene and the lights are static ? Radiosity (view can changes!)
• What if only the scene is static?
Light Stage
• Take photos under single point light at various positions.
• Trivial questions: how to produce new images at:– Two point lights?– Area light?– Environment light (captured by light
probe)?
Precomputed Light Transport
• Three important papers to start with:– "Precomputed Radiance Transfer for Real-Time
Rendering in Dynamic, Low-Frequency Lighting Environments" Sloan et al., SIGGRAPH 2002
– "All-Frequency Shadows Using Non-linear Wavelet Lighting Approximation" Ng et al., SIGGRAPH 2003.
– "Triple Product Wavelet Integrals for All-Frequency Relighting" Ng et al. SIGGRAPH 2004
The following 8 slides are from Ren Ng’s SIGGRAPH 2003 presentation
Relighting as Matrix-Vector Multiply
1
2
3
N
P
P
P
P
11 12 11
21 22 22
31 32 3
1 2
M
M
M
NN N NM
T T TL
T T TL
T T T
LT T T
Relighting as Matrix-Vector Multiply
1
2
3
N
P
P
P
P
11 12 11
21 22 22
31 32 3
1 2
M
M
M
NN N NM
T T TL
T T TL
T T T
LT T T
• Input Lighting(Cubemap Vector)
• Output Image(Pixel Vector)
• TransportMatrix
Ray-Tracing Matrix Columns
11 12 1
21 22 2
31 32 3
1 2
M
M
M
N N NM
T T T
T T T
T T T
T T T
Ray-Tracing Matrix Columns
11 12 1
21 22 2
31 32 3
1 2
M
M
M
N N NM
T T T
T T T
T T T
T T T
11 12 1
21 22 2
31 32 3
1 2
M
M
M
N N NM
T T T
T T T
T T T
T T T
11 12 1
21 22 2
31 32 3
1 2
M
M
M
N N NM
T T T
T T T
T T T
T T T
Light-Transport Matrix Rows
11 12 1
21 22 2
31 32 3
1 2
M
M
M
N N NM
T T T
T T T
T T T
T T T
Light-Transport Matrix Rows
11 12 1
21 22 2
31 32 3
1 2
M
M
M
N N NM
T T T
T T T
T T T
T T T
Light-Transport Matrix Rows
11 12 1
21 22 2
31 32 3
1 2
M
M
M
N N NM
T T T
T T T
T T T
T T T
Rasterizing Matrix Rows
Pre-computing rows
• Rasterize visibility hemicubes with graphics hardware
• Read back pixels and weight by reflection function
Low-Frequency vs. All-Frequency
Teapot in Grace Cathedral