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