Real-Time, All-Frequency Shadows in Dynamic Scenes

Thomas Annen* Zhao Dong* Tom Mertens†

Philippe Bekaert† Hans-Peter Seidel* Jan Kautz‡

*MPI InformatikGermany

†Hasselt UniversitytUL - IBBT, EDM, Belgium

‡University College LondonUK

Some materials are get from the author and this paper is presented by CG, Huang

Outline• Introduction• Relate work• Convolution• Generation of Area Lights for Environment

Maps• Limitations• Result

Outline• Introduction• Relate work• Convolution• Generation of Area Lights for Environment

Maps• Limitations• Result

Introduction• Enable real-time, all-frequency shadows in

dynamic scenes.• Support area light as well as wnviroment

lighting.• The key contribution is renderng plausible soft

shadow.• Enviroment-lit scenes can be rendered.

Outline• Introduction• Relate work• Convolution• Generation of Area Lights for Environment

Maps• Limitations• Result

1. Soft Shadows2. Convolution3. Precomputation and Simplification4. Environment map sampling

Soft shadows• Early work on shadow mapping extensions

image-based rendering to average hard shadow.[Chen and Williams 93; Agrawala et al. 00]

• Classic shadow volumn method was extended to soft shadows.[Assarsson and Akenine-Moller 03]

Convolution• Soler and Sillion[98] propose an image-based

shadow algorithm based on convolution.• Don’t support self-shadowing.

• Variance shadow maps[Donnelly and Lauritzen 06]

• Convolution shadow maps[Annen et al. 07]

Precomputation and simplification• PRT [Sloan et al. 02] calculate and stroes an

illumination-invariant transport solution off-line and uses it for real-time relighting.• Challenging to support fully dynamic scenes with

arbitrary illumination.

Environment map sampling• Agarwal et al.[03] proposed an efficient point

sampling strategy for environment maps.• Arbree et al. Use disk-shaped light sources to

approximation.• This paper approximate an environment with

a collection of square light sources.

Outline• Introduction• Relate work• Convolution• Generation of Area Lights for Environment

Maps• Limitations• Result

c

L

Convolution shadow map• x R3

• p R2 • P = T(x)• Shadow function:s(x):=f(d(x),z(p))

• Binary result:– 1 if d(x)<=z(p)– 0 else

x

p

d(x)

z(p)

Shadow test function: s(x)• What kind of

function is s(x)?

• Heaviside Step Function: H(t)

Sha

dow

term

for x’c

L

x

p d(x’)z(p)

x’

• Approximate shadow test with Fourier series

Convolution shadow map

)(tH c1 +c2 +..+c4 +..+c8 +..+c16

Convolution shadow map

• Step function becomes sum of weighted sin()

• Series is separable!

)sin()cos()cos()sin()sin( zdzdzd

)(tH c1 +c2 +..+c4 +..+c8 +..+c16

Convolution• Bulid on convolution-based methods.• Simulate penumbrae by filtering shadows

depending on the configuration of blocker, receiver, and light source.

CSM order reduction• Annen et al[07] using a Fourier series to

construct the f, but it’s prone to some artifacts and shadows at contact points may too bright.

Outline• Introduction• Relate work• Convolution• Generation of Area Lights for Environment

Maps• Limitations• Result

Generation of Area Lights for Environment Maps

Outline• Introduction• Relate work• Convolution• Illumination with Soft Shadows• Limitations• Result

1. Ringing Suppression2. Textured light sources

Outline• Introduction• Relate work• Convolution• Generation of Area Lights for Environment

Maps• Limitations• Result• Conclusions and Future work

1. DirectX 102. Dual-Core AMD 2.2GHz3. NVIDIA GeForce 8800 GTX graphics card

Result

• Buddha scene with 70k face

MM: MipmapsSAT: Summed area table

Result

Result

• Performance of this paper and image quality depend on:– choice of prefilter– Number of area lights– Shadow map size

Result

• Demonstrate the effect of the sharpening function G().

Result

• Shows the influence of the number of light sources used for approximating the environment map.

Outline• Introduction• Relate work• Convolution• Generation of Area Lights for Environment Maps

• Limitations• Result• Conclusions and Future work

1. Based on convolution.2. Fast enough to render many area light sources simul- taneously.3. Provide plausible results, even though they are not

entirely physically correct.4. At future work, intend to explore the use area lights for

indirect illumination.