Real-time Indirect Lighting Using Clustering Visibility

Zhao, Tobias, Thorsten, Jan*

*University College London

Motivation Indirect lighting is Crucial for GI rendering.

Check following 2 video clips.

– Real-time performance for fully deformable/dynamic scene is open problem Visibility computation is still the key bottleneck.

– Approximate visibility for indirect lighting is quite reasonable from perception viewpoint.

– Practical indirect lighting rendering for real game/film development.

Video1Rui Wang et al. EGSR07

Video2Casten Dachsbacher et al. I3D06

state-of-the-art Methods based on hierarchical radiosity

Interactive rendering performance Moderate-sized scene

PRT-based methods

Require precomputation, Static/rigid dynamic scene.

[Casten et al. sig07] [Dong et al. pg07]

[Iwasaki et al. egsr07] [Wang et al. egsr07] [Liu et al. eg07]

State-of-the-art Image-based SH exponential

– Deformable, low-freq lighting (SH) and only diffuse interreflection Methods based on instant radiosity [Keller sig97]

– The left two only support static/semi-dynamic scene– Tobias’ method support fully deformable scene, VPL + ISM

[Sloan et al. pg07]

[Laine et al. egsr07] [Casten et al. I3d05,06] [Tobias et al. Submitted to sigasia08

Rethinking Instant radiosity methods

Direct Light

VPL

VPL

VPL

VPL

VPLVPL

VPL

VPL

VPL

Receiver Pixel

1000 VPLs Good quality

1000 VPLs equals to rendering 1000 SMs,Visibility computation becomes bottleneck!

Cornell box Can we utilize virtual arealights? How to fast approximate the visibility function of virtual area lights?

Key: Convolution Soft Shadow Map[SIG08]So, 1000 SMs 40 CSSMs!

Goal and Contributions Goals

– Real-time indirect lighting rendering for fully dynamic scenes. (Focus on indirect lighting)

Planned contribution – Novel: Separate visibility and shading computation of indirect

lighting. Approximate the indirect visibility by the cluster of VPLs Virtual

Area Light (VAL) Shading still based on VPLs keep the accuracy and all-freq

indirect lighting (Caustics)

– Delta: A simplified GPU-based k-means method for clustering VPLs in fully dynamic scene scheme (mesh animation).

Novel && practical clustering criteria for indirect lighting.

Our approach

Direct Light

VPL

VPL

VPL

VPL

VPLVPL

VPL

VPL

VPL

Cluster

Cluster

ClusterCluster

Receiver Pixel

Our algorithm steps:

Step 1: Render the scene by direct lighting and at the same time generate the VPLs.

Step 2: GPU-based clustering of VPLs VALs

Step 3: For each VAL, approximate the visibility function Based on convolution shadow map [Our SIG08 Paper]

Step 4: Per-pixel rendering: visibility based on VALs and shading based on all VPLs.

Intended Results selling points

– Real-time practical indirect lighting rendering for fully dynamic scene

– Novel Virtual Area Light (VAL) concept applied into indirect lighting.

– Our GPU-based clustering method is simple && practical, which can be applied in lots of graphics cases.

who might be interested?– Game/Film-tech developers

Example images

Validation

Side-by-side Comparison– Path tracing (ground truth)– Traditional instant radiosity methods (VPLs)

Perception experiment?

Major Steps project team

– Zhao, Tobias, Thorsten, Jan

Current status:– We have the code ready for step 1 and 4– We have verified the kernel part for step 2 and 3

Unknown: Good clustering criterion, need experiments

which supporting algorithms are needed?– Good k-means clustering criterion we want to get a

square area from a group of points.

required hardware– Powerful PC equipped with powerful GPU

Questions and suggestions?

Possible venue:– EG09, I3D09?

Any suggestions?

Gracious Thanks