Interactive Shadow Generation in Complex Environments Naga K. Govindaraju, Brandon Lloyd, Sung-Eui Yoon, Avneesh Sud, Dinesh Manocha Speaker: Alvin Date:

Interactive Shadow Interactive Shadow Generation in Complex Generation in Complex

EnvironmentsEnvironments

Naga K. Govindaraju, Brandon Lloyd, Naga K. Govindaraju, Brandon Lloyd,

Sung-Eui Yoon, Avneesh Sud, Dinesh Sung-Eui Yoon, Avneesh Sud, Dinesh ManochaManocha

Speaker: AlvinSpeaker: Alvin

Date: 2003/7/2Date: 2003/7/2

SIGGRAPH 2003SIGGRAPH 2003

Alivn/GAME LAB/CSIE/NDHU

2Interactive Shadow Generation in Complex Environments

OutlineOutline

IntroductionIntroduction LOD-based Interactive PVS LOD-based Interactive PVS

ComputationComputation Hybrid Shadow Generation Hybrid Shadow Generation

AlgorithmAlgorithm ResultResult ConclusionConclusion



IntroductionIntroduction Produce Produce hard-edgedhard-edged shadow. shadow. A hybrid approach.A hybrid approach.

The efficiencies of image-precision techniques. (The efficiencies of image-precision techniques. (Shadow Shadow MapMap))

The image quality of object-space methods. (The image quality of object-space methods. (Shadow Shadow VolumeVolume))

A interactive algorithm based on LOD and VC to A interactive algorithm based on LOD and VC to compute PVS.compute PVS.

A novel A novel cross-visibility cullingcross-visibility culling algorithm. algorithm. LOD-selection that avoid the artifacts in self-LOD-selection that avoid the artifacts in self-

shadow.shadow. In a three PC system.In a three PC system.



OutlineOutline






LOD-based Interactive PVS LOD-based Interactive PVS ComputationComputation

Key WordsKey Words Scene Graph RepresentationScene Graph Representation Occlusion CullingOcclusion Culling ProblemsProblems



Key WordsKey Words

PVS – PVS – PPotentially otentially VVisible isible SSet.et. PVSPVSEE – The – The PVS PVS from the from the eeye-view.ye-view.

PVSPVSLL – The – The PVSPVS from the from the llight-view.ight-view. HLOD – HLOD – HHierarchical ierarchical LLevels-evels-OOf-f-

DDetail.etail.



Scene Graph Scene Graph RepresentationRepresentation

Each node Each node stores stores references to references to its children its children and to its and to its bounding box.bounding box.



Occlusion CullingOcclusion Culling

Computing Occlusion Representation Computing Occlusion Representation (OR)(OR) Render the PVS from the previous frame Render the PVS from the previous frame

but based on the current camera location.but based on the current camera location. Generate a depth map.Generate a depth map.

Scene Graph Culling (SGC)Scene Graph Culling (SGC)Given the OR to use OQ.Given the OR to use OQ. Object Culling – LOD selection.Object Culling – LOD selection. Sub-object Culling – Visible sub-object at Sub-object Culling – Visible sub-object at

the leaf node are added to PVS.the leaf node are added to PVS.



ProblemsProblems

Inaccuracy in Shadow BoundariesInaccuracy in Shadow Boundaries When the distance between a shadow-caster When the distance between a shadow-caster

and a shadow-receiver is increased.and a shadow-receiver is increased. When the angle between the shadow-When the angle between the shadow-

receiver’s normal and the light source receiver’s normal and the light source direction almost 90direction almost 90o o ..

Self-ShadowsSelf-Shadows Ensure that LODEnsure that LODLL is the same as LOD is the same as LODEE for for

objects visible in both the views.objects visible in both the views.



ProblemsProblems

Recomputing PVSLRecomputing PVSL When the user move, LODE can When the user move, LODE can

change.change. Need to compute PVSL to avoid Need to compute PVSL to avoid

self-shadows and popping in the self-shadows and popping in the final image.final image.



OutlineOutline






Hybrid Shadow Generation Hybrid Shadow Generation AlgorithmAlgorithm

Cross CullingCross Culling Shadow GenerationShadow Generation Architecture of The Process-Parallel Architecture of The Process-Parallel

Algorithm.Algorithm. Frame WorkFrame Work



Cross CullingCross Culling

Partitions the PVSPartitions the PVSEE into three subsets. into three subsets. Fully-lighted (FV)Fully-lighted (FV) Fully-shadowed receivers (SRFully-shadowed receivers (SRFF)) Partially-shadowed receivers (SRPartially-shadowed receivers (SRPP))

Proceeds in two step.Proceeds in two step. Based on OQ, partitions PVSBased on OQ, partitions PVSEE into FV, SR into FV, SRFF, ,

SRSRPP.. Cull away those in PVSCull away those in PVSLL but do not cast a but do not cast a

shadow on SRshadow on SRPP. The remaining, SC, are used . The remaining, SC, are used for shadow generation.for shadow generation.



Shadow GenerationShadow Generation

SRSRPP are clipped against the shadow are clipped against the shadow frusta formed by SC.frusta formed by SC.

The resulting shadow-polygons are The resulting shadow-polygons are calculated by repeatedly clipping the calculated by repeatedly clipping the scene triangles against the planes of scene triangles against the planes of the shadow frusta.the shadow frusta.



RenderingRendering

The shadow are rendered in two The shadow are rendered in two passes:passes: SRSRFF and SR and SRPP are rendered with only are rendered with only

ambient lighting. The shadowed ambient lighting. The shadowed polygons are rendered to the stencil polygons are rendered to the stencil buffer with the depth test enabled.buffer with the depth test enabled.

SRSRPP and FV are rendered with full and FV are rendered with full lighting using the stencil test to prevent lighting using the stencil test to prevent writing in the shadowed regions.writing in the shadowed regions.



Architecture of The Architecture of The Process-Parallel AlgorithmProcess-Parallel Algorithm



Frame WorkFrame Work



OutlineOutline






ResultResult

Experiment EnvironmentExperiment Environment PerformancePerformance SnapshotSnapshot DemoDemo



Experiment EnvironmentExperiment Environment

On 3 Dell Precision workstations.On 3 Dell Precision workstations. With dual 1.8 GHz pentium CPUsWith dual 1.8 GHz pentium CPUs 2 GB of main memory2 GB of main memory A NVIDIA GeForce-4 Ti 4600 GPUA NVIDIA GeForce-4 Ti 4600 GPU Allocate 72MB out of 128MB on each Allocate 72MB out of 128MB on each

GPU to store the vertices of objects, GPU to store the vertices of objects, sub-objects, and bounding boxes.sub-objects, and bounding boxes.

Use Vertex Arrays and OQ.Use Vertex Arrays and OQ.



PerformancePerformance



SnapshotSnapshot



SnapshotSnapshot



SnapshotSnapshot



SnapshotSnapshot



DemoDemo



OutlineOutline






ConclusionConclusion

Generate hard-edge shadow.Generate hard-edge shadow. Reduce the aliasing artifact that are Reduce the aliasing artifact that are

present in pure image-precision present in pure image-precision approaches.approaches.

Present an improved algorithm for Present an improved algorithm for PVS computation.PVS computation.

The Cross-culling algorithm can The Cross-culling algorithm can accelerate the performance of a pure accelerate the performance of a pure shadow volume approachshadow volume approach



Thanks for your

attention!

Interactive Shadow Generation in Complex Environments Naga K. Govindaraju, Brandon Lloyd, Sung-Eui Yoon, Avneesh Sud, Dinesh Manocha Speaker: Alvin Date:

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