Quick-VDR: Interactive View-Dependent Rendering of Massive Models

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Quick-VDR Interactive View-Dependent Rendering
of Massive Models

• Sung-Eui Yoon
• Brian Salomon
• Russell Gayle
• Dinesh Manocha
• University of North Carolina at Chapel Hill
• http//gamma.cs.unc.edu/QVDR

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Goal

• Interactive display of complex and massive models
  at high image fidelity
• Models from CAD, scientific simulation, and
  scanning devices
• High primitive counts
• Irregular distribution of geometry

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CAD Model Power Plant
12 million triangles Irregular
distribution Large occluders
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Isosurface from Turbulence Simulation (LLNL)
100 million triangles High depth complexity Sma
ll occluders Many holes
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Scanned Model St. Matthew
372 million triangles Highly tessellated
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Problems of current representation

• High cost of refining and rendering the geometry
• High memory footprint
• Complicate integration with other techniques
• occlusion culling and out-of-core management

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Main Contribution

• New view-dependent rendering algorithm

Clustered Hierarchy of Progressive Meshes (CHPM)
Out-of-core construction and rendering
Integrating occlusion culling and out-of-core
management
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Realtime Captured Video Power plant
Pentium IV GeForce FX 6800 Ultra 1 Pixel of Error
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Previous Work

• Geometric simplification
• View-dependent simplification
• Out-of-core simplification
• Occlusion culling
• Hybrid algorithms

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Geometric Simplification

• Static Cohen et al. 96 and Erikson et al. 01
• View-dependent Hoppe 97 Luebke et al. 97 Xia
  and Varshney 97
• Surveyed in Level of Detail book Luebke el al.
  02

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View-Dependent Simplification

• Progressive mesh Hop96
• Merge tree Xia and Varshney 97
• View-dependent refinement of progressive meshes
  Hoppe 97
• Octree-based vertex clustering Luebke and
  Erikson 97
• View-dependent tree El-Sana and Varshney 99
• Out-of-core approaches Decoro and Pajarola 02
  Lindstrom 03

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Out-of-core Simplification

• Static Lindstrom and Silva 01 Shaffer and
  Garland 01 Cignoni et al. 03
• Dynamic Hoppe 98 Prince 00 El-Sana and Chiang
  00 Lindstrom 03

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Occlusion Culling

• A recent survey is in Cohen-Or et al. 03
• Image-based occlusion representation
• Greene et al 93, Zhang et al, 97, Klosowski and
  Silva 01
• Additional graphics processors
• Wonka et al. 01, Govindaraju et al. 03

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Hybrid Approaches

• Combine model simplification and occlusion
  culling techniques
• UC Berkeley Walkthrough Funkhouser 96
• UNC MMR system Aliaga 99
• Integrate occlusion culling with view dependent
  rendering
• El-Sana et al. 01 Yoon et al. 03

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Outline

• CHPM representation
• Building a CHPM
• Interactive display
• Implementation and results
• Conclusion and future work

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Outline

• CHPM representation
• Building a CHPM
• Interactive display
• Implementation and results
• Conclusion and future work

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Clustered Hierarchy of Progressive Meshes (CHPM)

• Novel view-dependent representation
• Cluster hierarchy
• Progressive meshes

PM3
PM1
PM2
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Clustered Hierarchy of Progressive Meshes (CHPM)

• Cluster hierarchy
• Clusters are spatially localized mesh regions
• Used for visibility computations and out-of-core
  rendering

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Clustered Hierarchy of Progressive Meshes (CHPM)

• Progressive mesh (PM) Hoppe 96
• Each cluster contains a PM as an LOD
  representation

Vertex splits
PM
Base mesh
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Two-Levels of Refinement

• Coarse-grained view-dependent refinement
• Provided by selecting a front in the cluster
  hierarchy

Front
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Two-Levels of Refinement

• Coarse-grained view-dependent refinement
• Provided by selecting a front in the cluster
  hierarchy

Cluster-split
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Two-Levels of Refinement

• Coarse-grained view-dependent refinement
• Provided by selecting a front in the cluster
  hierarchy

Cluster-split
Cluster-collapse
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Two-Levels of Refinement

• Fine-grained local refinement
• Supported by performing vertex splits in PMs

PM
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Simplification Error Bound

• Conservatively compute object space error bound
  given screen space error bound
• Perform two-levels of refinement based on the
  error bound

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Main Properties of CHPM

• Low refinement cost
• 1 or 2 order of magnitude lower than a vertex
  hierarchy
• Alleviates visual popping artifacts
• Provides smooth transition between different LODs

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Video Comparison CHPM with Vertex Hierarchy
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Outline

• CHPM representation
• Building a CHPM
• Interactive display
• Implementation and results
• Conclusion and future work

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Overview of Building a CHPM
Input model
Cluster decomposition
Performed in out-of-core manner
Cluster hierarchy generation
Hierarchical simplification
CHPM
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Overview of Building a CHPM
Input model
Cluster decomposition
Cluster hierarchy generation
Hierarchical simplification
CHPM
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Cluster Decomposition

• Cluster
• Main unit for view-dependent refinement,
  occlusion culling, out-of-core management
• Spatially localized portion of the mesh
• Equally sized in terms of number of triangles

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Cluster Decomposition

• Similar to Ho et al. 01 Isenburg and Gumhold 03

Graph between cells
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An Example of Cluster Decomposition
Each cluster contains 4K triangles
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Overview of Building a CHPM
Input model
Cluster decomposition
Cluster hierarchy generation
Hierarchical simplification
CHPM
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Cluster Hierarchy Generation - Properties

1. Nearly equal cluster size
2. High spatial locality
3. Minimum shared vertices
4. Balanced cluster hierarchy

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Cluster Hierarchy Generation - Algorithm

• Node
• Corresponds to a cluster
• Weighted by the number of vertices
• Edge
• Made if clusters share vertices
• Weighted by the number of shared vertices

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Cluster Hierarchy Generation - Algorithm
2nd level clusters
Root cluster
3rd level clusters
Leaf clusters
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Overview of Building a CHPM
Input model
Cluster decomposition
Cluster hierarchy generation
Hierarchical simplification
CHPM
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Out-of-core Hierarchical Simplification

• Simplifies clusters in a bottom-up manner

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Out-of-core Hierarchical Simplification

• Simplifies clusters in a bottom-up manner

PM5
PM4
PM1
PM2
PM3
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Boundary Simplification
Boundary constraints
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Boundary Simplification
E
F
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Boundary Constraints

• Common problem in many hierarchical
  simplification
• Hoppe 98 Prince 00 Govindaraju et al. 03
• Degrades the quality of simplification
• Decrease rendering performance at runtime
• Aggravated as a depth of hierarchy increases

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Boundary Constraints
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Boundary Constraints
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Cluster Dependencies

• Replaces preprocessing constraints by runtime
  dependencies

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Cluster Dependencies
dependency
E
F
C
B
A
D
Cluster hierarchy
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Cluster Dependencies
dependency
E
F
C
B
A
D
Cluster hierarchy
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Cluster Dependencies at Runtime
Force cluster-split
Cluster-split
dependency
E
F
C
B
A
D
Cluster hierarchy
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Cluster Dependencies
92 triangles reduced
227K triangles
19K triangles
After posing cluster dependencies
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Outline

• CHPM representation
• Building a CHPM
• Interactive display
• Implementation and results
• Conclusion and future work

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View-Dependent Refinement
Traverse and update previous active cluster list
Active Cluster List (ACL)
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View-Dependent Refinement
cluster-split
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View-Dependent Refinement
cluster-collapse
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View-Dependent Refinement
The PM contained within acluster is refined
prior torendering
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Occlusion Culling

• Exploit temporal coherence
• Use visible clusters from the previous frame as
  potentially visible set (PVS) in the current
  frame
• Cluster bounding boxes tested using occlusion
  queries

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Rendering Algorithm
Traverse the ACL and apply split and
collapseoperations
1. Refine Active ClusterList
PVS is rendered. The depth map is the occlusion
representation
2. Render PVS as anoccluder set
Test boxes of clusterson ACL using occlusion
queries
3. Compute new PVS and newly visible set
Rendering newly visible set completes the final
image
4. Render newly visible set
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Out-of-core Rendering

• Entire hierarchy stored in memory
• Takes 5MB in St. Matthew model
• PMs stored on disk

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Out-of-core Rendering

• Fetch PMs as necessary
• Buffer for LOD Changes
• Latency for visibility events
• PMs replaced using LRU policy

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LOD Prefetching
Not Visible
Visible
LOD Prefetched
Front
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Visibility Prefetching

• Occlusion events are difficult to predict
• We use a frame of latency to reduce stalling
• The rendering algorithm is reordered using a pair
  of offscreen buffers

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Latency
Frame i1
Frame i
1. Refine ActiveCluster List
1. Refine ActiveCluster List
2. Render PVS as anoccluder set
2. Render PVS as anoccluder set
3. Compute new PVSand newly visible set
3. Compute new PVSand newly visible set
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Outline

• CHPM representation
• Building a CHPM
• Interactive display
• Implementation and results
• Conclusion and future work

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Implementation

• Use GL_ARB_vertex_buffer_object to manage PM data
  in GPU memory
• 5 of PMs change refinement level
• Implemented on Windows XP
• Uses virtual memory through memory mapped files
  Lindstrom and Pascucci 02

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Live Demo Isosurface

• Alienware laptop
• 3.2GHz Pentium IV PC with 2GB main memory
• Quadro FX Go5700 with 128MB GPU memory

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Live Demo St. Matthew

• Alienware laptop
• 3.2GHz Pentium IV PC with 2GB main memory
• Quadro FX Go5700 with 128MB GPU memory

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Test Configuration

• Dell Precision Workstations
• Dual 3.2 GHz Pentium IV PC with 1 GB main memory
• GeForce FX 6800 Ultra with 128MB of video memory

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Processing Time and Storage Requirement
Processing 30M triangles per an hour
Model Triangles (M) Memory footprint used (MB) Processing Time (hour)
Power plant 12.8 32 0.5
Isosurface 100 256 2.8
St. Matthew 372 512 10.2
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Processing Time and Storage Requirement

• CHPM requires 88MB per million vertices
• Low compared to 224MB (Hoppes VDPM) and 108MB
  (XFastMesh)
• Compression on PMs can further improve the memory
  overhead and storage overhead

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Runtime Performance
Model Pixels of error Frame rate Memory footprint Avg Tris
Power plant 1 28 400MB 542K
Isosurface 20 27 600MB 819K
St. Matthew 1 29 600MB 850K
Image resolution is 512 512
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Timing Breakdown
Model Rendering Occlusion Culling Refinement
Power plant 86 13 1
Isosurface 94 5 1
St. Matthew 94 4 2
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Refinement Comparison
1M Triangle Isosurface
Method Num Dependency Checks Total Refinement Time
Vertex Hierarchy 4.2M 1,065 msec
CHPM 223 28 msec
38X speedup
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Frame Rate - Isosurface
2X speedup
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Limitations

• Latency
• Reduces stalls but no guarantee
• Excludes latency-sensitive applications
• Requires high temporal coherence

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Advantages

• Refinement time
• Performance comparable to static LOD systems
• Combines out-of-core, VDR, and occlusion culling
• General
• CAD, scanned, isosurface models

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Conclusion

• Quick-VDR view-dependent rendering of massive
  models
• Generates crack-free and drastic high quality
  simplification by cluster dependencies
• Provides two levels of refinement using CHPM
• Applies to a wide variety of massive models

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Ongoing and Future Work

• Compression
• Consider dynamic effects
• Shadows
• Lighting
• Occlusion event prediction

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Application to Collision Detection

• Fast Collision Detection Between Massive Models
  Using Dynamic Simplification
• Presented in Symposium of Geometric Processing,
  2004

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Acknowledgements

• Anonymous donor for power plant model
• LLNL ASCI VIEWS for isosurface model
• Digital Michelangelo Project at Stanford
  University for the St. Matthew model

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Acknowledgements

• DARPA
• Army Research Office
• Intel Corporation
• Office of Naval Research
• National Science Foundation

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Acknowledgements

• Naga Govindaraju
• Martin Isenburg
• Stefan Gumhold
• Mark Duchaineau
• Peter Lindstrom
• Members of Walkthru group

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Questions?
Project URL http//gamma.cs.unc.edu/QVDR
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Quick-VDR Interactive View-Dependent Rendering
of Massive Models

• Sung-Eui Yoon
• Brian Salomon
• Russell Gayle
• Dinesh Manocha
• University of North Carolina at Chapel Hill
• http//gamma.cs.unc.edu/QVDR

83
Realtime Captured Video ST. Matthew
Pentium IV GeForce FX 6800 Ultra 1 Pixel of Error
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Comparison with TetraPuzzles
TetraPuzzles Quick-VDR
Representation Hierarchies of tetrahedron, close to static LOD CHPM, close to VDR
Handling boundary constraints (implicit) dependencies Using cluster dependencies
Models scanned models Wide variety of models
Occlusion culling Hasnt been tested Yes
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Live Demo Power plant

• Alienware laptop
• 3.2GHz Pentium IV PC with 2GB main memory
• Quadro FX Go5700 with 128MB GPU memory