Geometry Image-based Shadow Volume Algorithm for Subdivision

Surfaces

Min Tang, Jin-Xiang DongCollege of Computer Science, Zhejiang University

{tang_m, djx}@zju.edu.cn

Contents

Related WorksRelated Works Main ContributionsMain Contributions Algorithm PipelineAlgorithm Pipeline EvaluationEvaluation Silhouette DetectionSilhouette Detection Implementation and Results Implementation and Results DemoDemo Conclusion & Future WorksConclusion & Future Works

Related Works

•Subdivision Surface Evaluation on GPU •GPU based shadow volume algorithm•Geometry Image

The work here is a extension of our previous work at CGI06:Real-time Shadow Volume Algorithm for Real-time Shadow Volume Algorithm for Subdivision Surface Based ModelsSubdivision Surface Based Models by Min Tang, et al.

Main Contributions

Improved efficiency:By using two geometry images to pack all the patches’ information, the efficiencies of silhouette detection and shadow volume generation are greatly improved (2 render-to-texture ops per model under dynamic lighting).

Improved accuracy:An enhanced silhouette detection method is designed to improve accuracy and ensure robustness

Algorithm Pipeline

Shadow Volume Extrusion on GPUScale by factor of 2x1

Control Meshes

Shadow Volume Image

Silhouette Image

Silhouettes Dectection on GPUScale by factor of 2x1

Two Global Geometry Images

Limit Positions

Normal Vectors

Evaluate on GPU

Subdivision Surfaces

Silhouettes

Shadow VolumeShadowed Scene

Evaluation

(a) Control meshes(b) Rendering using the two geometry images

(c) The geometry image storing normal vectors

(d) The geometry image storing limit positions

(a) Control meshes(b) Rendering using the two geometry images

Silhouette Detection

Directed visibility interpolation for silhouette extraction (+ for visible, - for invisible)

Silhouette Detection

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(a) Silhouette detection using normal vector of adjacent facets in [17]

(b) Silhouette detection using the directed visibility interpolation method

Silhouette Detection

Cracks caused by numeric instability [17]

Smooth linked silhouettes

Silhouette Detection

Cracks caused by numeric instability [17]

Smooth linked silhouettes

Silhouette Detection

Shadow leaks caused by the cracks [17]

Our result with the same light source

Silhouette Rendring

(a) a silhouette image (b) silhouettes

Shadow Volume Generation

Comparison with [17]

Render-to-TextureRender-to-Texture FPSFPS

Our methodOur method 11 ~75~75

[17][17] Num_of_Patches*3Num_of_Patches*3 ~15~15

Implementation and Results

(a) Shadows and silhouettes of the mode in Figure 1 (288 patches), ~75fps

(b) shadows and silhouettes of a face-shaped model (288 patches), ~75fps

(c) shadow and silhouettes of a complex model (480 patches), ~37fps

Demo&Source Code

http://www.cs.wichita.edu/~tang/SubShadow/subShadow.htm.

Conclusion & future works Extension to geometry imagesSpeed is limited by the RTVA efficiency

ThanksThanks ！！

Q&AQ&A