Suggestive contours with geometry shader
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Suggestive Contours with Geometry Shader. Based on Suggestive Contours for Conveying Shape SIGGRAPH 2003. Sungbae Kim Master Student College of Computing Georgia Tech. Conveying shape with lines. Contours and Suggesstive Contours [DeCarlo et al. 2003]. Related work. Contour

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Suggestive Contours with Geometry Shader

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Suggestive contours with geometry shader

Suggestive Contours withGeometry Shader

Based on Suggestive Contours for Conveying ShapeSIGGRAPH 2003

Sungbae Kim

Master Student

College of Computing

Georgia Tech


Conveying shape with lines

Conveying shape with lines

Contours and Suggesstive Contours

[DeCarlo et al. 2003]


Related work

Related work

Contour

(also called silhouette)

Crease

Ridges and valleys

(also called crest)

Rusinkiewicz, SIGGRAPH 2005 Course note


Suggestive contours

Suggestive Contours

  • Contours have shape cue

  • Contours in nearby viewpoints also have shape cue

     Suggestive Contours

  • Contours + Suggestive Contours

q : contour

p : suggestive contour

Should appear suddenly

[DeCarlo et al. 2003]


How to find contours

How to find contours

  • Draw lines where N(P)∙V(P) = 0


How to find sc

How to find SC

  • Contours in nearby viewpoints

    local minima n∙v

    Kr = 0 && DwKr > 0

[DeCarlo et al. 2003]


How to find contours in mesh

How to find contours in mesh

  • Compute Per vertex

  • Draw zero crossing

Rusinkiewicz, SIGGRAPH 2005 Course note


How to compute kr 0 in mesh

Primary direction 1

Primary direction 2

w

How to compute Kr=0 in mesh

  • K1, K2 can be pre-computed per vertex

  • Compute Per vertex

  • Draw zero crossing

Kr > 0

Kr < 0

Kr < 0


How to compute dwkr 0 in mesh

How to compute DwKr > 0 in mesh

Rusinkiewicz, SIGGRAPH 2005 Course note

  • P, Q, S, T can be pre-computed per vertex

  • Compute Per vertex

  • Interpolation

Primary direction 1 : e1

Kr > 0

v

DwKr > 0

u

Kr=0

w

Primary direction 2 : e2

Kr < 0

Kr < 0


Implementation

Implementation

CPU - Intel Core2 Duo 2.0GHz, RAM - 2GB, VIDEO Card – NVIDIA Quadro FX 570M


Implementation challenges

Implementation Challenges

  • Calculation values from mesh

    • Primary directions

    • Primary curvatures

    • Derivatives of curvatures (P, Q, R, S)

      Use TriMesh library

  • Cg is very easy

  • Geometry shader


Geometry shader

Geometry Shader

  • Operation Per Primitives (line, triangle, line with adjacency, triangle with adjacency, etc.)

  • Generating new primitives such as line, triangle

  • Few references

  • Several examples from NVIDIA

triangle with adjacency

Draw edges between front and back face

My motivation

Example from NVIDIA OpenGL SDK 10


Using gpu

Using GPU

  • Pre-compute curvatures, dcurvatures in CPU when loading mesh

  • View-dependent calculation and line generation in Vertex & Geometry shader

    • Use texture coordinates as input arguments

  • Too many vertices, normals, faces, texture coordinates

    • Use buffer object


Remove hidden lines

Remove hidden lines

  • Using z-buf

  • 2-pass rendering

    • 1st pass : Setting depth values by Rendering mesh

    • 2nd pass : line drawing


Results

Results

vertices : 48484

triangles : 96964

51 fps

Horse


Results1

Results

vertices : 72027

triangles : 144046

34 fps

Bunny


Results2

Results

vertices : 262909

triangles : 525814

10 fps

Lucy


Results3

Results

vertices : 237018

triangles : 474048

3.5 fps

Angel


Results4

Results

vertices : 437645

triangles : 871414

6 fps

Dragon


Results5

Results

vertices : 543652

triangles : 1087116

4 fps

Happy Buddha


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