1. Suggestive Contours with Geometry Shader
Based on Suggestive Contours for Conveying Shape SIGGRAPH 2003
Sungbae Kim
Master Student
College of Computing
Georgia Tech

2. Conveying shape with lines
- effective
Contours and Suggesstive Contours
[DeCarlo et al. 2003]

3. Related work Contour (also called silhouette) Crease
Contour : lack of information
Crease : well for polyhedral objects
Crest : lack of view dependent nature that hand-drawn pictures possess
Contour
(also called silhouette)
Crease
Ridges and valleys
(also called crest)
Rusinkiewicz, SIGGRAPH 2005 Course note

4. 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]

5. How to find contours
Draw lines where N(P)∙V(P) = 0

6. How to find SC Contours in nearby viewpoints local minima n∙v
Kr = 0 && DwKr > 0
[DeCarlo et al. 2003]

7. How to find contours in mesh
Compute Per vertex
Draw zero crossing
Rusinkiewicz, SIGGRAPH 2005 Course note

8. How to compute Kr=0 in mesh
Primary direction 1
Primary direction 2 w
K1, K2 can be pre-computed per vertex
Compute Per vertex
Draw zero crossing
Kr > 0
Kr < 0
Kr < 0

9. 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

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

11. 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

12. 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

13. 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

14. Remove hidden lines Using z-buf 2-pass rendering
1st pass : Setting depth values by Rendering mesh
2nd pass : line drawing

15. Results
vertices : 48484
triangles : 96964
51 fps
Horse

16. Results
vertices : 72027
triangles :
34 fps
Bunny

17. Results
vertices :
triangles :
10 fps
Lucy

18. Results
vertices :
triangles :
3.5 fps
Angel

19. Results
vertices :
triangles :
6 fps
Dragon

20. Results
vertices :
triangles :
4 fps
Happy Buddha