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 - effective Contours and Suggesstive Contours [DeCarlo et al. 2003]

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

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 Draw lines where N(P)∙V(P) = 0

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

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 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 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 Using z-buf 2-pass rendering 1st pass : Setting depth values by Rendering mesh 2nd pass : line drawing

Results vertices : 48484 triangles : 96964 51 fps Horse

Results vertices : 72027 triangles : 144046 34 fps Bunny

Results vertices : 262909 triangles : 525814 10 fps Lucy

Results vertices : 237018 triangles : 474048 3.5 fps Angel

Results vertices : 437645 triangles : 871414 6 fps Dragon

Results vertices : 543652 triangles : 1087116 4 fps Happy Buddha