Fill in the Blanks.

Sushrut Pavanaskar

History

• Solid modeling (e.g. Solidworks, Catia, Pro-E..)• Use of NURBS, Trimmed – Extreme control– Well developed utilities

• HEAVY Complex models• Need math to compute– GPU: Dedicated Hardware

• Our research – evaluation parallelized

Blanks (Gaps/Cracks)

• NURBS model = many surfaces• GPU evaluation is parallel• Neighbors don’t know– So they don’t match!

• CRACKS• NOT acceptable– MUST be removed

Anticipated Work• Determination of cracks with IDs– Contours, external edges need not be filled

• Determination of edges, colors to be filled in• Actual computation of areas to fill• Filling in appropriate direction• Challenges– All this to be done on the GPU frag. Shader– No neighbor information available– No curvature information available– This has to be quick – does no value addition

Determination of a CRACK

• First pass over current view port for IDs• Reads and keeps ID_Tex on the GPU itself• “Cracks” seen clearly

Cracks and Neighborhood

• Cracks have nonmatching IDs• But could be anything Types• SurA – Bk – SurB– Not always a crack!

• SurA – SurX – SurB– SurX can be SurA/B

• Bk – SurA (Silhouette)– I need not care for them

Real Issue of “knowledge”

• Fragment shader knows nothing @ neighbors – Just knows about that fragment, and IDs of neigh

• Fragment shader (GPU) cant color anything– It can just permit rendering or not

• When rendering, no “knowledge” of surfaces– So no filling there

• GPU CPU data transfer takes time!– So SurfaceIDs available only to fragment shader

Anticipated work• Determination of cracks with IDs– Contours, external edges need not be filled

• Determination of edges, colors to be filled in• Actual computation of areas to fill• Filling in appropriate direction• Challenges– All this to be done on the GPU frag. Shader– No neighbor information available– No curvature information available– This has to be quick – does no value addition

Solution (as anticipated) - Edges

• Reading the edges– More technical challenge than geometrical– Read ACIS data structure– Loop through, enquire, read and store colors

• Coloring for OPENGL – readily done– kdcolor, kscolor, ka use with normals

• Sampled edge for 10 parametrically equidistant points, stored as “edge-points”

Triangle Strip Surrounding the Edge

• Can know exact properties of edge,– So draw edge quads, but render selectively

(Un)anticipated Work

• Model space Screen space– Wanted triangle strips on screen space– But edges in model space

• Use OPENGL transformation + view matrix– Invert, calculate quad dimensions, re-invert

• All drawing is done in model space

Dealing with Silhouette Edges

• Used out-normal of edge • Dot prod with view vector– Same sign => render– Diff sign => don’t

• Still a preliminary test– Sometimes “ab”-normals

Preliminary Result