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CS 563 Advanced Topics in Computer Graphics The Wonderful World of Birds and Feathers

CS 563 Advanced Topics in Computer Graphics The Wonderful World of Birds and Feathers. by Brad Goodwin. Over-View. Introduction Feather structure Technique Using Bezier Curves Technique Using L-system. Introduction. Mimic the complexity of nature Two tasks

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CS 563 Advanced Topics in Computer Graphics The Wonderful World of Birds and Feathers

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  1. CS 563 Advanced Topics in Computer GraphicsThe Wonderful World of Birds and Feathers by Brad Goodwin

  2. Over-View • Introduction • Feather structure • Technique Using Bezier Curves • Technique Using L-system

  3. Introduction • Mimic the complexity of nature • Two tasks • Model and render an individual feather (covered in all techniques) • Growing Feathers on birds (covered only by L-systems)

  4. Feather Structure • Techniques use biological model to structure feather

  5. Feather Types Four main types: • Filoplume • Specialized • Contour • Flying • Plume • Barbs longer than rachis • Semiplume • Contour/plume

  6. First Technique • Only models a single feather • Bezier Curves • Parameters of Feather (biological) • Rendering

  7. Bezier Curves Simple Math • Four points • Two endpoints • Two control points • Two equations • One for Y and one for X • All controlled by time t • If you need more than that check out: • http://www.moshplant.com/direct-or/bezier/

  8. Defineing Bezier Curves Bezier for both Vanes with 5 control points Bezier for Rachis Define a single barb with four points P0, P3 on vane and rachis Random (v1,v2)(v3,v4) determine P1, P2 Parameters that affect barbs

  9. Parameters Nb Number of barbs for each vane (2000 in practice)

  10. Parameters Continued • Fpv – Use to vary the length of the barbs • So 0 is no change and 1 is the largest change

  11. Parameters Continued • Fb -Used to control v1, v2, v3, v4 for each barb • So affects P1, P2 scaling the distance from P0 to P3

  12. Boolean Parameters • Sv -T or F symmetry of vanes • Uf -T or F uniform barbs (same shape or dif) • Uc -T or F modify length for each barb • If T then Fpv isn’t modified for each barb • Is -(not boolean) allows the division of Rachis into two segments to create an irregular feather.

  13. Rendering • Non-photorealistic • No texture map • Just a stick figure • Photorealistic • Texture map • Set up with map for both sides • Two parameters s,t • S is 0 to 1 along the barb • T is 0 at base and 1 at top

  14. Samples

  15. L-System Technique • Individual and growing • Mesostructure including barbules • Modeling and Rendering with BTF (Bidirectional Texture Function)

  16. Remember • Techniques use biological model to structure feather

  17. Shape interface control Allows user a lot of control on the shape of the feather 1 -rachis; 2 -left and right barbs; 3 –texture; 4 -outline

  18. Curve Illustration O -Outline left and right b -Barb left and right r -Rachis All are controlled in the User interface

  19. L-System Model N – length of feather and density of Barbs ML and MR – Define lengths of left and right Barbs R(0) generates feather based on Rachis and barb curves P1 generates first segment of rachis and two barbs P2 generates left barb segment P3 generates right barb segment

  20. L-System Continued • This set up is modified to take into account variations in the feather • Example if a twig were to brush through the barbs • Little hooks called cilium that hold barbs • Good for fiying

  21. Final L-System • Random force Fe which if it exceeds threshold of FL or FR then the barb is rotated by some random degree theta

  22. BTF • BTF – Bidirectional Texture Function • 6 Dimensions • Viewing direction v • Lighting direction l at surface point (x, y)

  23. BTF - Continued • Set on X axis so only 5D but renders just as well in most cases • Considers Opacity and difuse and Specular Relflections • Allows for detail up close • Can model Oil film interference and iridescence

  24. An Entire Bird • Skeleton Structure

  25. Growing Positions • Tried just at poly-mesh vertices and looked bad • Used turk’s algorithm to divide polygons

  26. Growing Direction

  27. Interpolate the rest

  28. Adding Wing Feathers

  29. Growth Collision

  30. Recursive Collision Detection Rotates until no collision and moves along the edge to a connected vertex

  31. Questions???????

  32. References • Chen Y et al, "Modeling and rendering of realistic feathers ", Proc. ACM SIGGRAPH 2002 • Franco C.G. and Walter M., "Modeling and Rendering of Individual Feathers", Proc. SIBGRAPI 2002 • Franco C.G. and Walter M., "Modeling the Structure of Feathers", Proc. SIBGRAPI 2001 • http://www.moshplant.com/direct-or/bezier/ • http://www.geocities.com/cocoo_chen/

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