1. CSE 872 Dr. Charles B. Owen Advanced Computer Graphics1 Ray Tracing Variants Distributed ray tracing Generalized rays Cone Tracing Beam Tracing Pencil Tracing Constructive solid geometry Acceleration methods

2. CSE 872 Dr. Charles B. Owen Advanced Computer Graphics2 Distributed Ray Tracing General term for “shoot a bunch-o-extra rays” Solution for “fuzzy” phenomena

3. CSE 872 Dr. Charles B. Owen Advanced Computer Graphics3 Examples Distributing reflected rays according to specular distribution function (blurry reflection) Distributing transmitted rays (blurry transparency) Distributing shadow feelers (penumbra) Distributing ray origins over camera lens (depth of field) Distributing rays in time (motion blur)

4. CSE 872 Dr. Charles B. Owen Advanced Computer Graphics4 What’s the matter with ray tracing? ?

5. CSE 872 Dr. Charles B. Owen Advanced Computer Graphics5 What’s the matter with ray tracing? Infinitesimally small rays are point sampling our space We generally fix this using more rays – Contributes to exponential blowups We don’t take advantage of coherence

6. CSE 872 Dr. Charles B. Owen Advanced Computer Graphics6 Generalized Rays Rays that have a shape of some kind – Cone for example Why?

7. CSE 872 Dr. Charles B. Owen Advanced Computer Graphics7 Cone Tracing Apex Spread angle Center line

8. CSE 872 Dr. Charles B. Owen Advanced Computer Graphics8 Partial Intersections What do we do?

9. CSE 872 Dr. Charles B. Owen Advanced Computer Graphics9 Cone tracing Intersection test is more complicated Complex surface geometry is very difficult How do we do: – Reflections? – Shadow feelers?

10. CSE 872 Dr. Charles B. Owen Advanced Computer Graphics10 Beam Tracing Rays with polygonal cross sections

11. CSE 872 Dr. Charles B. Owen Advanced Computer Graphics11 How arbitrary are the cross sections? Non-convex? Holes? How big should initial beam be?

12. CSE 872 Dr. Charles B. Owen Advanced Computer Graphics12 How to? Shadows Penumbra Reflections

13. CSE 872 Dr. Charles B. Owen Advanced Computer Graphics13 Beam Trees Each beam can generate additional beams due to: – Continuing past object – Splitting around object – Shadow feelers – Reflections These form a tree

14. CSE 872 Dr. Charles B. Owen Advanced Computer Graphics14 Beam Tracing Big Advantage Takes advantage of spatial coherence!

15. CSE 872 Dr. Charles B. Owen Advanced Computer Graphics15 Pencil Tracing Pencil – Centered axial ray – Set of paraxial rays Closely aligned to axial ray Infinite set (not actually represented) – Uses paraxial theory of optics Optics can be approximated using linear transformations “in the small” 4 x 4 transformation matrix for each pencil intersection, concatenate matrices

16. CSE 872 Dr. Charles B. Owen Advanced Computer Graphics16 A fast ray tracer using pencil tracing Use rays around the edges and pencils in large (multiple pixel) shaded areas Order of magnitude improvement Approximation, though.

17. CSE 872 Dr. Charles B. Owen Advanced Computer Graphics17 Constructive Solid Geometry Ray tracing is very natural for CSG How?

18. CSE 872 Dr. Charles B. Owen Advanced Computer Graphics18 Ray Tracing Acceleration Techniques Acceleration Techniques Faster Intersections Fewer RaysGeneralized Rays Fewer ray-object intersections Faster ray-object intersections Bounding volumes Efficient surfaces Volume hierarchies Spatial subdivision Directional techniques Adaptive tree-depth Adaptive sampling Beam tracing Cone tracing Pencil tracing