1. Ray Tracing
Dr. Scott Schaefer

2. Ray Tracing Provides rendering method with
Refraction/Transparent surfaces
Reflective surfaces
Shadows

3. Ray Tracing Provides rendering method with
Refraction/Transparent surfaces
Reflective surfaces
Shadows
Image taken from

4. Ray Tracing Provides rendering method with
Refraction/Transparent surfaces
Reflective surfaces
Shadows
Image taken from

5. Ray Tracing Provides rendering method with
Refraction/Transparent surfaces
Reflective surfaces
Shadows

6. Essential Information for Ray Tracing
Eye point
Screen position/orientation
Objects
Material properties
Reflection/Refraction coefficients
Index of refraction
Light sources

7. Recursive Ray Tracing For each pixel
Intersect ray from eye through pixel with all objects in scene
Find closest (positive) intersection to eye
Compute lighting at intersection point
Recur for reflected and refracted rays (if necessary)

8. screen
eye

9. screen
eye

10. screen
eye

11. normal
screen
eye

12. Ray Casting
Removes hidden surfaces
Per-pixel lighting computations

13. Shadows Cast a virtual ray to each light source
If ray hits an opaque object before the light, then omit contribution of that light
If ray hits a semi-transparent object, scale the contribution of that light and continue to look for intersections
Note: objects may be self-shadowing!!!

14. shadow ray
normal
screen
eye

15. Shadows

16. Shadows

17. normal
reflected ray
screen
eye

18. shadow ray
normal
reflected ray
normal
screen
eye

19. normal
reflected ray
reflected ray
normal
screen
eye

20. Reflection
Mirror-like/Shiny objects
Surface

21. refracted ray
normal
screen
eye

22. Refraction
Bending of light caused by different speeds of light in different medium
Each (semi-)transparent
object has an index of
refraction ci
Use Snell’s law to find
refracted vector
Image taken from

23. Snell’s Law
Surface

24. Snell’s Law
Surface

25. Snell’s Law
Surface

26. Snell’s Law
Surface

27. Snell’s Law
Surface

28. Snell’s Law
Surface

29. Snell’s Law
Surface

30. Snell’s Law
Surface

31. Snell’s Law
Surface

32. Snell’s Law
Surface

33. Total Internal Reflection
Surface

34. Recursive Ray Tracing
Truncate at finite depth!

35. Recursive Ray Tracing
Recur for reflective/transparent objects

36. Recursive Ray Tracing
Recur for reflective/transparent objects

37. Optimizations Lots of rays to cast!
Ray-Surface intersections are expensive
Associate with each object
Bounding box in 3-space
If ray doesn’t intersect box, then ray doesn’t intersect object

38. Parallel Processing Ray tracing is a trivially parallel algorithm!
Cast rays in parallel
Cast reflection, refraction, shadow rays in parallel
Calculate ray/surface intersections independently in parallel

39. Ray Tracing: Special Effects
copyright Newline Cinema

40. Ray Tracing: Video Games
These images are from a prototype computer game running in realtime on the ray tracer. It consists of more than 40 million polygons and all optical effects are fully simulated at rendering time. All trees are fully models and no LOD is being used.

41. Ray Tracing: Massive Models
Ray tracing has been the first and (to our knowledge) only technology to interactively render the entire Boeing 777 data set. It consists of 350 million polygons and takes up to 30 GB of data on disk. Every detail is models including tiny screws, cables, pipes, values, and many more. With ray tracing this model can be rendered interactively even on a dual-processor PC with 2-3 fps at video resolution.
The right image contains plants with a total of roughly 1.5 billion polygons. All leafs use alpha-mapped textures leading to an extremely high depth complexity. Still the scene can be rendered with interactive performance on a decent PC cluster. Even smooth lighting from the sky dome can be integrated. An good approximation is then shown during interaction but the image converges to a high quality solution with a few seconds.

42. Extensions of Ray Tracing
Only considers totally specular interactions
rays either reflect perfectly or refract perfectly
Ray traced scenes don't
show “color bleed”