1. Image

2. Examples

3. Examples

4. Ray Tracing
Ray tracing is a realistic method for rendering 3D computer graphics environments.
It works by tracing the path taken by a ray of light through the scene, and calculating reflection, refraction, or absorption of the ray whenever it intersects an object in the world.
Effects such as reflections and shadows, which are difficult to simulate in other algorithms, follow naturally from the ray tracing algorithm.

5. Ray Tracing
This method is very good at simulating specular reflections and transparency, since the rays that are traced through the scenes can be easily bounced at mirrors and refracted by transparent objects. The following scenes were generated with ray tracers developed at our institute.
Source:

6. Radiosity
Calculating the overall light propagation within a scene, for short global illumination is a very difficult problem. With a standard ray tracing algorithm, this is a very time consuming task, since a huge number of rays have to be shot. For this reason, the radiosity method was invented. The main idea of the method is to store illumination values on the surfaces of the objects, as the light is propagated starting at the light sources.

7. Ray Tracing

8. Classical Recursive Ray Tracing
For each pixel in image {
Create ray from eyepoint passing through this pixel
Initialize NearestT to INFINITY and NearestObject to NULL
For every object in scene {
If ray intersects this object {
If t of intersection is less than NearestT {
Set NearestT to t of the intersection
Set NearestObject to this object }

9. Classical Recursive Ray Tracing (Cnt.)
If NearestObject is NULL {
Fill this pixel with background color
} Else {
Shoot a ray to each light source to check if in shadow
If surface is reflective, generate reflection ray: recurse
If transparent, generate refraction ray: recurse
Use NearestObject and NearestT to compute shading function
Fill this pixel with color result of shading function }

10. The Basic Idea
This approach simulates light rays from light source to an observer's eye.
Observer
Light
Source
Reflected ray
Object

11. “Forward” Ray-Tracing
Trace rays from light
Lots of work for little return
Light
Image
Plane
Light Rays
Eye
Object
Source:

12. “Backward” Ray-Tracing
Trace rays from eye instead
Do work where it matters
Light
Image
Plane
Eye
Object
Source:

13. Ray Parametric form
Ray expressed as function of a single parameter (“t”)
<x, y, z> = <xo, yo, zo> + t * <xd, yd, zd>
<x, y, z> = ro + trd
t = 2.5
rd = <xd, yd, zd>
t = 2.0
t = 1.0
ro = <xo, yo, zo>
t = 0.0
Source:

14. Generating Rays Trace a ray for each pixel in the image plane Image
fovx
Eye
Eye
Source:

15. Generating Rays Trace a ray for each pixel in the image plane
Side View m
(tan(fovx)* 2) / m
(tan(fovy)* 2) / n
Eye n
Image
Plane
Source:

16. Triangle Intersection
Want to know: at what point (p) does ray intersect triangle?
Compute lighting, reflected rays, shadowing from that point p rd ro
<?, ?, ?>
(t = ???)
Source:

17. Lighting We’ll use triangles for lights Some lighting terms
Build complex shapes from triangles
Some lighting terms
Light
Eye N I R V
Surface
Source:

18. Lighting Use modified Phong lighting for each light
similar to OpenGL
simulates rough and shiny surfaces
for each light
In = IambientKambient +
IdiffuseKdiffuse (L.N) +
IspecularKspecular (R.V)n
Source:

19. Ambient Light Iambient Simulates the indirect lighting in a scene. Eye
Source:

20. Diffuse Light Idiffuse simulates direct lighting on a rough surface
Viewer independent
Paper, rough wood, brick, etc...
Eye
Light

21. Specular Light Ispecular simulates direct lighting on a smooth surface
Viewer dependent
Plastic, metal, polished wood, etc...
Eye
Light

22. Shadow Test Check against other objects to see if point is shadowed
Eye
Shadowing
Object

23. Reflection Angle of incidence = angle of reflection ( qI = qR )
I, R, N lie in the same plane
R = I - 2 (N . I) N N qI qR I R
Source:

24. This is A Good Start
Lighting, Shadows, Reflection are enough to make some compelling images
Want better lighting and objects
Need more speed

25. More Quality, More Speed
Better Lighting + Forward Tracing
Texture Mapping
Modeling Techniques
Motion Blur, Depth of Field, Blurry Reflection/Refraction
Distributed Ray-Tracing
Improving Image Quality
Acceleration Techniques

26. Reflections Reflections are generated using ray tracing.
In real life, the interaction of light with a
reflective object occurs in the following
sequence: a light source emits photons.
photons collide with and bounce off of
objects (some energy is absorbed by such
collisions, which is why we see color.)
photons travel into the eye.

27. Shadows Shadows are very simple to do in a
ray tracer. A point is in shadow if a
ray from that point to the light source
intersects an objects, then the Point
is in shadow. In order to apply diffuse
shading, the point of intersection of a
ray and a sphere has already been
calculated.
Source:

28. Ray Tracing Tools Professional Tool Free Tools
RenderMan is the name of a rendering software package developed by Pixar Animation Studios; it implements Pixar's photorealistic 3D description standard, the RenderMan Interface Specification.
Free Tools
POV-Ray
YafRay
BRL-CAD
OpenRT

29. Examples

30. Examples

31. Examples

32. Ray Tracing Paths Ra Tc D Rc C A Rb Ra Ta Ra B Ta A C B PRP Tc Rc Rb DRd