RAY TRACING

1
RAY TRACING
2
Ray tracing

• To determine the color of a given pixel
• Create a ray from the eye, through the pixel, and
  into the world Intersect the ray with all objects
  in the scene
• Determine the visible surface

3
Forward ray tracing

• Light rays can be traced from the light source to
  the eye point

4
reverse ray tracing

• Or from the eye point back to the light source
• More efficient and more practical

5
Inter-object reflections

• We could trace a ray off reflective surfaces and
  determine if they hit objects if they do we
  compute the lighting equations for the secondary
  ray and determine the contribution of this
  reflection at the first intersection

6
Refraction

• Transparent and translucent objects refract
  (bend) the light that passes through them. We
  could compute refracted rays and trace them as
  well.
• We can calculate the angle from the indices of
  refraction of the two materials which interface
  at the ray-object intersection.

7
Shadows

• Or we can take our first step toward a full ray
  tracing algorithm
• We could trace a shadow-ray from the point of
  intersection toward the light and determine if
  some other object blocks the light source.

8
Recursive ray tracing

• Full recursive ray tracing (as suggested by
  Whitted) does all of these at every intersection.

9
The good the bad

• Good
• Transparency
• Reflections
• Shadows
• Conceptually simple / pretty easy to write no
  clipping, no projections, no scan conversion
• Bad
• Intersection tests are expensive
• Intersection tests are expensive
• Intersection tests are expensive
• Typical framebuffer ? 1 million pixels
• Typical scene 1 million polygons