Realtime Ray Tracing and Interactive Global Illumination - Scientific ...

12 Chapter 2: An Introduction to Ray Tracing
Camera
Point
light
source
Point
light
source
Camera
Point
light
source
Point
light
source
Glass Object
(reflective & refractive)
Glass Object
(reflective & refractive)
a.)
b.)
Camera
Point
light
source
Point
light
source
Camera
Point
light
source
Point
light
source
Glass Object
(reflective & refractive)
Glass Object
(reflective & refractive)
c.)
d.)
Figure 2.2: Recursive (whitted-style) ray tracing in a simple scene consisting
of a camera, some diffuse geometry, a partially specular glass object, and
two point light sources (a): A primary ray from the camera hits an object.
While “shading” that ray, shadow rays are sent towards the two light source
to determine their visibility (b). In order to compute reflection off the glass,
a secondary ray is recursively traced into the reflection direction to compute
the amount of incoming light. To do this, it can cast new shadow rays, or – if
necessary – additional reflection or refraction rays (c). After having finished
the reflection ray, the glass shader also computes the refraction direction, and
recursively casts a refraction ray (d).
usually goverened by well-known physical formulae), recursively tracing this
ray, and taking into account how much of this incoming light is actually
reflected into the direction of the incoming ray. By successively performing
these operations for each pixel in the virtual image plane, eventually the color
of all the pixels are computed, and the rendered image can be displayed.
In this recursive form, ray tracing has first been used by Turner Whitted
[Whitted80] in 1980. Therefore, it is often termed “whitted-style” ray
tracing, or “recursive” ray tracing 7 . It is this recursive application of ray
tracing that is most commonly used, and what most people associate with
the term “ray tracing”.
7 Other popular names for whitted-style ray tracing are “classical” ray tracing, or “fullfeatured
ray tracing”.