Past Midterm and Exam Questions (PDF) - Student.cs.uwaterloo.ca ...

CS488/688 Introduction to Computer Graphics 45
15.16 Illumination [Last Used: Winter 2011 Final]
A unit sphere sits at the origin. Assume that we are using the following Phong illumination model:
(
L out (⃗v) = k a I a + k d max(0, ⃗n · ⃗l) + k s max(0, ⃗r · ⃗v) p) I
Here, I is the illumination power of a single light source after attenuation, and I a is a separate
ambient illumination level.
(a) Assume k a = k d = 1, k s = 0, and the light source is a point light source located at (x, y, z)
with x 2 + y 2 + z 2 > 1. What point on the sphere will be illuminated most brightly?
(b) If more than one of k d , k s and k a are nonzero, then it becomes possible for some primary rays
to yield pixels with intensities that are larger than the maximum intensity displayable on the
output devi ce. Briefly describe two methods for dealing with output values that are outside
the legal range.
(c) Assume k a = 0, k d > 0, and k s > 0. A directional light point s in the direction (0, 0, −1).
What range of z values on the sphere will be illuminated by the directional light?
(d) Now assume that the lighting and material properties are as in (c), but the directional light
is replaced by a point light a t (0, 0, 4). Will the same range of z values be illuminated by the
light? Explain why or why not, possibly using a diagram.
16 Radiosity
16.1 Radiosity vs. Ray Tracing [Last Used: Spring 1996 Final]
1. In radiosity, what does a form factor represent?
2. Both ray tracing and radiosity are global illumination models. Explain why radiosity is a
better method than ray tracing for computing global illumination for an architectural walkthrough.
16.2 Radiosity Solution Techniques [Last Used: Fall 2000 Final]
In radiosity, briefly describe the full matrix solution and the progressive refinement solution, noting
the differences between the two methods. Why might you prefer to use one method instead of the
other?
16.3 Hemi-cube [Last Used: Winter 1995 Final]
1. Describe the hemi-cube algorithm for estimating form factors.
2. What advantages are there to using a hemi-cube algorithm? Be sure to consider ways to
implement it and effects it can achieve.