EECS 487 Fall 2008 Homework - 3
Due 03 Nov 2008
1 OpenGL Lighting Model (25 pts)
You are an intelligene agent who has to ommuniate a seret ode to another agent on the eld.
You deide to do this in an abstrat art museum by sribbling a ode on a painting and making
it seletively visible to the eld-agent
1
. The painting you hoose is a 3-ft-by-6-ft square painted
uniformly with only one olor and the ink onforms to an OpenGL material with diuse olor
1
2,1
4,1
4
and is titled
CitiZen
2
. It is lit with a diretional light of OpenGL olor
(1,1,1)
at an angle
300
from the vertial, from the eiling. During exhibit hours, the museum runs a white fog in the
room (for surrealism) suh that a person at a distane
d
feet from the enter of the painting sees
only a fration
1
1+ 1
2d
of the olor from the painting and the rest, white from the ambient fog. To
take advantage of the white fog you deide that the ode should appear in white to the eld-agent so
that others not atively looking for it may dismiss it as an illusion from the fog should they see it by
aident. You sneak up the previous night and sribble the ode on the painting at a height of 2.5 ft
knowing that the eld-agent is 5-ft. tall. You write the ode with magi ink whih onforms to an
OpenGL material with diuse olor
1
2,1
4,1
4
and speular olor
3
4,7
8,3
4
. You have a full-feature
ashlight from OpenGL Spy-Supplies In. whih behaves like a spot-light with a narrow one. Your
aim is to shine your ashlight on the painting when the eld-agent is in the ritial position so that
he sees the ode from his position but others ontinue to see the painting. All lighting parameters
available for any OpenGL light are ontrollable on the ashlight. The attenuation of the light from
the ashlight due to fog and distane has a onstant oeient of 1, a linear oeient of
8
143
ft
−1
and a quadrati oeient of 0. To make out the ode on the painting from the bakground there
must be a minimum dierene of
1
10
in eah of the R,G,B omponents of the olors reahing the
agent's eye from b oth materials.
1. What is the expression for the total olor observed by the eld-agent at a distane
d
from a
point of atual olor
(rp, gp, bp)
(after lighting alulations et) ? (3 pts)
2. What general settings would you hoose for your ashlight? (2 pts)
3. What is the maximum distane from the painting that the ode will be visible at all? (10 pts)
4. Supp ose the agent has parked himself at a total distane of 6 ft. from the painting and is 3
ft. to the left of the enter, where should you position yourself so that you an shine your
ashlight? What exat settings would you make on your ashlight? (10 pts)
Perform all alulations using rational numbers. All olors omponents are in the range
[0,1]
.
1
Do not try this at home!
2
The author's blurb by its side says that it is a full-length mirror and that a zen monk would be able to see his
silhouette in it in the same olor as the bakground
1
