Computer
Science 455
Instructor: R. P. Burton
Second Quiz
May 19-20, 2003
Name
_________________________________________ Score
____________/26
1.
Pick the LEAST desirable of the following screen
grid coordinates options:
a.
grid intersections are pixel lower left corners
b.
grid intersections are pixel centers
c.
grid intersections are pixel upper right corners
(b)
2.
Pick the MOST accurate of the following options for
scan-converting the circumference of an ellipse.
a.
pixel centers should be inside the circumference
b.
pixel centers should be on the circumference
c.
pixel centers should be outside the circumference
(a)
3.
For the scan line algorithm, vertices should be
a.
counted only once, even though they belong to two
line segments
b.
counted twice, since they belong to two line segments
c.
sometimes (a), sometimes (b), and sometimes they are
not counted at all!
(c)
4.
Intersections of scan lines with polygon boundaries
should be found by
a.
DDAing along the edges of the
polygon, always stepping in y
b.
DDAing along the edges of the
polygon, always stepping in the axis of greatest excursion
c.
Using standard trigonometric methods to find the
intersections of two lines
(a)
5.
Suppose you wish to produce a sorted edge table,
containing edges in order of decreasing y of the highest (with the greatest y
value) vertex associated with the edge.
Suppose two edges proceed downward from the same vertex. Assume the origin of coordinates to be in the
lower left corner. Which edge is first
in the table?
a.
the edge on the left or the edge on the right, being
consistent for all such vertices
b.
the edge encountered first in clockwise or
counterclockwise order, being consistent for all such edges
c.
the shorter of the two edges
d.
the longer of the two edged
e.
the edge whose other endpoint has the greater y
value
f.
the edge whose other endpoint has the lesser y value
(e)
6.
Is it possible for an edge in the active edge list
(as discussed in class) to be inactive for a particular scan line?
a.
yes
b.
no
(a)
7.
Suppose you have a really hairy (but not
self-intersecting) polygon of 100 edges (maybe a shark took a bite out of
it). Suppose you pick a point and extend
it well beyond the polygon, but not through any vertices, and suppose this
extension crosses 95 edges. Is the point
inside or outside the polygon?
a.
inside
b.
outside
c.
can’t say
(a)
8.
Continuing the previous problem, suppose you count
instead the number of crossings from the left and the number of crossings from
the right, and this turns out that there are more from the left than from the
right. Is the point inside or outside
the polygon?
a.
inside
b.
outside
c.
can’t say
(a)
9.
Suppose a polygon to be boundary-filled with red has
a “British racing green” boundary and a few “British racing green” pixels
inside the boundary. Fortunately, these
pixels do not close off any part of the polygon.. Will the boundary fill algorithm be able to
do its job?
a.
no
b.
yes
(a)
10.
Suppose a polygon to be flood-filled with “British
racing green” has a few “British racing green” pixels inside the boundary, but
these pixels do not close off any part of the polygon.. Will the flood fill algorithm be able to do
its job?
a.
no
b.
yes
(b)
11.
x-connected boundaries require y-connected
fill. The sum of x and y should be
a.
8 or 16
b.
12
(b)
12.
What of the following would stop a flood-fill
algorithm from flooding in a particular direction from a particular point?
a.
encountering pixels of the flood-fill color
b.
finding no more “old color” pixels to replace
c.
both (a) and (b)
d.
neither (a) nor (b)
(c)
13.
Suppose you two marker symbols at (10, 20) and (100,
200), respectively. How many marker symbols
should be generated in between
a.
probably none
b.
about 90
c.
about 180
d.
more than 180
(a)
14.
How many of the following five “primitives” can have
attributes? points, lines, curves,
areas, characters
a.
all five
b.
four
c.
three
d.
two
e.
one
f.
none
(a)
15.
Pixels masks ____ adjusted for slope to produce
uniform lines.
a.
need not be
b.
need to be
(b)
16.
Suppose your system is capable of displaying 224
colors. By what amount does each cell of
the frame buffer decrease (how much less memory does it require) if your system
include a color look-up table of size 212?
a.
none
b.
1 bit
c.
2 bits
d.
12 bits
e.
23 bits
(d)
17.
When filling with a pattern, which of the following
operators is likely to be used?
a.
trunc
b.
round
c.
div
d.
mod
(d)
18.
Which of the following is likely to be most
memory-intensive?
a.
bitmap fonts
b.
outline fonts
c.
(they take the same amount of memory)
(a)
19.
The DDA algorithm adapts well to lines of _____
thickness.
a.
odd
b.
even
c.
both odd and even
(c)
20.
Suppose the color/intensity of the background is
100. Suppose the color/intensity of the
polygon is 200. Suppose the polygon is
40% transparent. What color/intensity
should be written into the frame buffer?
a.
100
b.
200
c.
140
d.
150
e.
160
(e)
21.
What is the primary purpose of a bundle table?
a.
to facilitate double buffering
b.
to represent that characteristics of each output
device
c.
to represent how attributes should be interpreted on
different output devices
d.
to reduce the size of the frame buffer by routing
output from the frame buffer through the bundle table, and then to the display
(c)
22.
What is aliasing in the
context of computer graphics?
a.
allowing multiple references to a single object
b.
distortion due to undersampling
c.
getting rid of the “jaggies”
(b)
23.
Doing calculations as if the screen is covered by a
finer grid of pixels than is actually available is called
a.
supersampling
b.
area sampling
c.
pixel phasing
(a)
24.
Calculating the extent to which a pixel is
overlapped is called
a.
supersampling
b.
area sampling
c.
pixel phasing
(b)
25.
Micropositioning the electron beam to shift
individual pixel positions is called
a.
Utter nonsense
b.
pixel phasing
(b)
26.
Pixel overlap can be determined by considering not
only the sign of the Bresenham-type decision
parameter, but also the magnitude.
a.
true
b.
false
(a)