Computer Science 455
Instructor: R. P. Burton
Second Quiz
September 30-31, 2003
Name
_________________________________________ Score
____________/xx
1.
The “data glove” uses
a.
micropotentiometers to measure joint angles
b.
electromagnetic coupling between transmitting and receiving antennae
c.
acoustic coupling between ultrasonic transmitters in the glove and
point microphones near the monitor
(b)
2.
Suppose you have a graphics tablet with a rectangular grid of wires
embedded in the surface – 1024 wires running top to bottom and 1024 wires
running right to left. Suppose each wire
carries a binary code which can be sensed by a stylus. What is the minimum number of bits needed
(and used) for the binary code carried by a wire?
a.
less than 10
b.
10
c.
11
d.
more than 11
(b)
3.
An acoustic tablet with strip microphones along any three edges can
determine a unique point in the 3D space above the tablet.
a.
true
b.
false
(a)
4.
The Lincoln Wand had point microphones at the corners of a
rectangle. Microphones needed to be at
____ corners to determine the location of a point in 3D space.
a.
two
b.
three
c.
all four
(b)
5.
Touch panels (for making selections from the display surface) permit
input to be received using _____ methods.
a.
optical
b.
acoustical
c.
electrical
d.
(any of the above)
e.
(none of the above)
(d)
6.
The Light Pen is able to detect (and hence select) a screen position
using ____ methods.
a.
optical
b.
acoustical
c.
electrical
d.
(any of the above)
e.
(none of the above)
(a)
7.
Any of the physical input devices discussed in class can be made to
function as any of the logical input devices discussed in class.
a.
true
b.
false
(a)
8.
The units of world coordinates should be
a.
pixels
b.
inches or centimeters (depending on the local common unit)
c.
between 0 and 1 in each dimension
d.
the units of the application (perhaps microns, feet, parsecs, whatever)
(d)
9.
What is the purpose of normalized device coordinates?
a.
to accommodate the GKS standard
b.
to assure that all graphics development is done with a common
coordinate system
c.
to accommodate a variety of output devices
(c)
10.
A DDA line is drawn by stepping exactly one unit in x or in y,
depending on the slope of the line.
a.
true
b.
false
(a)
11.
Suppose you wish to draw a line between (10,20)
and (37,5). How does the number of
pixels “set” in the frame buffer differ for a simple DDA line in comparison to
a symmetric DDA line?
a.
exactly the same number of pixels is set
b.
the symmetric DDA typically will
set a few more pixels
c.
the symmetric DDA typically will set twice as many pixels
d.
the simple DDA typically will set twice as many pixels
e.
the simple DDA typically will set a few more pixels
(b)
12.
What is the best way to cause the DDA algorithm to set pixels on both
sides of the true line?
a.
Use the symmetric DDA algorithm
b.
Round instead of truncating
c.
Add 0.5 to the initial coordinate associated with the axis of least
excursion
d.
In general, this problem has no solution
(c)
13.
The Bresenham line algorithm exploits the fact that the “next” pixel to
be “set” is always
a.
either to the right, above, or to the right and above
b.
always one of eight adjacent pixels
c.
one of only two possible pixels
d.
consistently to the right, consistently above, or consistently to the
right and above
(c)
14.
For lines of other than minimal length, Bresenham outperforms DDA and
symmetric DDA because
a.
it always “sets” fewer pixels
b.
there is relatively little “overhead” work before it can start
determining pixels to be “set”
c.
it uses only simple operations like add, subtract, and shift
d.
it identifies and exploits repeating patterns in determining pixels to
be “set”
(c)
15.
Suppose time t is required to find the location, in the frame buffer,
of the first point of a Bresenham line.
How much time is required to find the location, in the frame buffer, of
the next point of the same line?
a.
much less than t
b.
t
c.
much more than t
(a)
16.
The implicit equation of a circle, unsolved for either x or y, is
insufficient to scan-convert the circle.
a.
true
b.
false
(b)
17.
The
parametric polar form of a circle (x = rcos(theta), y =
rsin(theta))
a.
determines points uniformly along the circumference of the circle and
is at least as efficient as any of the circle algorithms discussed in class
b.
determines points uniformly along the circumference of the circle but
is less efficient than some of the circle algorithms discussed in class
c.
does not determines point uniformly along the circumference of the
circle but is at least as efficient as any of the circle algorithms discussed
in class
d.
does not determine points uniformly along the circumference of the
circle and is less efficient than some of the circle algorithms discussed in
class
(b)
18.
The circle-generating DDA algorithm produces a near-circle which is
either a helix or an ellipse. Which is
preferable for a typical computer graphics application?
a.
the helix
b.
the ellipse
(b)
19.
The midpoint circle algorithm presented in class sets the initial value
of the decision variable to 5/4 – r.
What does the “5/4” represent?
a.
the aspect ratio of a conventional display
b.
the aspect ratio dictated by the “golden mean”
c.
the result of an algebraic derivation without any obvious meaning
(c)
20.
When a point along the circumference of a circle is determined using
any of the techniques discussed in class, but the circle is not centered at the
origin, ___ other point(s) along the circumference of the circle can be
determined with simple operations such as (but perhaps not limited to) negation
and swapping.
a.
no
b.
one
c.
three
d.
seven
e.
more than seven
(d)
21.
If the objective is to produce a representation of a line on the screen
which is as close as reasonable to the true line, screen coordinates should
refer to the locations of
a.
pixel centers
b.
corners of boxes circumscribing pixels
(b)
22.
As discussed in class, which is preferable for a representation of the
circumference of a circle? Pixels which
lie
a.
entirely inside the circumference
b.
as nearly as possible on/overlapping the circumference
c.
entirely outside the circumference
(a)
23.
Suppose that the vertices of a polygon, in counterclockwise order, are
at (100,0), (300,0), (100,200), and (0,100). How many vertices generate two scan-line
intersection points for the scan-line algorithm?
a.
one
b.
two
c.
three
d.
four
(a
– (100, 200))
24.
For the polygon of the previous problem, what is the maximum number of
edges on the active edge list at some point in the scan-conversion process?
a.
one
b.
two
c.
three
d.
four
(b)
25.
Points determined by the odd-even rule (a.k.a. the odd parity rule or
the even parity rule) to be exterior to an arbitrary polygon also are
determined by the (nonzero) winding number rule to be exterior to the polygon,
whether or not the polygon is self-intersecting.
a.
true
b.
false
(b)
26.
If the boundary is b-connected
and the fill technique is f-connected,
the sum of b and f should be ___ so that the polygon is filled completely, but the
fill does not seep outside the polygon.
a.
8
b.
12
c.
16
d.
8 or 16
(b)
27.
Suppose a convex polygon can be enclosed in a bounding box measuring
100 x 100. Suppose the polygon is
efficiently flood-filled, starting with an arbitrary point in its
interior. What is the maximum number of
points which might be on the stack, where the stack contains points from which
filling should be done?
a.
2
b.
100
c.
200
d.
much more than 200
(a)
28.
Suppose an arbitrary polygon is to be filled with “tiles,” each of
which contains a pattern. Suppose
further than the tiles may contain arbitrary collections of colors. Which fill algorithm is more appropriate?
a.
boundary fill
b.
flood fill
c.
boundary fill and flood fill are equally suitable
d.
neither boundary fill not flood fill is suitable
(a)
29.
Where must the starting point of the first potential “tile” (from the
previous question) be?
a.
at some vertex of the polygon
b.
interior to the polygon and not at a vertex
c.
virtually anywhere on the plane of the polygon
(c)
30.
(Graphic) points can have attributes in addition to location; (graphic)
line segments can have attributes in addition to starting point, ending point,
and length.
a.
true
b.
false
(a)
31.
Suppose the horizontal line from (0,0) to
(b,0) contains 100 pixels. Suppose the
vertical line from (0,0) to ( 0,c) contains 100
pixels. How many pixels are contained in
the diagonal line from (0,0) to (b,c)?
a.
100
b.
141
c.
142
(a)
32.
How many bits/pixel are represented by a frame buffer which can present
1024 colors from a palette of 16 million?
a.
8
b.
10
c.
24
d.
log216 million
(b)
33.
What is “soft fill”?
a.
Blurring edges so that, for example, boundaries between adjoining
polygons do not show a “stairstep” artifact.
b.
Filling with other than a pure hue.
c.
Adjusting intensity as a polygon is scan-converted that that its color
is mixed with the background color.
(c)
34.
Even with correctly bundled attributes, a line which the user chooses
to be black might be displayed in orange.
a.
true
b.
false
(a)
35.
Inquiry functions are intended primarily to permit a combination of
attributes to be deciphered (somewhat like learning what Colonel Sander’s 11
herbs and spices are), so that they can be copied and used at a later date in a
different context.
a.
true
b.
false
(b)
36.
An alias is a feature of a scene that
a.
is present, but shouldn’t be
b.
isn’t present, but should be
c.
has been corrected so that only features which should be present are
present
(a)
37.
Which is likely to produce more accurate results?
a.
supersampling (a.k.a. postfiltering)
b.
area sampling (a.k.a. prefiltering)
c.
both, since they produce identical results
(b)
38.
The boundary between a scan-converted red polygon and a scan-converted
green polygon actually looks cleaner and crisper if there is a narrow band with
various tones of yellow between the two polygons. In fact, the yellow band virtually
disappears, with only red and green being apparent. Further, the Bresenham line-drawing algorithm
can be adapted so that the amounts of red and green mixed to produced
the yellow can be determined from the decision variable.
a.
true
b.
false
(a)
39.
To change orientation of a polygon means (technically speaking)
a.
to translate it
b.
to rotate it
c.
to translate and/or rotate it
(b)
40.
Suppose a polygon of 80 vertices is to be translated. A common value is added to all x-coordinate values, and another (possibly the same) common value is
added to all the y-coordinate values.
a.
true
b.
false
(a)
41.
Which of the following transformations cannot be represented
practically in 2 x 2 matrix form?
a.
translation
b.
scaling
c.
rotation
d.
(no exceptions here; all can be represented practically)
(a)
42.
Scaling permits all of the following operations on polygons EXCEPT
a.
enlarging or shrinking
b.
mirror-imaging (across an axis, for example), or undoing of a mirror
image
c.
flattening
completely or unflattening (“re-inflating”?)
d.
(no exceptions here)
(c)