Computer Science 455

Instructor: R. P. Burton

Second Quiz

February 2-3, 2004

 

Name _________________________________________    Score ____________/xx

 

1.                  What is an “output primitive?”

a.                   the fundamental output on an older (“primitive”) device such as a vector on a vector CRT

b.                  a basic geometric entity such as a point, a line, a circle, etc.

c.                   a pixel or other fundamental building block of a graphic image

 

(b)

 

2.                  Which of the following can always be drawn in precisely the right place(s) on a raster CRT?

a.                   a point

b.                  a line

c.                   a circle

d.                  (all of the above)

e.                   (none of the above)

 

(e)

 

3.                  The DDA algorithm draws lines which have

a.                   positive slope less than 1

b.                  positive slope greater than 1

c.                   negative slope between 0 and –1

d.                  negative slope between –1 and negative infinity

e.                   (all of the above)

 

(e)

 

4.                  What is the line length estimate for a symmetric-DDA line between (0,0) and (100,200)?  (pick the range in which the answer lies)

a.                   0 to 99

b.                  100 to 149

c.                   150 to 199

d.                  200 to 249

e.                   more than 249

 

(e – 256)

 

5.                  The Bresenham algorithm can be expected to produce a line that is _____ a simple DDA line in terms of the pixels chosen.

a.                   identical to

b.                  inferior to (albeit faster than)

c.                   superior to (albeit slower than)

 

(a)

 

6.                  What quantity is represented exactly by the decision variable in the Bresenham algorithm?

a.                   the (vertical or horizontal) distance from the closest pixel center to the true line

b.                  the (vertical or horizontal) distance from the farthest pixel center to the true line

c.                   the difference between (a) and (b)

d.                  the absolute value of (c)

e.                   (none of the above)

 

(e)

 

7.                  Suppose time t is required to determine the location in the frame buffer of first pixel of a DDA or Bresenham line.  About how much time is needed to determine the location in the frame buffer of the second pixel?

a.                   much less than t

b.                  t

c.                   much more than t

 

(a)

 

8.                  What’s wrong with using the implicit equation for a circle (solved for either x or y) for determining the pixels that lie along the circumference of the circle?

a.                   it’s relatively slow

b.                  it does not determine uniformly spaced pixels

c.                   both (a) and (b)

 

(c)

 

9.                  What’s wrong with using the parametric equation for a circle (solved for either x or y) for determining the pixels that lie along the circumference of the circle?

a.                   it’s relatively slow

b.                  it does not determine uniformly spaced pixels

c.                   both (a) and (b)

 

(a)

 

10.              The circle-generating DDA produces either a spiral or an ellipse; in general it does not produce a circle.

a.                   true

b.                  false

 

(a)

 

11.              In order to produce a Bresenham circle NOT centered at the origin, how much of the circle has to be “processed” even when symmetry is exploited? (“processed” means, “given an x, calculate the corresponding y value”).

a.                   One eighth

b.                  One fourth

c.                   One half

d.                  All of it

 

(a)

 

12.              In the Bresenham algorithm, the initial value of the decision variable is 5/4 – r.  What does 5/4 represent?

a.                   the aspect ratio of the screen

b.                  the inverse of the aspect ratio of the screen

c.                   the extent to which pixels must overlap in order to avoid gaps

d.                  (none of the above)

 

(d)

 

13.              To avoid increasing the intended lengths of lines and the intended diameters of circles, pixel coordinates should refer to

a.                   the center of the pixel

b.                  a corner of the box that circumscribes the pixel

 

(b)

 

14.              Pixels representing the circumference of a circle should be

a.                   entirely inside the circle

b.                  as closely centered as possible on the circle

c.                   entirely outside the circle

 

(a)

 

15.              If edges are properly ordered for the active edge list, all the edges between (and including) the earliest currently active edge and the latest currently active edge are active (i.e. are still intersecting scan lines, none of these edges being “exhausted”).

a.                   true

b.                  false

c.                   huh?

 

(b)

 

16.              What advantage is provided by using an active edge list?

a.                   faster processing

b.                  less storage

c.                   greater accuracy

 

(b)

 

17.              The odd-even rule and the nonzero winding number rule (for determining if a point is inside a polygon) perform (pick the most inclusive answer)

a.                   identically for convex polygons

b.                  identically for polygons which do not self-intersect

c.                   identically for all polygons

 

(b)

 

18.              For filling a polygon to its boundary by putting on a stack each of a pixel’s neighbors, the number of neighbors should be “a” if the boundary is “b”-connected.  The sum of “a” and “b” should be

a.                   either 8 or 16

b.                  12

 

(b)

 

19.              Suppose that instead of boundary filling only to neighbors, an “edge to edge” fill is done for the current pixel.  What is the maximum number of “seed” pixels that can be put on the stack for subsequent “edge to edge” filling?

a.                   just one

b.                  two

c.                   more than two

 

(c)

 

20.              If you are going to fill a polygonal region with “tiles,” the starting point for the first “tile”

a.                   must be at a vertex

b.                  must be along a horizontal or vertical edge

c.                   must be inside the polygonal region

d.                  can be anywhere relative to the polygonal region

 

(d)

 

21.              Which of the following operators is most likely to be used with “tiling?”

a.                   DIV

b.                  MOD

c.                   RND

d.                  ABS

 

(b)

 

22.              Suppose you have two identical characters (same character, same font, same style) except that one is 10 pt and the other is 50 pt.  If the 50 pt character is scaled to 1/5th its size, it is identical to the 10 pt character.

a.                   true

b.                  false

 

(b)

 

23.              What’s a polymarker?

a.                   a collection of markers

b.                  a multicolored drawing device

c.                   a tag identifying an object as a polygon

d.                  a mark bit used to distinguish a polygon from a polyline

e.                   a written certification left by a parrot when placing a wager

 

(a)

 

24.              If three point microphones were used with a stylus to create a 3D locator, the three microphones

a.                   must be colinear

b.                  must be coplanar, but not colinear

c.                   must be neither colinear nor coplanar

 

(b)

 

25.              Touch panels employ _____ techniques.

a.                   optical

b.                  electrical

c.                   acoustic

d.                  optical and electrical

e.                   optical and acoustic

f.                    optical, electrical, and acoustic

 

(f)

 

26.              Light pens are designed to

a.                   write to the storage grid of (now obsolete) DVSTs

b.                  activate screen phosphors by emitting a low intensity beam of electrons

c.                   respond to light on a display screen

d.                  provide a minimum weight input device to reduce (and, ideally eliminate) arm fatigue

 

(c)

 

27.              Which of the following “logical” activities is most naturally provided by a voice system?

a.                   keyboard

b.                  locator

c.                   stroke

d.                  valuator

e.                   pick

f.                    button

 

(e)

 

28.              The writing instrument in a mechanical plotter is

a.                   a pen

b.                  a laser

c.                   a carbide-tipped stylus

d.                  a pencil

e.                   (any of the above)

 

(e)

 

29.              How many of the following coordinate systems are often 3D: master coordinates, world coordinates, viewing coordinates, device coordinates?

a.                   one

b.                  two

c.                   three

d.                  all four

 

(c)

 

30.              What is the primary goal of graphics standards?

a.                   to maintain the integrity of the subdiscipline of computer graphics

b.                  to encourage the virtue or orderliness

c.                   to achieve commercial advantage

d.                  portability

 

(d)