Computer Science 455

Instructor: R. P. Burton

Second Quiz

February 5-6, 2007

Name _________________________________________ Score ____________/39

1. If you have a tablet with 1024 horizontal wires and 1024 vertical wires embedded in its surface, what is the minimum number of bits needed in a signal (in a wire) which permits the determination of an x,y position on the surface of the tablet?

   1. 1

   2. 10

   3. 20

   4. 1024

   5. 2048

(a)

2. If a tablet consists of two surfaces, one conductive and one resistive, and touching the surface is enough to bring the surfaces into contact with each other at the point of touch, the associated voltage drop is sufficient to communicate x and y position.

   1. true

   2. false

(a)

3. If you wish to use microphones and a “point” sound source to determine the 3D location of the “point” sound source, all of the following can be made to work EXCEPT

   1. three mutually perpendicular strip microphones

   2. two parallel strip microphones (one on each side of the tablet) and a perpendicular strip microphone (at the front or back of the tablet)

   3. three point microphones and corners of the tablet

   4. three point microphones along any one edge of the tablet

   5. (no exceptions in this list)

(e)

4. The Twinklebox had four spinning disks (with slits), each with two photomultiplier tube sensors. As a disk spun, it swept out a plane. When an LED was in the plane, light from the LED could pass through the slit and strike a photomultiplier tube. Even though eight planes were sweeping the room simultaneously, only three planes needed to be determined to learn the 3D location of the LED. Three photomultiplier tube sensors associated with a single disk would, in theory, be sufficient to make a determination of the LED’s 3D position.

   1. true

   2. false

(b)

5. Which of the following touch panels is likely to be least accurate?

   1. optical

   2. electrical

   3. acoustical

(a)

6. How was it possible for a light pen to leave a trail of light on the screen?

   1. the light pen wrote on a storage grid and a flood gun maintained the image

   2. the position of the light pen was sensed by infrared LEDs and sensors mounted along the edges of the screen

   3. the light pen responded to light from the screen which could be used to determine positions which could be stored

(c)

7. The “Rolls Royce” of graphics input systems is a voice input system, albeit expensive. It is superior to all other input systems for a majority of the logical graphics input activities.

   1. true

   2. false

(b)

8. The “writing utensil” in a mechanical plotter was

   1. a ballpoint or felt-tipped pen

   2. a laser pointer

   3. a carbide-tipped scribe

   4. any of the above

(d)

9. How is the ink in an inkjet printer deflected?

   1. by mechanically aiming the jet

   2. by electrically deflecting the ink

   3. by magnetically deflecting the ink

   4. it isn’t deflected; it simply plots a pixel at a time

(b)

10. What is the original source of the dominant contemporary (i.e. current) graphics standard?

    1. the SIGGRAPH Core

    2. PHIGS

    3. Silicon Graphics’ library

(c)

11. With the advent of raster displays, it was necessary, for the first time, to pick discrete points with which to represent a line segment on a graphics display.

    1. true

    2. false

(b)

12. A significant deficiency of the DDA line drawing algorithm is that fact that the programmer must choose between a line that may sit “underneath” or on the true line, or the expense of “round” (as opposed to “trunk”) operations and each pixel.

    1. true

    2. false

(b)

13. Which is likely to take more steps?

    1. the simple DDA

    2. the symmetric DDA

    3. (both take the same number of steps)

(b)

14. The starting decision parameter for the Bresenham line-drawing algorithm is p₀ = 2Δy – xΔ. What is the intuitive meaning of this expression?

    1. It represents the difference between the distance from the true line to the pixel center above and the distance from the true line to the pixel center below

    2. It represents the ratio of the distance from the true line to the pixel center above and the distance from the true line to the pixel center below

    3. Neither (a) nor (b)

(c)

15. If you have multiple parallel processors which can be used to scan-convert a line segment, it is probably not efficient to find an exploit cycles in the Bresenham decision variables. It’s probably better simply to divide the line segment into pieces of about the same size, assigning each to one of the processors.

    1. true

    2. false

(a)

16. The time involved to find the location in the frame buffer representing the starting pixel of a line segment is probably _____ the time involved to find the location in the frame buffer representing the next pixel of a line segment.

    1. less than

    2. the same as

    3. greater than

(c)

17. What’s wrong with using the explicit equation for a circle to determine points around its circumference?

    1. nothing

    2. it slow, even though it’s uniform

    3. it’s fast, but not uniform

    4. it’s slow and it’s not uniform

(d)

18. What’s wrong with using the parametric polar equations for a circle to determine points along its circumference?

    1. nothing

    2. it’s slow, even though it’s uniform

    3. it’s fast, but not uniform

    4. it’s slow and it’s not uniform

(b)

19. If a DDA algorithm is used to determine points along the circumference of a circle, the lesser of two evils is

    1. a figure that doesn’t close

    2. a figure that isn't a true circle

(b)

20. To calculate points along the circumference of a circle, only _____ of the circumference needs to be processed; the rest can be implied.

    1. one half

    2. one fourth

    3. one eighth

    4. one sixteenth

(c)

21. The pixels representing the circumference should be ____ the true circumference.

    1. immediately inside

    2. on

    3. immediately outside

(a)

22. Which quadrant of a circle requires the least adjustment in pixel positions to achieve the intent of the previous question? Assume a pixel’s position is the lower left corner of its bounding box.

    1. upper right

    2. lower right

    3. lower left

    4. upper left

(c)

23. Unlike the Bresenham line-drawing algorithm, the Bresenham circle-drawing algorithm requires more than additions, shifts, and subtractions to calculate successive decision variables.

    1. true

    2. false

(b)

24. Ellipses, parabolas, and hyperbolas, while standard geometric shapes, are not particularly useful in most graphics applications because shapes are rarely elliptical, parabolic, or hyperbolic.

    1. true

    2. false

(b)

25. The methods discussed in class for drawing ellipses, parabolas, and hyperbolas using the Bresenham approach are applicable ONLY if the shape is in “standard position,” i.e. aligned with the axes.

    1. true

    2. false

(b)

26. Suppose a particular polygon (to be scan-converted using the scan-line algorithm) consists of n vertices. Those n vertices function as either the starting point or the ending point of ____ spans of pixels.

    1. n-1

    2. n

    3. n + 1

    4. 2n

    5. (can’t say in general)

(e)

27. The ends of spans of pixels (to be used by the scan-line algorithm) can be found by “DDAing” along the edges, unit stepping in the

    1. x direction

    2. y direction

    3. direction of the axis of greatest excursion

(b)

28. This question was so ambiguous it was not graded and has been removed.

29. A recursive boundary-fill algorithm, processing a span of pixels at a time, must

    1. look horizontally for points along a boundary

    2. look vertically for points along a boundary

    3. either (a) or (b)

    4. both (a) and (b)

(d)

30. A recursive flood-fill algorithm _____ accommodate holes in the interior of the polygon.

    1. does

    2. does not

(a)

31. Which of the following poses the least problems:

    1. a 4-connect boundary and a 4-connect fill

    2. a 4 connect boundary and an 8-connect fill

    3. an 8 connect boundary and an 8-connect fill

    4. an 8 connect boundary and a 4-connect fill

(b)

32. If a point is “inside” a polygon, it’s inside, independent of whether the “edge crossings” test or the “winding number” rule is used.

    1. true

    2. false

(b)

33. A polygon consists on n vertices. Into how many polygons does it need to be split so that each polygon lies entirely in plane? Assume n >= 3.

    1. n

    2. n-1

    3. n-2

    4. n-3

    5. (can’t say in general)

(c)

34. When finding the equation of a plane using the technique discussed in class, the same equation results independent of which n (n > 3) vertices of a polygon are used, provided they are taken in a clockwise order.

    1. true

    2. false

(b)

35. When finding the equation of a plane using the technique discussed in class, the same equation results independent of whether the vertices of a polygon are taken in a clockwise order or counterclockwise order.

    1. true

    2. false

(b)

36. When filling a polygon with a repeating pattern (think “tiles”), the starting point for the first tile can be anywhere EXCEPT

    1. at a vertex

    2. at a corner of the bounding rectangle

    3. interior to the polygon

    4. outside the bounding rectangle

    5. (no exceptions here)

(e)

37. Characters can be generated from bit maps or from strokes. The approaches represent the classic trade-off between storage and processing.

    1. true

    2. false

(a)

38. What is a polymarker?

    1. a multi-colored stroke device (“brush”)

    2. a collection of unconnected vertices

    3. a single bit used to indicate that a polygon (in a collection of several polygons) has been scan-converted

(b)

39. The DDA and Bresenham line drawing algorithms are easily adapted to lines of varying thicknesses when you don’t care about the end caps.

    1. true

    2. false

(a)