Computer Science 455

Instructor: R. P. Burton

Second Quiz

September 26-27, 2005

Name _________________________________________ Score ____________/46

1. The implicit equation for a circle leads to an algorithm which generates points in a manner which is

   1. slow and shoddy

   2. fast and shoddy

   3. fast and not shoddy

   4. slow and not shoddy

(a)

2. The parametric equation for a circle leads to an algorithm which generates points in a manner which is

   1. slow and shoddy

   2. fast and shoddy

   3. fast and not shoddy

   4. slow and not shoddy

(d)

3. Once you have determined the coordinates of a point (a,b) on a circle, simple arithmetic leads immediately to the coordinate(s) of ____ other points on the circle.

   1. no

   2. one

   3. three

   4. seven

   5. fifteen

   6. more than fifteen

(d)

4. The (final version of the) circle-drawing DDA algorithm discussed in class produces

   1. a circle

   2. a helix

   3. an ellipse

(c)

5. The DDA line-drawing algorithm can be adapted easily to produce

   1. lines with an “odd multiple” thickness

   2. lines with an “even multiple” thickness

   3. both (a) and (b)

(c)

6. What is the intuitive meaning of the decision variable in the Bresenham line-drawing algorithm?

   1. there is none

   2. which of two pixel centers is closer to the true line

   3. how many points have been plotted since the coordinate of the axis of least excursion has been incremented

   4. how nearly complete is the drawing of the line

(b)

7. A stereo (viewing) box has

   1. no mechanical parts and no electrical parts

   2. mechanical parts

   3. electrical parts

   4. electrical and mechanical parts

(a)

8. Determining frame buffer locations associated with a line (or the circumference of a circle) takes _______ along the line (or the circumference).

   1. essentially the same amount of time for all points

   2. different amounts of time for different kinds of points

(b)

9. Suppose a scene is composed by randomly generating the color of each pixel. Which of the following techniques could be expected to reduce the amount of memory needed to store the scene?

   1. run-length encoding

   2. cell encoding

   3. both

   4. neither

(d)

10. Suppose the outline of a polygon is scan-converted into the frame buffer and the odd-parity rule is used to determine if a particular point is inside or outside the polygon. No point interior to the outline is of the same color as the outline. Counting the number of outline-colored pixels encountered in shooting a ray from the “particular point” until the ray is outside the polygon provides enough information to determine if the “particular point” is inside or outside the polygon.

    1. true

    2. false

(b)

11. The winding-number rule for inside/outside testing makes use of vector ____-products.

    1. dot

    2. cross

    3. dot of cross

(c)

12. A boundary-fill (or flood-fill) algorithm is most efficient if it processes a pixel and then considers

    1. the four neighboring pixels

    2. the eight neighboring pixels

    3. all the pixels on the same scan-line

(c)

13. Suppose a polygonal area is to be filled with tiles (i.e. a two-dimensional grid pattern). The first tile

    1. must be positioned so that its origin coincides with a vertex of the polygon

    2. must be positioned so that its origin is interior to the polygon

    3. can be placed anywhere

(c)

14. What is a polymarker?

    1. a marker with multiple attributes

    2. a collection of several markers

    3. a polyline with the connecting line segments omitted

(b)

15. Ax + By + Cz + D = 0 and –Ax – By - Cz – D = 0 represent

    1. the same plane (with the same normal)

    2. different planes (with different normals)

(b)

16. Points, when presented on a computer screen

    1. have no attributes other than position

    2. have one or more attributes other than position

(b)

17. Texture is meaningful for all of the following except

    1. lines

    2. polygons

    3. polyhedra

    4. (no exceptions here)

(d)

18. _____ be used to produce equivalent results for different lines with different orientations.

    1. The same intensity/pixel and pixel mask can

    2. The same intensity/pixel but a different pixel mask must

    3. The same pixel mask but a different intensity must

    4. A different intensity and a different pixel mask must

(d)

19. The slope of a line (to be represented with butt caps) is m. The slope of the butt cap is

    1. m

    2. –m

    3. 1/m

    4. -1/m

(d)

20. A round joint achieved by drawing a circle at the intersection of the two lines (forming the intersection) and of a diameter determined by the line thickness affects the appearance of

    1. The outside of the joint

    2. The inside of the joint

    3. both the outside and the inside of the joint

(a)

21. Color look-up tables were useful in the days when memory (for the frame buffer, for example) was expensive, but, at least for the present, have no practical use.

    1. true

    2. false

(b – color-table animation)

22. Soft fill is achieved by

    1. using the flood-fill algorithm to write the polygon into the frame buffer

    2. using the boundary-fill algorithm to write the polygon into the frame buffer

    3. mixing the color of a foreground polygon with the information already written into the frame buffer

(c)

23. What does it mean to “bundle” attributes?

    1. to compress attributes to make them more storage-efficient – a carry over from earlier days

    2. to treat attributes uniformly for all primitives (treating lines as degenerate planes, points as degenerate lines, etc.)

    3. to map user-specified attributes to attributes available on a the available output devices (for contexts with multiple attributes)

    4. to provide “desirable” collections of compatible attributes (usually based on aesthetic considerations)

(c)

24. What is the primary purpose of an “inquiry” function?

    1. to permit the user to discover how a particular effect was achieved

    2. to permit temporary changes to attributes

    3. to discover the feasibility/availability of an attribute of potential interest

(b)

25. The most inclusive example of a “line” which manifests aliasing is

    1. any line drawn on a raster CRT

    2. any line which is copied to a new location on a CRT

    3. the blank space left after a line on a CRT is rewritten with background color

(a)

26. A Merry-Go-Round has 10 horses. Each is a “horse of a different color.” You are looking through a doorway in which only one complete horse can be visible at any point in time. A complete new horse is visible every 3 seconds. You’re busy learning about Nyquist, but you wish to look through the doorway frequently enough to see every horse. How often should you sample?

    1. every 1.5 seconds

    2. every 3 seconds

    3. every 6 seconds

(a)

27. _____ determines which pixels are inside a finite-width line.

    1. Prefiltering

    2. Postfiltering

(b)

28. ______ determines the extent to which a pixel area is overlapped.

    1. Prefiltering

    2. Postfiltering

(a)

29. How is pixel phasing implemented on a typical monitor?

    1. by prefiltering

    2. by postfiltering

    3. it isn’t

(c)

30. When subpixel masks are used, more weight is given to subpixels near the

    1. true position of the line to be scan-converted

    2. center of the pixel

(b)

31. A green polygon and a blue polygon share a common 38° boundary. To make the boundary appear smooth, the boundary should be

    1. all green or all blue

    2. various shades of cyan (which is a mixture of green and blue)

    3. all black to clearly mark the boundary

(b)

32. Geometric transformations, as discussed in class, can change _____. (pick the most inclusive answer)

    1. position

    2. position and orientation

    3. position, orientation, and size

    4. position, orientation, size, and shape

    5. position, orientation, size, shape, and a reversal of the order in which vertices are encountered in a counterclockwise traversal

    6. position, orientation, size, shape, and the order in which vertices are encountered (to any permutation of the original order) in a counterclockwise traversal

(e)

33. A circle is most efficiently translated by

    1. generating the points around the circumference of the circle adding the translation factor to each point.

    2. translating the center of the circle, and then generating the points around its circumference.

(a)

34. Rotation of a polygon through “theta” degrees occurs

    1. around its first vertex (i.e. the vertex specified first)

    2. around its “center of mass”

    3. around the origin

(c)

35. Rotation of a polygon around it’s first vertex, around its center of mass, or around the origin may require

    1. translation

    2. multiple rotations

    3. the development of new computer graphics techniques

(a)

36. When a convex polygon which does not include the origin is scaled with a scaling factor > 1,

    1. its position remains fixed, but its size increases

    2. its position changes, but its size stays the same

    3. its position changes and it size increases

    4. neither its position nor its size changes

(c)

37. Two-dimensional translation, rotation, and scaling use a 3 x 3 transformation matrix (rather than a 2 x 2 transformation matrix) primarily to accommodate

    1. translation

    2. rotation

    3. scaling

(a)

38. The inverse of a translation, rotation, or scaling transformation is best achieve by using

    1. Gauss elimination with partial pivoting

    2. Gauss elimination with full pivoting

    3. Simple algebra and/or geometry

(c)

39. The inverse of translation, rotation, AND scaling (i.e. at least one of each) is best achieved by

    1. reapplying the same transformations in the same order (effectively “complementing”)

    2. applying the same transformations in the opposite order

    3. applying the inverses of the transformations in the same order

    4. applying the inverses of the transformations in the opposite order

    5. (it can’t be done; once the transformation is done, it is irreversible)

(d)

40. What transformation is represented by the following matrix:

-1 0 0

0 -1 0

0 0 1

1. rotation

2. scaling

3. reflection

4. (all of the above)

(d)

41. Reflection in 2D can be though of as occurring

    1. across a line

    2. through a point

    3. either (a) or (b)

(c)

42. Reflection across an arbitrary line which passes through the origin can be done ONLY by rotating the arbitrary line so that it lies along the y-axis, by reflecting across the y-axis, and by rotating so that the line returns to its original position.

    1. true

    2. false

(b)

43. Both of the following are possible EXCEPT

    1. reflection across an arbitrary line which does NOT pass through the origin

    2. reflection through an arbitrary point

    3. (both (a) and (b) are possible)

    4. (neither (a) nor (b) is possible)

(c)

44. What does it mean to “shear” a square?

    1. to cut one side, usually diagonally

    2. to cut two opposite sides, usually diagonally

    3. to cut all four sides, usually diagonally

    4. to adjust a coordinate based in the value of another coordinate

(d)

45. The inverse of a shearing matrix with a single shearing factor s is achieved b

    1. a shearing matrix with a single shearing factor –s

    2. a shearing matrix with a single shearing factor 1/s

    3. a shearing matrix with a single shearing factor -1/s

    4. (none of the above)

(a)

46. Suppose a transformation matrix scales along the 38° line. This can be shown to be equivalent to (or different from) shearing in x and in y simply by algebraically comparing the 38° line scaling matrix and the shearing matrix.

    1. true

    2. false

    3. (you can’t scale along a 38° line)

(a)