Computer Science 455

Instructor: R. P. Burton

Third Quiz

February 20-21, 2007

Name _________________________________________ Score ____________/38

1. Which approach would be more suitable for end caps for lines?

   1. an adapted DDA or Bresenham

   2. a polygon fill technique

   3. neither (a) nor (b) is suitable

(b)

2. Which of the following joint techniques may require a small, additional triangle?

   1. mitre

   2. round

   3. bevel

(c)

3. If someone tells you that their graphics system can display 4096 out of more than 16 million colors, they don’t understand the architecture of their graphics system.

   1. true

   2. false

(b)

4. If a red polygon (in front of a blue background) is soft-filled, you should expect it to be

   1. red

   2. light red

   3. dark red

   4. blue

   5. purple

(e)

5. What is the purpose for bundling attributes?

   1. to make sure no attribute is left unspecified

   2. to make compatible choices

   3. to provide for the interpretation of any choices for any available output device

(c)

6. In a graphics context, what is an alias?

   1. an artifact in the presentation that is not in the geometry, topology, or attributes

   2. a duplicate reference to the same graphics object

   3. a previous attribute value

(a)

7. Which is the correct association?

   1. supersampling / prefiltering, area sampling / postfiltering

   2. supersampling / postfiltering, area sampling / prefiltering

(b)

8. How is pixel phasing accomplished?

   1. by prefiltering

   2. by postfiltering

   3. by having the needed hardware

(c)

9. Suppose a rectangular region, aligned with the coordinate axes, is to be translated, but the resulting rectangular region overlaps the original rectangle region. If you want to do a block transfer,

   1. start with an overlapped vertex of the source rectangle

   2. start with a nonoverlapped vertex of the source rectangle

   3. it is necessary to re-scan-convert the rectangular region in its new position

(a)

10. A block transfer which involves a rotation of other than a multiple of 90 degrees is not possible for two overlapping blocks.

    1. true

    2. false

(b)

11. All of the following can be represented practically with a 2 x 2 transformation matrix except

    1. 2D translation

    2. 2D rotation

    3. 2D scaling

    4. (no exceptions here)

(a)

12. A scaling transformation can affect

    1. the dimensions of the shape being scaled

    2. the displacement (from the origin) of the shape being scales

    3. both (a) and (b)

(c)

13. All of the following transformation always have inverses (which can be used to restore the original conditions) except

    1. translation

    2. rotation

    3. scaling

    4. (no exceptions here)

(c)

14. How many points in homogeneous coordinate space correspond to a typical point in 2-dimensional space?

    1. just one

    2. exactly two

    3. exactly four

    4. more than four

(d)

15. An arbitrary point is translated to the origin, then an object is scaled or rotated relative to that arbitrary point, and finally the arbitrary point is returned to its original position

    1. to actually scale or rotate relative to the point (in common practice)

    2. to derive the transformation to scale or rotate relative to the point

(b)

16. In general, transformations such as translation, rotation, and scaling are

    1. associative

    2. commutative

    3. both (a) and (b)

(a)

17. An object can be scaled in its x-direction and/or its y-direction, but not in a direction which is not parallel to either its x-direction or its y-direction.

    1. true

    2. false

(b)

18. The inverse of a composite transformation can be found practically by all of the following with the possible exception of

    1. Cramer’s rule

    2. Gauss elimination with partial pivoting

    3. An appropriate composition of inverses of the component transformations

    4. (no exceptions here)

(a)

19. The inverse of a rotation matrix is

    1. simply the migration of the minus sign from one sine to the other

    2. changing of the signs on all the sines and cosines

    3. neither (a) nor (b)

(a)

20. The arbitrary transformation of a 2D shape (possibly including translation, rotation, and/or scaling) anticipates the calculation of ____ elements of composite transformation matrix.

    1. 3

    2. 6

    3. 7

    4. 9

(b)

21. Suppose an arbitrary shape is 1) rotated 180 degrees, 2) reflected through the origin, 3) scaled by -1 in both x and y, and 4) rotated -180 degrees. How has the shape changed?

    1. not at all

    2. it’s reflected across the x-axis

    3. it’s reflected across the y-axis

    4. it’s reflected through the origin

    5. (none of the above)

(a)

22. All of the following reflections can be represented in matrix form EXCEPT reflection (pick the most inclusive correct answer)

    1. across a line that is not parallel to a principal axis

    2. across a line that does not pass through the origin

    3. across a line that is not parallel to a principal axis and does not pass through the origin

    4. through the origin

    5. through an arbitrary point

    6. (no exceptions here)

(f)

23. Suppose a shape is defined relative to a coordinate frame A, and the position, orientation of coordinate frame A is defined related to coordinate frame B. Which transformation can be applied to the shape to define it relative to coordinate frame B? A transformation which

    1. maps A onto B

    2. maps B onto A

    3. either (a) or (b)

(b)

24. Shearing can be thought of as “scaling based on the value of another coordinate.”

    1. true

    2. false

(a)

25. When a shape is sheared, the dimensions and angles of the resultant shape are determined by

    1. the dimensions and angles of the original shape

    2. the dimensions, angles, and position of the original shape

(a)

26. The matrix element in the inverse of a shearing transformation is

    1. the reciprocal of the original shearing element

    2. the negative of the original shearing element

    3. the negative of the reciprocal of the original shearing element

    4. (none of the above)

(b)

27. The x-axis points left and the y-axis points down. Where does the minus sign go for counter-clockwise rotation?

    1. (1,1)

    2. (1,2)

    3. (2,1)

    4. (2,2)

(b)

28. The x-axis points left, the y-axis points down, and the z-axis points in. Where does the minus sign go for counterclockwise rotation “about y”?

    1. (1,2)

    2. (1,3)

    3. (2,1)

    4. (2,3)

    5. (3,1)

    6. (3,2)

(b)

29. Suppose you are modeling the elements of a 12D world, and you wish to transform its contents. How big is the associated transformation matrix?

    1. 4 x 4

    2. 11 x 11

    3. 12 x 12

    4. 13 x 13

(d)

30. In 3D is makes the least intuitive sense to reflect _______.

    1. through a point

    2. across a line

    3. across a plane

(b)

31. A 3D translation matrix can involve 3 translation factors; a 3D scaling matrix can involve 3 scaling factors. A 3D shearing matrix can involve ___ shearing factor(s).

    1. 1

    2. 3

    3. 4

    4. 6

    5. 9

(d)

32. Traditionally, a “viewport” is an area

    1. of the world coordinate system to be displayed

    2. an area of the display device

(b)

33. The “viewing transformation” often consists of a scaling and a translation.

    1. true

    2. false

(a)

34. Which makes less sense?

    1. a rotated window

    2. a rotated viewport

    3. (both make equivalently good sense)

(b)

35. A change to the _____ often produces a corresponding change in the presentation; a change to the ____ often produces an inverse change in the presentation.

    1. window, viewport

    2. viewport, window

(b)

36. All things considered, in a 2D world it is more efficient for the software to clip to the ______.

    1. window

    2. viewport

(b)

37. Pick the statement which best characterizes the Cohen-Sutherland algorithm.

    1. All lines interior to the clipping region are trivially accepted

    2. All lines exterior to the clipping region are trivially rejected

    3. Both (a) and (b) characterize this algorithm correctly

(a)

38. A significant disadvantage of Cohen-Sutherland with midpoint subdivision is the numerous divisions typically needed to find the intersection of a line segment with a clipping region boundary.

    1. true

    2. false

(b)