Computer Science 455
Quiz 3
Instructor: R. P. Burton
1. Which of the following is most likely to be a marker?
a. a dot on a 2D graph showing a salary and the number of years of service
b. a vertex of a polyline or polygon
c. a “hot point” useful in selecting from among overlapping objects
d. a progress indicator into an active edge list
(a)
2. One of the principal disadvantages on breaking many-sided polygons into triangles is the need to calculate the equations of multiple planes, each such calculation requiring calculation of the value of a 3x3 determinant
a. true
b. false
(b)
3. In the planar equation Ax + By + Cz + D = 0, what does D represent?
a. the orientation of the plane
b. the distance of the plane from the origin
c. nothing of particular value
(b)
4. “Points,” as plotted on a monitor have no attributes except for location.
a. true
b. false
(b)
5. Line segments, as represented on a computer, can have all the following attributes EXCEPT
a. color
b. texture
c. width
d. (no exceptions here)
(d)
6. What is a color look-up table?
a. a palette of all colors available on a display
b. a subset of all colors available on a display
c. a list of memory addresses of all colors available on a display
d. a list of memory addresses of a subset of all colors available on a display
(c)
7. If a line segment is presented with butt caps or projected end caps, chances are it is drawn with
a. a variation on the DDA algorithm
b. a variation on the Bresenham algorithm
c. a fill algorithm of some sort
d. (none of the above)
(c)
8. A pixel mask is suitable for texturing a line, independent of its slope.
a. true
b. false
(b)
9. Why are attributes “bundled?”
a. to achieve compatibility
b. to give definitions to all attributes
c. to organize them into a hierarchy
(b)
10. Pick the best characterization of “soft fill.”
a. a border/boundary of the same color
b. an antialiased boundary
c. a fuzzy boundary
d. a color-blended fill
(d)
11. Which of the following represents antialiasing?
a. the elimination of duplicate references to graphics objects
b. the elimination of “ghosting” in animation
c. the blurring/smoothing of boundaries
(c)
12. When filling a polygon with a pattern, the origin of the pattern
a. must be at a vertex of the polygon
b. interior to the polygon
c. somewhere (but anywhere) relative to the polygon
(c)
13. When is kerning?
a. adjusting intercharacter spacing so that the distance between maxX of one character and minX of its successor is constant
b. adjusting intercharacter spacing so that the distance between characters appears to be uniform,
c. micropositioning of the electron beam to improve boundaries
d. determining an italic bitmap for a character, given a plain bitmap for the character
e. adjusting the thickness of strokes based on their directions
(b)
14. Aliasing comes about as a consequence of
a. introducing information which isn’t present
b. undersampling
(b)
15. Polygons are best translated by
a. adding a shift vector to each point as the polygon is scan-converted
b. translating the vertices and generating the polygon using the new vertices
c. doing a bit block transfer in world coordinates
(b)
16. Rotation always occurs about the origin. To rotate about an arbitrary point, it is necessary to translate the arbitrary point to the origin, perform the rotation, and translate the arbitrary point back to its original position.
a. true
b. false
(b)
17. For a polygon, which of the following is/are scaled with a scaling matrix that has nonzero values only on the diagonal?
a. the dimensions of the polygon
b. the displacement of the polygon relative to the origin
c. both (a) and (b)
(c)
18. Which of the following cannot be composed (with the other two) into a 2 x 2 matrix?
a. translation
b. rotation
c. scaling
d. (no exceptions here)
(a)
19. When an object that does not overlap the origin is scaled, its displacement from the origin changes. This can be corrected by
a. a translation to achieve the original displacement
b. a translation preceding the scaling and another translation following the scaling
c. either (a) or (b)
(c)
20. Suppose a large collection of vertices need to be scaled and then translated. If everything is represented in matrix form, what should occur first?
a. the composition of the vertex matrix and the scaling matrix
b. the composition of the vertex matrix and the translation
c. the composition of the scaling and translation matrices
d. it makes no difference
(c)
21. Pixel phasing ______ special hardware features.
a. requires
b. does not require
(a)
22. How many points in (3D) homogeneous coordinate space map to a point in (2D) coordinate space
a. none
b. one
c. two
d. more than 2
(d)
23. Which of the following transformations is not always invertible?
a. translation
b. scaling
c. rotation
d. (all are always invertible)
(b)
24. Matrix multiplication is
a. associative
b. commutative
c. both (a) and (b)
(a)
25. (Two-dimensional) scaling is either in x or in y or in both. An “arbitrary scaling direction” in the plane is not meaningful.
a. true
b. false
(b)
26. Reflection can be done across/through any of the following EXCEPT
a. a line that does not pass through the origin
b. a line that is not parallel to a principal axis
c. a point (other than the origin)
d. (no exceptions here)
(d)
27. Suppose a 3 x 3 transformation matrix has the value -1 in positions (1,1) and (2,2), with the value 1 in position (3,3) and the value 0 in all other locations. This is a ________ transformation. (assume (1,1) is the upper left corner)
a. reflection
b. scaling
c. rotation
d. (all of the above)
(d)
28. To invert a shearing transformation,
a. replace the shearing factor in the original transformation with its negative
b. replace the shearing factor in the original transformation with its inverse
c. replace the shearing factor in the original transformation with the negative of its inverse
d. reflect the shearing factor across the major diagonal of the transformation matrix
e. reflect the shearing factor across the major diagonal and invert it
(a)
29. The two-dimensional affine transformations discussed in class always have 0 0 1 for the bottom row, even when they are composed together.
a. true
b. false
(a)
30. Suppose the objects in a 2D scene are described relative to the origin of 2D world coordinates, but you’d like transform them to 2D viewing coordinates, and this may involve translation, rotation, scaling, and even reflection. How do you obtain descriptions relative to 2D viewing coordinates?
a. use a transformation which maps the 2D world coordinate frame onto the 2D viewing coordinate frame
b. use a transformation which maps the 2D viewing coordinate frame onto the 2D world coordinate frame
c. (it can’t be done by either (a) or (b))
d. (it can be done only if no scaling is involved)
e. (it can be done only if no reflection is involved)
(b)
31. A complicated object has been scan-converted into a rectangular region of the frame buffer. To transfer the contents to a rectangle of the same shape and in the same orientation elsewhere in the frame buffer
a. begin with an overlapped corner of the source rectangle
b. begin with a nonoverlapped corner of the source rectangle
c. (it can’t be done in general)
(a)
32. Suppose the y-axis points down and the x-axis points right, and you want to rotate clockwise through 23.65°. Where does the minus sign go? (assume (1,1) is the upper left corner)
a. (1,1)
b. (1,2)
c. (2,1)
d. (2,2)
(b)