Computer Science 455

Instructor: R. P. Burton

Third Quiz

October 10-11, 2005


Name _________________________________________ Score ____________/26


  1. Suppose a complicated image has been scan-converted into a rectangular region of the frame buffer, but needs to be translated into another, possibly overlapping region of the frame buffer. Which approach is best:

    1. Re-scan-convert the image in the new location

    2. move one scan-line at a time, starting with a corner of the scanned image that is not overlapped.

    3. Move one scan-line at a line, starting with a corner of the destination image that is not overlapped.

    4. Move one scan-line at a line, starting with an overlapped corner.


(d)


  1. Your data consists of eight variables. You wish to scale the data. How many entries in the scaling matrix consist on nonzero values?

    1. 8

    2. 9

    3. 16

    4. 17

    5. 18

    6. more than 18


(d) (assuming the scaling takes place about an arbitrary point; (b) otherwise)


  1. Suppose you wish to rotate (in 3D) about a line segment which determines an arbitrary axis. To calculate the sines and the cosines for the first angle of rotation, you should use the length of

    1. the line segment

    2. a projection of the line segment

    3. a projection of the projection of the line segment


(b)


  1. y points out, x points left, z points down. To rotate counterclockwise about y, the minus sign on the sine goes in the _____ row (where the top row is the “first” row).

    1. first

    2. second

    3. third

    4. fourth


(a)


  1. For three-dimensional data, reflections can occur relative to any of the following EXCEPT

    1. a point

    2. a line

    3. a plane

    4. (no exceptions here)


(d)


  1. Suppose the data is represented relative to 3D coordinate system A, but we would like to represent it relative to 3D coordinate system B. Which of the following is the correct approach?

    1. find a transformation which maps from A to B and apply it to the data

    2. find a transformation which maps from A to B and apply it to the coordinate frame A

    3. find a transformation which maps from B to A and apply it to the data

    4. find a transformation which maps from B to A an apply it to coordinate frame A


(c)


  1. 3D data can be sheared with respect to (pick the most inclusive answer)

    1. one coordinate

    2. any two coordinates, though no coordinate can be “sheared” relative to itself

    3. any two coordinates

    4. any three coordinates


(d)


  1. In traditional (i.e. early) graphics, a window is an area in

    1. display device space

    2. world coordinate space


(b)


  1. The relationship of a viewport to its space is identical to the relationship of a window to its space.

    1. true

    2. false


(b)


  1. Which makes the most sense?

    1. rotated window

    2. a rotated viewport

    3. both make (roughly) equivalently good sense

    4. neither makes much sense


(a)


  1. A change to a viewport produces _______ change in the scene; a change to a window produces _____ in the scene.

    1. a comparable, a comparable

    2. a comparable, a inverse

    3. an inverse, a comparable

    4. an inverse, an inverse


(b)


  1. The window-to-viewport mapping (with no rotation)

    1. is a direct mapping requiring no transformations

    2. requires only a translation

    3. requires only a scaling

    4. requires a scaling and a translation

    5. cannot be represented in matrix form (at least based on what has been discussed in class)


(d)


  1. In an affine transformation

    1. parallel lines remain parallel

    2. angles are preserved

    3. lengths are preserved

    4. (all of the above)

    5. (none of the above)


(a)


  1. All things considered, it is more efficient to clip to the

    1. viewport

    2. window

    3. (it makes no difference)


(a)


  1. If a window is rotated, the conventional clipping algorithms do not apply.

    1. true

    2. false


(b)


  1. ___________ is/are intended only for clipping regions with 2 vertical boundaries and 2 horizontal boundaries.

    1. Sutherland-Hodgman

    2. Weiler-Atherton

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


(a) (Sutherland-Hodgman can be adapted to work for any convex clipping polygon, but as presented in the text and other sources, it is for grid-aligned rectangles only)


  1. The Cohen-Sutherland algorithm is like playing tic-tac-toe; you try to get 3 “X”s in a line.

    1. true

    2. false


(b)


  1. The first test/activity in Cohen-Sutherland is

    1. attempt a trivial acceptance

    2. attempt a trivial rejection

    3. divide along a boundary


(a)


  1. The number of subdivisions in Cohen-Sutherland with midpoint subdivision is proportional to

    1. the length of the line segment

    2. the square of the length of the line segment

    3. the square root of the length of the line segment

    4. the log of the length of the line segment


(d)


  1. Liang and Barsky can determine all of the following except

    1. a line segment parallel to a boundary

    2. a line segment external (or internal) to a boundary

    3. whether a line segment enters or exits a boundary

    4. where a line segment passes through a boundary

    5. (no exceptions here)


(e)


  1. The primary activity of Nicholl Lee Nicholl is

    1. determining if a line segment is parallel to a boundary

    2. determining if a line segment passes through a boundary

    3. determining where a line segment passes through a boundary


(b)


  1. A clipping algorithm should be designed to accept polygons and produce _____.

    1. points

    2. lines

    3. points and lines

    4. polygons

    5. polygons and lines

    6. polygons, lines and points


(d)


  1. _________ can produce extraneous lines (which are not part of the original scene).

    1. Cohen-Sutherland

    2. Sutherland-Hodgman

    3. Weiler-Atherton

    4. (all of the above)


(b)


  1. To clip text (aligned with the vertical or horizontal boundaries), “all or nothing”

    1. clip the major diagonal of the text’s bounding box

    2. clip the minor diagonal of the text’s bounding box

    3. ((a) XOR (b), depending on the position of the text’s bounding box

    4. (a) or (b); both always work


(d)


  1. Curve clipping

    1. can be done using the algorithms referenced above

    2. is beyond the scope of CS 455


(a)


  1. Blanking

    1. can be done using the algorithms referenced above

    2. is beyond the scope of CS 455


(a)