Computer Science 455
Instructor: R. P. Burton
Sixth Quiz

March 31-April 1, 2003

1. Once the conversion to a normalized view volume has taken place, the most efficient clipping operation is associated with the ____________ coordinates.
   • x
   • y
   • z
   • x and y
   • (none of the above, clipping is equivalently simple for all coordinates)
   (e)


2. In doing a perspective transformation to normalized view volume coordinates, the center of projection moves
   • to the location of the viewer's eye
   • to the center of the view plane
   • to a user-selected point on the view plane
   • far, far away
   (d)


3. Which of the following extends least easily to 3D?
   • Cohen-Sutherland
   • Liang-Barsky
   • Nicholl-Lee-Nicholl
   (c)


4. How many vanishing points can be associated with a single polyhedron?
   • just one
   • two
   • at most three
   • arbitrarily many
   (d)


5. The calculation of light intensities typically is done _______ removing hidden surfaces.
   • before
   • simultaneous with
   • after
   (c)


6. The manner in which light is reflected from a surface is determined primarily by
   • the characteristics of the light source
   • the characteristics of the surface
   (b)


7. Diffuse reflection occurs with
   • ambient light
   • point source light
   • both ambient and point source light
   • neither ambient nor point source light
   (c)


8. Specular reflection occurs with
   • ambient light
   • point source light
   • both ambient and point source light
   • neither ambient nor point source light
   (b)


9. Suppose you have ten point light sources randomly distributed throughout a scene. How many dot products do you expect to need to calculate per surface, assuming a constant intensity surface?
   • none
   • just one
   • ten
   • (This cannot be answered until the characteristics of the surface are learned.)
   (c)


10. Which of the following is NOT a consideration in determining specular reflection at a point on a surface?
    • the surface normal
    • the direction to the point light source
    • the direction to the viewer
    • (all are considerations)
    (d)


11. Constant shading is
    • something you settle for when you don't have the resource to smooth-shade
    • Sometimes realistic, depending on the characteristics of the scene
    (b)


12. Where does Gouraud shading first calculate intensities?
    • at (polygonal) surfaces
    • at vertices
    • along edges
    • along scan lines
    (b)


13. Where does Phong shading first calculate intensities?
    • at (polygonal) surfaces
    • at vertices
    • along edges
    • along scan lines
    (d)


14. In the Roberts' hidden line algorithm, what is tested to determine if it/they is/are interior to a polyhedron?
    • each vertex of every other polyhedron in the scene
    • each edge of every polyhedron not containing the edge
    • lines (parallel to the viewing axis) from the points along each edge of every polyhedron not containing the edge
    (c)


15. Coherence ____ be exploited to increase the efficiency of the Roberts algorithm.
    • can
    • cannot
    (a)


16. Suppose a scene consists of 10 polyhedra each of which overlaps at least one other polyhedron. Suppose the average polyhedron consists of 20 polygons. About how many faces qualify for back-face elimination?
    • probably none
    • 25%
    • half
    • 75%
    • probably all
    (c)


17. The back-face elimination calculation requires at least
    • the coordinates of three vertices of the face
    • the equation of the plane in which the face lies
    • the coordinates of just one of the vertices of the face
    • the z-coefficient (sometimes called C) of the equation in which the face lies
    (d)


18. Which additional algorithm do you recommend to complete the hidden element removal task of problem 16 if none of the polyhedra overlap in x or y?
    • none
    • the depth-buffer method
    • the scan-line method
    • the depth-sorting method
    • any of (b), (c), or (d)
    (a)


19. The polygons comprising the scene appear in random order. The algorithm in use is
    • the depth-buffer method
    • the scan-line method
    • the depth-sorting method
    (a)


20. In the depth-sorting method, the polygons appear
    • in random order
    • back to front
    • top to bottom
    (b)


21. What is the relationship between the number of cells of the frame buffer and the number of cells of the z buffer?
    • 1:1
    • 1:many
    • many:1
    • many:many
    (a)


22. Suppose the depth of a point on a polygon has been computed. The calculation of the depth of an adjacent point on the same polygon requires
    • a subtraction or addition
    • a multiplication or division
    • subtractions or additions, and multiplications or divisions.
    (a)


23. Two planar polygons "intersect" a particular scan line. All of the following spans are possible EXCEPT
    • a span which neither polygon "intersects"
    • a span which just one polygon "intersects"
    • a span which both polygons "intersect"
    • a span which "belongs" to one polygon sandwiched between two spans which "belong" to the other polygon
    • (no exceptions here)
    (e)


24. Is the following scenario possible? 1) two surfaces are sorted on "max Z," 2) the surfaces overlap in x, y, and z, 3) the vertices of the surface with the greater "max Z" are not farther away than the plane of the surface of lesser "max Z," 4) the vertices of the surface of lesser "max Z" are not closer than the plane of the surface of greater "max Z," 5) the projections overlap, and 6) the surfaces do not intersect.
    • yes
    • no
    (a)


25. Which of the following is NOT sufficient to terminate subdivision (as discussed in class) when applying the area subdivision method?
    • no surfaces intersect a quadrant
    • no surfaces intersecting a quadrant overlap
    • a surrounding surface is closer than other surfaces which intersect a quadrant
    • (all are sufficient to terminate subdivision)
    (b)


26. The efficiency of the area subdivision method is inversely proportional to the number of required subdivisions.
    • true
    • false
    (b)


27. Octree methods for visible surface presentation write octree nodes to the frame buffer
    • back to front
    • front to back
    (b)


28. All of the following algorithms can be adapted for hidden-LINE elimination except
    • z-buffer
    • scan-line
    • depth-buffer
    • area subdivision
    • (no exceptions here)
    (e)


29. All of the following algorithms lend themselves to transparency except
    • z-buffer
    • scan-line
    • depth-sort
    • area subdivision
    • (no exceptions here)
    (a)


30. Which of the following is/are appropriate for performing hidden-surface removal from a scene containing a Bezier (curved) surface?
    • z-buffer
    • scan-line
    • depth-buffer
    • area subdivision
    • (all of the above)
    • (none of the above)
    (e)


31. How many polygons should be used to represent one face of one brick which is covered with pits and grooves?
    • just one or two
    • one for each pixel
    • enough to provide pixel-level detail in areas of pits and grooves (probably several hundred of several thousand)
    (a)


32. The illusion of texture can be created by altering the ____ as a function of position across the surface.
    • surface normal
    • coefficient of reflection
    • either the surface normal or the coefficient of reflection or both
    (c)


33. Shadows can be created by
    • explicitly darkening a surface which cannot be "seen" from a point light source
    • failing to add a point light source contribution for a surface which cannot be "seen" from the point light source
    • either (a) or (b)
    (c)


34. Suppose individual pixel intensities for a particular system range between 0 and 7. Suppose pixels are treated as being 2 x 3. How many different levels of intensity are possible?
    • 8
    • 2 x 3 x 8
    • 2 x 3 x (8 - 1) + 1
    • 2 x 3 x (8 - 1)!
    • 8!/(2x3)
    (b)


35. Adding random noise to a scene
    • always degrades the appearance of the scene
    • sometimes improves the appearance of the scene
    (b)


36. A Gouraud-shaded image of an automobile, for example,
    • is always devoid of edges
    • can have both edges and smoothed surfaces
    (b)


37. The silhouette of a Gouraud-shaded image
    • is smoothed
    • is unchanged by the Gouraud-shading
    (b)


38. What particular deficiency of Gouraud shading does Phong shading overcome?
    • it's computational complexity
    • Mach bands
    • it's unsmoothed silhouette
    • (all of the above)
    (b)