Past Midterm and Exam Questions (PDF) - Student.cs.uwaterloo.ca ...

72 CS488/688 Introduction to Computer Graphics
71. A perspective transformation transform everything that’s behind the viewer (in the unprojected
space) to be in front of the viewer. Potentially, this could result in objects that are
behind the viewer erroneously appearing on the screen. How do avoid this problem?
72. After multipling a 3D point whose matrix is [x, y, z, 1] t by the perspective transformation
matrix, we get the matrix [A, B, C, D] t . What remains to complete the perspective transformation?
Be specific (i.e., show the final result in terms of A, B, C, and D).
73. When performing a lighting calculation, we attenuate the intensity of the light based on the
distance from the light to the point on a surface at which we are performing the lighting
calculation. However, we do not attenuate the intensity to account for the distance from the
viewer to the point on the surface.
Why do we attenuate the intensity in the former case but not in the latter case?
74. Shadow maps are one way of achieving shadows on an OpenGL renderer. Describe the shadow
map method and what hardware support/features are needed to use it.
75. Name (or describe or otherwise illustrate) the three real-time shadowing algorithms described
in class. Circle the one that could most easily be adapted for use in a ray tracer.
76. Give one specific example of how Pixar animators made use of the traditional Disney animation
principles to create more engaging characters in the animation Luxo Jr..
77. Explain in one or two sentences why the CMYK colour space is referred to as a “subtractive”
colour space.
78. The Sutherland-Hodgman clipping algorithm can be used to clip an arbitrary polygon P to
a convex window W. Below are four copies of the same rectangular window W. Draw a
quadrilateral (four-sided polygon) P for each window so
that the resulting clipped polygons have 3, 4, 5, and 6 sides.
79. Suppose you have three line segments that are parallel to the projection plane and are aligned
in 3D with the up axis of the screen, and whose perspective projections onto the screen are
shown in the following diagram: