CS335
Fall, 2008
Homework 9 (20 points)
Due: December 2, 2008 (Tuesday)

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1. (Polygon Clipping)
   To ensure a given polygon is clipped properly against a window,
   sometimes we have to use Weiler-Atherton's clipping algorithm.
   For that particular algorithm, if we are clipping a polygon 
   against the left boundary of a window, where should we start the
   clipping process? Justify your answer. (10 points)


2. (Rendering of B-spline Curve Segments)
   To render a cubic B-spline curve segment, one possibility is to
   convert the B-spline control points P0, P1, P2, and P3 into Bezier
   control points Q0, Q1, Q2 and Q3, using the following formula

                 Q1 = P1 + (P2 - P1)/3
                 Q2 = P1 + 2(P2 - P1)/3
                 A  = P1 + (P0 - P1)/3
                 B  = P2 + (P3 - P2)/3
                 Q0 = (A + Q1)/2
                 Q3 = (B + Q2)/2

   and then render it using techniques developed for cubic Bezier
   curve segments. Why do we know Q0, Q1, Q2 and Q3 defined the
   above way are the Beizer control points of the cubic B-spline
   curve? (5 points)


3. (Homogeneous Coordinates)
   What is the main reason for us to use homogeneous coordinates in
   computer graphics? Why?  (5 points)


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Put you solution set in a text file  and send the text file to me
(cheng@cs.uky.edu) before midnight of the due day.

           CS535 (Fall 2008)
           Solution of Homework 9
           Due: 12/2/09
           Name: xxxxxx xxxxxx