UGC NET CSE | December 2018 | Part 2 | Question: 43

Question

​​​​​​​Consider the midpoint (or Bresenham) algorithm for rasterizing lines given below:

1. Input $(x_1, y_1)$ and $(x_2, y_2)$
2. $y=y_1$
3. $d=f(x_1+1, y_1+1/2)$ //f is the implicit form of a line
4. for $x=x_1$ to $x_2$
5. do
6. plot$(x,y)$
7. if $(d<0)$
8. then
9. $y=y+1$
10. $d=d+(y_1-y_2)+(x_2-x_1)$
11. else
12. $d=d+(y_1-y_2)$
13. end
14. end

Which statements are true?

P: For a line with slope $m>1$, we should change the outer loop in line (4) to be over $y$

Q: Lines (10) and (12) update the decision variable $d$ through an incremental evaluation of the line equation $f$

R: The algorithm fails if $d$ is over $0$

Choose the correct answer from the code given below:

• A. P only
• B. P and Q only
• C. Q and R only
• D. P, Q and R