UGC-NET | UGC NET CS 2018 Dec – II | Question 89

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 ever 0.

(A) Q and R only
(B) P only
(C) P and Q only
(D) P, Q and R


Answer: (C)

Explanation:

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