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

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