UGC NET CSE | August 2016 | Part 3 | Question: 15

Question

Consider the Breshenham’s line generation algorithm for a line with gradient greater than one, current point $(x_{ i} , y_{i} )$ and decision parameter, $d_{i}$. The next point to be plotted $(x _{i+1}, y_{i+1})$ and updated decision parameter, $d_{i+1}$, for $d_{i} < 0$ are given as _______.

• A. $x_{ i+1} = x _{i +1} y_{i+1} = y_{i} d_{i+1} = d_{i} + 2 dy$
• B. $x _{i+1} = x _{i} y_{i+1} = y_{i + 1} d_{i+1} = d_{i} + 2 dx$
• C. $x _{i+1} = x_{ i}  y_{i+1} = y_{i + 1}  d_{i+1} = d_{i} + 2 (dx – dy)$
• D. $x_{ i+1} = x_{ i + 1}  y_{i+1} = y_{i + 1} d_{i+1} = d_{i} + 2 (dy – dx)$

Answer 1

Correct option is A.

When di < 0 we choose east pixel and for next points increment X and no change in Y then add east pixel value to old di for new di.

When di > 0 we choose north east pixel and increment both X and Y and add value of North pixel to di.

When di = 0 we can choose any one of them to find next points to be plotted.

Hence, di < 0  is satisfied by option A.