DIGITAL DIFFERENTIAL ANALYZER (DDA) ALGORTIHM

Algorithm

#define ROUND(a) ((int)(a+0.5))

voidlineDDA (int xa, int ya, int xb, int yb)

 {

int dx = xb - xa, dy = yb - ya, steps, k;

floatxIncrement, yIncrement, x = xa, y = ya;

if (abs (dx) > abs (dy) steps = abs (dx) ;

else steps = abs dy);

xIncrement = dx / (float) steps;

yIncrement = dy / (float) steps

setpixel (ROUND(x), ROUND(y) ) :

for (k=0; k<steps; k++)

{

x += xIncrement;

 y += yIncrement;

setpixel (ROUND(x), ROUND(y));

}

}

Algorithm Description:

Step 1 :Accept Input as two endpoint pixel positions

Step 2: Horizontal and vertical differences between the endpoint positions are assigned to parameters dx and dy (Calculate dx=xb-xa and dy=yb-ya).

Step 3:The difference with the greater magnitude determines the value of parameter steps.

Step 4 :Starting with pixel position (xa, ya), determine the offset needed at each step to generate the next pixel position along the line path.

Step 5: loop the following process for steps number of times

a. Use a unit of increment or decrement in the x and y direction

b. if xa is less than xb the values of increment in the x and y directions are 1 and m

c. if xa is greater than xb then the decrements -1 and – m are used.

Example: Consider the line from (0,0) to (4,6)

1. xa=0, ya =0 and  

     xb=4 yb=6

2. dx=xb-xa = 4-0 = 4 and

    dy=yb-ya=6-0= 6

3. x=0 and y=0 

4 > 6 (false) so,

steps=6

5. Calculate xIncrement = dx/steps = 4 / 6 = 0.66 and yIncrement = dy/steps =6/6=1

6. Setpixel(x,y) = Setpixel(0,0) (Starting Pixel Position)

7. Iterate the calculation for xIncrement and yIncrement for steps(6) number of times 

Advantages of DDA Algorithm

1. It is the simplest algorithm

2. It is a is a faster method for calculating pixel positions

Disadvantages of DDA Algorithm

1. Floating point arithmetic in DDA algorithm is still time-consuming

2. End point accuracy is poor