DDA LINE DRAWING ALGORITHM

The digital deferential analyzer (DDA) may be a scan-conversion line algorithm supported calculating either ∆y or ∆x.

In this method calculation is performed at each step but by using results of previous steps.

The Algorithm as follows:

Step1: Start Algorithm

Step2: Declare x1,y1,x2,y2,dx,dy,x,y as integer variables.

Step3: Enter value of x1,y1,x2,y2.

Step4: Calculate dx = x2-x1

Step5: Calculate dy = y2-y1

Step6: If ABS (dx) > ABS (dy)
            Then step = abs (dx)
            Else

Step7: xinc=dx/step
            yinc=dy/step
            assign x = x1
            assign y = y1

Step8: Set pixel (x, y)-

Step9: x = x + xinc
            y = y + yinc
            Set pixels (Round (x), Round (y))

Step10: Repeat step 9 until x = x2

Step11: End Algorithm

Example: If a line is drawn from (2, 3) to (6, 15) with use of DDA. what number points will needed to get such line?

Solution: P1 (2,3)  P11 (6,15)
                x1=2
                y1=3
                x2= 6
                y2=15
                dx = 6 - 2 = 4
                dy = 15 - 3 = 12
                m =  dy/dx = 12/4

For calculating next value of x takes x = x +  1/m



C Program:

#include<stdio.h>

#include<conio.h>

#include<graphics.h>

#include<math.h>

main()

{

int gd=DETECT,gm;

int x1,y1,x2,y2,dx,dy,a1,a2,b1,b2,i;

float step,xinc,yinc,x,y;

char a[20],b[20],c[20],d[20];

clrscr();

initgraph(&gd,&gm," ");

printf("\nEnter the starting point");

scanf("%d%d",&x1,&y1);

printf("\nEnter the ending point");

scanf("%d%d",&x2,&y2);

cleardevice();

a1=x1;

a2=x2;

b1=y1;

b2=y2;

x1+=20;

x2+=20;

y1=470-y1;

y2=470-y2;

line(20,20,20,470);

line(20,470,590,470);

outtextxy(190,60,"**********DDA LINE DRAWING ALGORITHM**********");

sprintf(a,"%c%d%c%d%c",'(',a1,',',b1,')');

sprintf(b,"%c%d%c%d%c",'(',a2,',',b2,')');

outtextxy(15,15,"^y");

outtextxy(590,469,">x");

outtextxy(x1,y1,a);

outtextxy(x2,y2,b);

dx=x2-x1;

dy=y2-y1;

if(abs(dx)>abs(dy))

step=abs(dx);

else

step=abs(dy);

xinc=dx/step;

yinc=dy/step;

x=x1;

y=y1;

for(i=1;i<=step;i++)

{

putpixel(x,y,RED);

x=x+xinc;

y=y+yinc;

}

getch();

closegraph();

}

FOR OUTPUT CLICK HERE!!