DDA line drawing algorithm Implementation in C-Language

Computer graphics programming can be written in computer languages like C, C++, java and many more.

DDA line drawing algorithm:

DDA ( Digital Differential Analyzer ) Algorithm is scan conversion of line. It accepts end points of line A(x1,y1) and B(x2,y2) , finds intermediate pixel location and display on display device.

we know line equation y=mx+c where m is slope and c is y-intercept as constant.

slope m=(y2-y1)/(x2-x1)

              = dy/dx      where  dx=(x₂-x₁)  and dy=(y₂-y₁)   

we can calculate dy if we know dx as dy=m.dx and  we can calculate dx if we know dy as dx=dy/m.

from above equation we can say if dx=1 then dy=m and if dy=1 then dx=1/m.

DDA algorithm increments by unit value in one coordinate and second coordinate can be calculated. Unit increment is based on slope. if abs(slope) <1 then increment by one in x coordinate and y coordinate increment  can be calculated by y_inc=m.

x_inc=1,y_inc=m

if abs(slope)>1 then increment by one in y coordinate and calculate x coordinate increment as x_inc=1/m.

y_inc=1,x_inc=1/m

using increment factor all intermediate values can be calculated as

x_next=x_current+x_inc

y_next=y_current+y_inc

this prcess is recurssive till we reach  last coordinate of line (x2,y2).

Algorithm Steps:

1.Accept input (x₁,y₁) and (x₂,y₂) as end points of Line

2. Calculate dx=(x₂-x₁)  and dy=(y₂-y₁).

3. If abs(dx)>=abs(dy)

               length=dx

       else

           length=dy

4. Calculate x_inc=dx/length and y_inc=dy/length.

5. Plot first pixel (x₁,y₁) .

6. Calculate x_next=x_current+x_inc  and y_next=y_current+y_inc and plot(x_next, y_next).

7. Repeat step 6 ,length times.   

8. Stop  

DDA line drawing algorithm Implementation in C-Language:

Program:

#include<stdio.h>
#include<graphics.h>
#include<math.h>
#include<conio.h>

void main()
{
int gd=DETECT,gm;
int i,len;
float x1,y1,x2,y2,dx,dy,xinc,yinc;
initgraph(&gd,&gm,"c:\\turboc3\\bgi");
printf("Enter x1");
scanf("%f",&x1);
printf("Enter y1");
scanf("%f",&y1);
printf("Enter x2");
scanf("%f",&x2);
printf("Enter y2");
scanf("%f",&y2);
dx=(x2-x1);
dy=(y2-y1);
if(abs(dx)>=abs(dy))
{
len=dx;
}
else
{
len=dy;
}
xinc=dx/len;
yinc=dy/len;
putpixel(x1,y1,4);
for(i=1;i<=len;i++)
{
x1=x1+xinc;
y1=y1+yinc;
putpixel(x1,y1,4);
}
getch();
}

Output: