# C: Line Drawing using DDA Algorithm [Straight, Dotted, Dashed]

INTRO
The following program carries out the task of drawing a line using DDA algorithm.
It also comes with the added features of drawing a dotted or dashed lines.

In computer graphics, a digital differential analyzer (DDA) is hardware or software used for linear interpolation of variables over an interval between start and end point. DDAs are used for rasterization of lines, triangles and polygons. In its simplest implementation, the DDA algorithm interpolates values in interval by computing for each xi the equations xi = xi−1+1/m, yi = yi−1 + m, where Δx = xend − xstart and Δy = yend − ystart and m = Δy/Δx.
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CODE
#include <stdlib.h>
#include <stdio.h>
#include <conio.h>
#include <math.h>
#include <graphics.h>

float x1,x2,y1,y2,dx,dy,len,ix,iy,x,y,s1,s2;
int i,j,ch;

int main()
{
int gd = DETECT, gm;
clrscr();
initgraph(&gd,&gm," ");
printf("Enter the first coordinates.");
printf("\nx1: ");
scanf("%f", &x1);
printf("y1: ");
scanf("%f", &y1);
printf("\nEnter the second coordinates.");
printf("\nx2: ");
scanf("%f", &x2);
printf("y2: ");
scanf("%f", &y2);

dx = abs(x2-x1);
dy = abs(y2-y1);
printf("\nThe value of DeltaX: %f.", dx);
printf("\nThe value of DeltaY: %f.", dy);

if(dy > dx)
{
len = dy;
}
else if(dx > dy)
{
len = dy;
}
else
{
len = dy;
}

printf("\nThe length is: %f", len);

ix = (x2-x1)/len;
iy = (y2-y1)/len;

printf("\nThe increment in X: %f.", ix);
printf("\nThe increment in Y: %f.", iy);
if((x2-x1) < 0)
{
x = x1 - 0.5;
}
if((x2-x1) > 0)
{
x = x1 + 0.5;
}
else if((x2-x1) == 0)
{
x = x1;
}

printf("\nThe value of init X: %f", x);

if((y2-y1) < 0)
{
y = y1 + (0.5*(-1));
}
else if((y2-y1) > 0)
{
y = y1 + 0.5;
}
else if((y2-y1) == 0)
{
y = y1;
}

printf("\nThe value of init Y: %f", y);

printf("\ni\tPlot\tX\tY\n");

printf("Press any key to continue to the graph...");
getch();
clrscr();

s1 = floor(x);
s2 = floor(y);

po:

printf("\nChoose from options below...");
printf("\n1 = Straight line");
printf("\n2 = Dotted Line");
printf("\n3 = Dashed Line");
printf("\n>>Enter you choice: ");
scanf("%d", &ch);

switch(ch)
{
case 1:
clrscr();
for(i=0;i<len;i++)
{
putpixel(s1,s2,4);
x = x+ix;
y = y+iy;
s1 = floor(x);
s2 = floor(y);
//printf("%d\t(%f,%f)\t%f\t%f",i,s1,s2,x,y);
}
break;
case 2:
clrscr();
for(i=0;i<len;i++)
{
if(i%2==0)
{
putpixel(s1,s2,4);
}
x = x+ix;
y = y+iy;
s1 = floor(x);
s2 = floor(y);
//printf("%d\t(%f,%f)\t%f\t%f",i,s1,s2,x,y);
}
break;
case 3:
clrscr();
for(i=0;i<len;i++)
{
if(i%4!=0)
{
putpixel(s1,s2,4);
}
x = x+ix;
y = y+iy;
s1 = floor(x);
s2 = floor(y);
//printf("%d\t(%f,%f)\t%f\t%f",i,s1,s2,x,y);
}
break;
default:
printf("Enter a proper value from 1 to 3.");
goto po;
}

getch();
closegraph();
return 0;
}

The above code was written in Turbo C.

Output:

This post first appeared on Code Walk, please read the originial post: here

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C: Line Drawing using DDA Algorithm [Straight, Dotted, Dashed]

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