Simple Line Drawing Algorithm using graphics.h

line.cpp

#include <iostream.h>
#include <math.h>
#include <conio.h>
#include <graphics.h>
#include <dos.h>

int sign(float args)
{
    if (args < 0)
        return -1;
    else if (args > 0)
        return 1;
    else return 0;
}

void main()
{
    int gd = DETECT, gm;
    initgraph(&gd, &gm, "C:\\turboc3\\bgi");
	
    int x, y, x1, y1;
    float l, dx, dy, xinc, yinc;
	
    cout << "Enter starting co ordinates (x, y): ";
    cin >> x >> y;
    cout << "Enter ending co ordinates (x, y): ";
    cin >> x1 >> y1;
	
    // Set length as x1-x or y1-y, whatever is greater
    l = abs(x1 - x) > abs(y1 - y) ? abs (x1 - x) : abs (y1 - y);
	
    // Calculate delta(x) and delta(y)
    dx = (x1 - x)/l;
    dy = (y1 - y)/l;

    xinc = x + 0.5 * sign(dx);
    yinc = y + 0.5 * sign(dy);

    for (int i = 0; i <= l; i ++)
    {
        putpixel(abs(xinc), abs(yinc), WHITE);
        xinc = abs (xinc + dx);
        yinc = abs (yinc + dy);
    }
    
    getch();
    closegraph();
}