Dashed Line Generation (DDA) using OpenGL – Program Source Code

#include <GL/glut.h>
#include<stdio.h>
#include<stdlib.h>
#include<math.h>
int x1,x2,y1,y2;
float gap;
void display(void)
 {
int DelX,DelY,Max;
 int n=0,Total=1,j=0;
 double Sigma=1,XIncr,YIncr,x,y,slope;
 double gapX,gapY;
 glClear (GL_COLOR_BUFFER_BIT);
 glColor3f (1.0, 0.0, 0.0);
 if(x2<x1 && y2<y1)
 {
 int var;
 var=x1; x1=x2; x2=var;
 var=y1; y1=y2; y2=var;
 }
 DelX = x2 - x1;
 DelY = y2 - y1; 
 Max = ((DelX > DelY) ? DelX:DelY); 

 for( n=0 ; Total<=Max ; n++)
 {
 Total=Total*2;
 }
 for( int i=n ; i>0 ; i--)
 {
 Sigma = Sigma/2;
 }
 XIncr = Sigma*DelX;
 YIncr = Sigma*DelY; 
 x=x1; y=y1;

 glBegin(GL_POINTS);
 glVertex2s(x1,y1);
 slope = DelY/DelX; 
 gapX = gap/sqrt(1+slope*slope);
 // gapX = gap/.5;
 while(x!=x2 || y!=y2)
 {
 x = x+XIncr;
 y = y+YIncr;
 j = x/gapX;

 if((j%2)==0)
 {
 glVertex2s(x,y);
 printf("%lf %lf\n ",x,y);
 }
 } 
 glColor3f (1.0, 1.0, 1.0);
 for(int i=-100 ; i<=100 ; i++)
 {
 glVertex2s(i,0);
 glVertex2s(0,i);
 } 
 for(int i=-2; i<=2 ; i++)
 {
 glVertex2s(95+i,4+i);
 glVertex2s(95-i,4+i);
 } 
 for(int i=0; i<=2 ; i++)
 {
 glVertex2s(4+i,95+i);
 glVertex2s(4-i,95+i);
 glVertex2s(4,95-i);
 } 
 glEnd();
 glFlush();
}
 void init(void) 
 {
 glClearColor (0.0, 0.0, 0.0, 0.0);
 glOrtho(-100.0, 100.0, -100.0, 100.0, -1.0, 1.0);
 }
int main(int argc, char **argv)
 { 
 printf("Enter Initial points:\n"); 
 scanf("%d%d", &x1 , & y1);
 printf("Enter Final points:\n");
 scanf("%d%d", &x2 , & y2);
 printf("Enter Gapping:\n");
 scanf("%f", &gap); 

 glutInit(&argc, argv);
 glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
 glutInitWindowSize (500, 500); 
 glutInitWindowPosition (100, 100);
 glutCreateWindow ("DDA");
 init ();
 glutDisplayFunc(display);
 glutMainLoop ();
 return 0;
 }

OUTPUT: