OpenGL: Bresenham's Line Drawing Algorithm Implementation - c++

Question

I've been trying to generate a line using Bresenham's Algorithm (Yes, I know in built functions exist, but this is something I've been asked to implement) using the following code.
But for some reason, I am not being able to see the line on the window. I just get an empty window.
I initially tried drawing points with SetPixel() but I was short of 2 arguments(HDC and COLORREF) apart from just the X and Y coordinates. I don't know what the other 2 arguments do, so I had to try something else.
So I used a solution I found here on StackOverflow to generate the point. Though I do not get any compilation error or warnings, the code just doesn't seem to work. How about you try looking for the problem:
#include<iostream>
#include<GL/glut.h>
#include<stdlib.h>
#include<math.h>
using namespace std;
int x00;
int y00;
int xEnd;
int yEnd;
void init(){
glClearColor(1,0,0,0);
glMatrixMode( GL_PROJECTION );
gluOrtho2D(0,500,0,500);
}
void bres()
{
int dx = fabs(xEnd - x00), dy = fabs(yEnd - y00);
int p = 2*dy-dx;
int x, y;
if(x00>xEnd){
x=xEnd;
y=yEnd;
xEnd=x00;
}
else{
x=x00;
y=y00;
}
//Stack Overflow Solution to generate a point:
glBegin(GL_POINTS);
glColor3f(0,0,0);
glVertex2i(x,y);
glEnd();
while(x<xEnd){
x++;
if(p<0){
p = p + 2*dy;
}
else{
y++;
p= p + 2*dy - 2*dx;
}
glBegin(GL_POINTS);
glColor3f(0,0,0);
glVertex2i(x,y);
glEnd();
}
}
void display()
{
glClear(GL_COLOR_BUFFER_BIT);
bres();
glFlush();
}
int main(int argc, char* argv[])
{
cout<<"Enter the co ordinates for 2 points: ";
cin>>x00>>y00>>xEnd>>yEnd;
glutInit(&argc, argv);
glutInitWindowSize(600,600);
glutInitWindowPosition(10,10);
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
glutCreateWindow("Bresenham's Algo");
init();
glutDisplayFunc(display);
glutMainLoop();
return 0;
}

Answer 1

Since you are using a double buffered window
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
you have to call glutSwapBuffers instead of glFlush.
If you would use a single buffered window
glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE | GLUT_DEPTH);
then glFlush would work.
Change your code somehow like this:
void display()
{
glClear(GL_COLOR_BUFFER_BIT);
bres();
//glFlush();
glutSwapBuffers();
}