#include <iostream>
#include <GL/glut.h>
#include <cmath>

using namespace std;

void display(int x1, int y1, int x2, int y2) {
	glClearColor(0.0, 0.0, 0.0, 1.0);
	glClear(GL_COLOR_BUFFER_BIT);
	glColor3f(1.0, 0.0, 0.0);
	glPointSize(2.0f);
	glBegin(GL_POINTS);
	int dx, dy, x, y, xend, p;
	int i = (int)(x1 + 0.5);
	int j = (int)(y1 + 0.5);
	int k = (int)(x2 + 0.5);
	int l = (int)(y2 + 0.5);	
	
	dx = abs(x1 - x2);
	dy = abs(y1 - y2);
	p = 2 * (dy - dx);
	 
	if (i > k) {
		x = k;
		y = l;
		xend = i;
	}else {
		x = i;
		y = j;
		xend = k;
	}
	glVertex2f(x, y);

	while (x < xend) {
		x += 1;
		if (p < 0) {
			p = p + 2*dy;
		}else {
			y = y + 1;
			p = p + 2*(dy - dx);
		}
		glVertex2f(x, y);
	}

	glEnd();
	glFlush();
}

int main(int argv,  char **argc) {
	glutInit(&argv, argc);
	glutInitDisplayMode(GLUT_SINGLE | GLUT_RGBA | GLUT_DEPTH);
	glutInitWindowPosition(0, 0);
	glutInitWindowSize(1367, 768);
	glutCreateWindow("line");
	glMatrixMode(GL_PROJECTION);
	gluOrtho2D(0, 1367, 0, 768);
	display(0.0, 0.0, 675, 550);
	glutMainLoop();

	return 0;
}