outdated: 1.1LineSegment

#include <windows.h>
#include <gl/glew.h>
#include <gl/glut.h>
#include <cstdio>
#include <cstdlib>
#include <cmath>

void Init(void)
{
    glClearColor(1.0, 1.0, 1.0, 0.0);  // Set display-window color to white
    // Drawing two-dimensional graphics is a special case of rendering 3D graphics 
    // The two dimensional matrix of the world coordinate system is projected onto the screen. 
    glMatrixMode(GL_PROJECTION);
    gluOrtho2D(0.0, 200.0, 0.0, 150.0);

}

void lineSegment(void)
{
    // glClearColor() does not allow the display window appears on the screen
    // GlClear function allows assignment of the window to appear on the screen 
    glClear(GL_COLOR_BUFFER_BIT);    // Clear displaye window
    
    glColor3f(1.0, 0.0, 0.0);        // Display the color of the window object 
    glBegin(GL_LINES);               // GL_POINTS GL_LINES GL_LINE_STRIP GL_LINE_LOOP
    glVertex2i(180, 15);             // Specify line_segment geometry
    glVertex2i(10, 145);
    glEnd();

    glFlush();                       // Process all OpenGL rountines as quickly as possible
}

int main(int argc, char* argv[])
{
    glutInit(&argc, argv);                 // Initialize GLUT
                                           // Set the cache and color model of the display window, and so on
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);   
    glutInitWindowPosition(50, 100);  // Display the location of the specified pixel 
    glutInitWindowSize(400, 300);     // Set the initial width and height of the display window
    glutCreateWindow("An Example OpenGL Program");      // Title
    
    Init();
    // LineSegment for the creation of the graph, 
    // passed to the function, and the graph is assigned to the display window
    glutDisplayFunc(lineSegment);  // Display callback function
    // The original display window has not yet appeared on the screen, 
    // glutMainLoop () will display the window and its content activation, and must be the last function 
    glutMainLoop();
    return 0;
}