openGL - glortho()

glortho() 함수는 화면상의 좌표축을 설정하는 함수이다.

#include "windows.h"
#include "GL/gl.h"
#include "GL/glut.h"

void display(void)
{
/*  clear all pixels  */
    glClear (GL_COLOR_BUFFER_BIT);
/*  draw white polygon (rectangle) with corners at
 *  (0.25, 0.25, 0.0) and (0.75, 0.75, 0.0)  
 */
    glColor3f (1.0, 1.0, 1.0);
    glBegin(GL_POLYGON);
        glVertex3f (0.25, 0.25, 0.0);
        glVertex3f (0.75, 0.25, 0.0);
        glVertex3f (0.75, 0.75, 0.0);
        glVertex3f (0.25, 0.75, 0.0);
    glEnd();
/*  don’t wait!  
 *  start processing buffered OpenGL routines 
 */
    glFlush ();
}
void init (void) 
{
/*  select clearing (background) color       */
    glClearColor (0.0, 0.0, 0.0, 0.0);
/*  initialize viewing values  */
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0);
}
/* 
 *  Declare initial window size, position, and display mode
 *  (single buffer and RGBA).  Open window with "hello"
 *  in its title bar.  Call initialization routines.
 *  Register callback function to display graphics.
 *  Enter main loop and process events.
 */
int main(int argc, char** argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize (250, 250); 
    glutInitWindowPosition (100, 100);
    glutCreateWindow ("hello");
    init ();
    glutDisplayFunc(display);
    glutMainLoop();
    return 0;   /* ISO C requires main to return int. */
}

glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0); 로 설정할 경우의 결과

glOrtho(0.0, 2.0, 0.0, 2.0, -2.0, 2.0); 로 설정할 경우의 결과

대충 정리하자면, 아래 그림과 같다고 할까나~?!

[링크 : http://www.opengl.org/sdk/docs/man/xhtml/glOrtho.xml]