OpenGL画四个三角形组成四面体，并进行旋转

#define GLUT_DISABLE_ATEXIT_HACK
#include <GL/glut.h>
#include <stdlib.h>
#include <stdio.h>

static float roangles;

void init(void)
{
    glClearColor (0.0, 0.0, 0.0, 0.0);
    glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
    glEnable(GL_DEPTH_TEST);

}

void display(void)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glPushMatrix();

    glRotatef( roangles, 0.0, 1.0, 0.0 );
    glBegin(GL_TRIANGLES);
    glVertex3f(1.0, 0.0, 0.0);
    glVertex3f(0.0, 1.0, 0.0);
    glVertex3f(0.0, 0.0, 1.0);

    glVertex3f(0.0, 0.0, 0.0);
    glVertex3f(0.0, 1.0, 0.0);
    glVertex3f(1.0, 0.0, 0.0);

    glVertex3f(0.0, 0.0, 0.0);
    glVertex3f(0.0, 0.0, 1.0);
    glVertex3f(0.0, 1.0, 0.0);

    glVertex3f(0.0, 0.0, 0.0);
    glVertex3f(0.0, 0.0, 1.0);
    glVertex3f(1.0, 0.0, 0.0);

    glEnd();
    glPopMatrix();
    glFlush();
}

void reshape(int w, int h)
{
    glViewport(0, 0, (GLsizei) w, (GLsizei) h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(60.0, (GLfloat) w/(GLfloat) h, 1.0, 30.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glTranslatef(0.0, 0.0, -3.6);
    glRotatef( 45, 1.0, 0.0, 0.0 );
}
void idle()
{
    roangles += 0.01f;
    glutPostRedisplay();
}
/* ARGSUSED1 */
void keyboard(unsigned char key, int x, int y)
{
    switch (key) {
    case 27:
        exit(0);
        break;
    }
}

int main(int argc, char** argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
    glutInitWindowSize(250, 250);
    glutInitWindowPosition(100, 100);
    glutCreateWindow(argv[0]);
    glutIdleFunc( idle );
    init();
    glutReshapeFunc(reshape);
    glutDisplayFunc(display);
    glutKeyboardFunc (keyboard);
    glutMainLoop();
    return 0;
}