OpenGL question

First, lets get the problem out of the way.

Code:

---

Draw an octahedron [eight triangles] in space with corners at (+/-1.0, 0.0, +/-1.0) and (0.0, +/-1.0, 0.0).
Use a 3D perspective frame (viewing volume) with boundaries (+/-5.0, +/-5.0, +/-5.0).
Temporarily assign each face different color, display and rotate around the y-axis.

---

Now, I am new to OpenGL, and really, new to C++ all together, so I am learning at a slow pace. Disclaimer aside, I am still tweaking the octahedron because it isn't coming out the way I am expecting and I still have to figure out what I am missing, but that is not the issue right now. You will see that I am using an old program I did which turned out to be a simple box with all its sides, and a cut open area revealing the inner sides as well. I have removed the code I didn't feel needed to be used in this assignment and have tried moving on, while hitting some roadblocks.

The main issue that I am having, is that I have no idea how I am supposed to be able to display the octahedron, and have it rotate around the y-axis. I can't really conceive anyway of how I am going to do this nor do I truly have the knowledge of going about doing it. Any helpful tips or hints would be greatly appreciated. I will show you what I have so far (the busted octahedron as of now).

Code:

---

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <GL/glut.h>

typedef float Point2f [2];

GLfloat v [6][3] = {{-1.0, 0.0, -1.0}, {1.0, 0.0, -1.0},
                                {-1.0, 0.0, 1.0}, {1.0, 0.0, 1.0},
                                {0.0, 1.0, 0.0}, {0.0, -1.0, 0.0}};

GLfloat colors [6][3] = {{0.0, 0.0, 0.0}, {1.0, 0.0, 0.0},
                                        {0.0, 1.0, 0.0}, {0.0, 0.0, 1.0},
                                        {1.0, 0.0, 1.0}, {0.0, 1.0, 1.0}};

void side (GLfloat * a, GLfloat * b, GLfloat * c, GLfloat * d) {
        glVertex3fv (a);
        glVertex3fv (b);
        glVertex3fv (c);
//        glVertex3fv (d);
}

void octo (GLfloat * a, GLfloat * b, GLfloat * c, GLfloat * d,
                  GLfloat * e, GLfloat * f, GLfloat * g, GLfloat * h) {
        glColor3fv (colors [0]);
        side (a, b, d, c);
        glColor3fv (colors [1]);
        side (c, d, f, e);       
        glColor3fv (colors [2]);
        side (e, f, h, g);
        glColor3fv (colors [3]);
        side (g, h, b, a);
        glColor3fv (colors [4]);
        side (a, c, e, g);
        glColor3fv (colors [5]);
        side (b, d, f, h);
}

void display ( ) {                // need one such function per callback method
        char * name = "octahedron";

        glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
       
        glPushMatrix ( );
        glBegin (GL_TRIANGLE_STRIP);
                octo (v [0], v [1], v [2], v [3], v [4], v[5], v[6], v[7]);
        glEnd ( );
        glPopMatrix ( );

        glFlush ( );
}

void myReshape (int w, int h) {
        GLfloat aspect;

        glViewport (0, 0, w, h);
        glMatrixMode (GL_PROJECTION);
        glLoadIdentity ( );
        aspect = (GLfloat) h / (GLfloat) w;
        glOrtho (-5.0, 5.0, -5.0, 5.0, -5.0, 5.0);

        gluPerspective (10.0, aspect, 10.0, -10.0);                                                       

        gluLookAt (5.0, 5.0, 10.0, 0.5, 1.0, 1.0, 0.0, 1.0, 0.0);                       
        glMatrixMode (GL_MODELVIEW);
        glutPostRedisplay ( );
}

int main (int argc, char ** argv) {

        /* 3D initialization stuff */
        glutInit (&argc, argv);
        glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);       
        glutInitWindowSize (500, 500);
        glutInitWindowPosition (100,100);
        glutCreateWindow ("Octahedron");
        glutReshapeFunc (myReshape);
        glutDisplayFunc (display);                /* display callback invoked when window opened */
        glEnable (GL_DEPTH_TEST);
        glClearColor (1.0, 1.0, 1.0, 1.0);        /* white background */

        glutMainLoop ( );
        return 0;
}

---

Thanks again.

Read, learn, solve your problem.

thanks for this site, some very informative stuff :)

If you are still stuck after going through this, you may want to go ask your question at an OpenGL forum (OpenGL.org Discussion and Help Forums - Powered by UBB.threads™ is an example).

Have a look at glRotatef() for rotation. You'll need to keep track of a rotation amount and increment it before each rendering.