Appendix D. Example OpenGL Program With the GLUT Library
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## Appendix D. Example OpenGL Program With the GLUT Library

This program uses OpenGL and the GLUT library to display a planet rotating around the sun. It demonstrates how to composite modeling transformations to draw translated and rotated models. Pressing the left, right, up, and down arrow keys alters the rotation of the planet around the sun.

    /*
     *  planet.c
     *  This program shows how to composite modeling transformations
     *  to draw translated and rotated models.
     *  Interaction:  pressing the d and y keys (day and year)
     *  alters the rotation of the planet around the sun.
     */
    #include <GL/glut.h>
    #include <stdlib.h>

    static int year = 0, day = 0;

    void init(void)
    {
       glClearColor(0.0, 0.0, 0.0, 0.0);
       glShadeModel(GL_FLAT);
    }

    void display(void)
    {
       glClear(GL_COLOR_BUFFER_BIT);
       glColor3f(1.0, 1.0, 1.0);

       glPushMatrix();
       glutWireSphere(1.0, 20, 16);   /* draw sun */
       glRotatef((GLfloat)year, 0.0, 1.0, 0.0);
       glTranslatef(2.0, 0.0, 0.0);
       glRotatef((GLfloat)day, 0.0, 1.0, 0.0);
       glutWireSphere(0.2, 10, 8);    /* draw smaller planet */
       glPopMatrix();
       glutSwapBuffers();
    }

    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, 20.0);
       glMatrixMode(GL_MODELVIEW);
       glLoadIdentity();
       gluLookAt(0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
    }

    /* ARGSUSED1 */
    void keyboard (unsigned char key, int x, int y)
    {
       switch (key) {
          case 'd':
             day = (day + 10) % 360;
             glutPostRedisplay();
             break;
          case 'D':
             day = (day - 10) % 360;
             glutPostRedisplay();
             break;
          case 'y':
             year = (year + 5) % 360;
             glutPostRedisplay();
             break;
          case 'Y':
             year = (year - 5) % 360;
             glutPostRedisplay();
             break;
          case 27:
             exit(0);
             break;
          default:
             break;
       }
    }

    int main(int argc, char **argv)
    {
       glutInit(&argc, argv);
       glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB);
       glutInitWindowSize(500, 500);
       glutInitWindowPosition(100, 100);
       glutCreateWindow(argv[0]);
       init();
       glutDisplayFunc(display);
       glutReshapeFunc(reshape);
       glutKeyboardFunc(keyboard);
       glutMainLoop();
       return 0;
    }

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Appendix C. OpenGL Names, Types, and Error |  | Appendix E. Example Program Using Xt and a WorkProc