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+
+/* Copyright (c) Mark J. Kilgard, 1994. */
+
+/**
+ * (c) Copyright 1993, Silicon Graphics, Inc.
+ * ALL RIGHTS RESERVED 
+ * Permission to use, copy, modify, and distribute this software for 
+ * any purpose and without fee is hereby granted, provided that the above
+ * copyright notice appear in all copies and that both the copyright notice
+ * and this permission notice appear in supporting documentation, and that 
+ * the name of Silicon Graphics, Inc. not be used in advertising
+ * or publicity pertaining to distribution of the software without specific,
+ * written prior permission. 
+ *
+ * THE MATERIAL EMBODIED ON THIS SOFTWARE IS PROVIDED TO YOU "AS-IS"
+ * AND WITHOUT WARRANTY OF ANY KIND, EXPRESS, IMPLIED OR OTHERWISE,
+ * INCLUDING WITHOUT LIMITATION, ANY WARRANTY OF MERCHANTABILITY OR
+ * FITNESS FOR A PARTICULAR PURPOSE.  IN NO EVENT SHALL SILICON
+ * GRAPHICS, INC.  BE LIABLE TO YOU OR ANYONE ELSE FOR ANY DIRECT,
+ * SPECIAL, INCIDENTAL, INDIRECT OR CONSEQUENTIAL DAMAGES OF ANY
+ * KIND, OR ANY DAMAGES WHATSOEVER, INCLUDING WITHOUT LIMITATION,
+ * LOSS OF PROFIT, LOSS OF USE, SAVINGS OR REVENUE, OR THE CLAIMS OF
+ * THIRD PARTIES, WHETHER OR NOT SILICON GRAPHICS, INC.  HAS BEEN
+ * ADVISED OF THE POSSIBILITY OF SUCH LOSS, HOWEVER CAUSED AND ON
+ * ANY THEORY OF LIABILITY, ARISING OUT OF OR IN CONNECTION WITH THE
+ * POSSESSION, USE OR PERFORMANCE OF THIS SOFTWARE.
+ * 
+ * US Government Users Restricted Rights 
+ * Use, duplication, or disclosure by the Government is subject to
+ * restrictions set forth in FAR 52.227.19(c)(2) or subparagraph
+ * (c)(1)(ii) of the Rights in Technical Data and Computer Software
+ * clause at DFARS 252.227-7013 and/or in similar or successor
+ * clauses in the FAR or the DOD or NASA FAR Supplement.
+ * Unpublished-- rights reserved under the copyright laws of the
+ * United States.  Contractor/manufacturer is Silicon Graphics,
+ * Inc., 2011 N.  Shoreline Blvd., Mountain View, CA 94039-7311.
+ *
+ * OpenGL(TM) is a trademark of Silicon Graphics, Inc.
+ */
+/*
+ *  fog.c
+ *  This program draws 5 red teapots, each at a different 
+ *  z distance from the eye, in different types of fog.  
+ *  Pressing the left mouse button chooses between 3 types of 
+ *  fog:  exponential, exponential squared, and linear.  
+ *  In this program, there is a fixed density value, as well 
+ *  as fixed start and end values for the linear fog.
+ */
+#include <stdlib.h>
+#include <math.h>
+#include <GL/glut.h>
+
+GLint fogMode;
+
+void 
+selectFog(int mode)
+{
+    switch(mode) {
+    case GL_LINEAR:
+        glFogf(GL_FOG_START, 1.0);
+        glFogf(GL_FOG_END, 5.0);
+	/* falls through */
+    case GL_EXP2:
+    case GL_EXP:
+        glFogi(GL_FOG_MODE, mode);
+	glutPostRedisplay();
+	break;
+    case 0:
+	exit(0);
+    }
+}
+
+/*  Initialize z-buffer, projection matrix, light source, 
+ *  and lighting model.  Do not specify a material property here.
+ */
+void 
+myinit(void)
+{
+    GLfloat position[] =
+    {0.0, 3.0, 3.0, 0.0};
+    GLfloat local_view[] =
+    {0.0};
+
+    glEnable(GL_DEPTH_TEST);
+    glDepthFunc(GL_LESS);
+
+    glLightfv(GL_LIGHT0, GL_POSITION, position);
+    glLightModelfv(GL_LIGHT_MODEL_LOCAL_VIEWER, local_view);
+
+    glFrontFace(GL_CW);
+    glEnable(GL_LIGHTING);
+    glEnable(GL_LIGHT0);
+    glEnable(GL_AUTO_NORMAL);
+    glEnable(GL_NORMALIZE);
+    glEnable(GL_FOG);
+    {
+        GLfloat fogColor[4] =
+        {0.5, 0.5, 0.5, 1.0};
+
+        fogMode = GL_EXP;
+        glFogi(GL_FOG_MODE, fogMode);
+        glFogfv(GL_FOG_COLOR, fogColor);
+        glFogf(GL_FOG_DENSITY, 0.35);
+        glHint(GL_FOG_HINT, GL_DONT_CARE);
+        glClearColor(0.5, 0.5, 0.5, 1.0);
+    }
+}
+
+void 
+renderRedTeapot(GLfloat x, GLfloat y, GLfloat z)
+{
+    float mat[4];
+
+    glPushMatrix();
+    glTranslatef(x, y, z);
+    mat[0] = 0.1745;
+    mat[1] = 0.01175;
+    mat[2] = 0.01175;
+    mat[3] = 1.0;
+    glMaterialfv(GL_FRONT, GL_AMBIENT, mat);
+    mat[0] = 0.61424;
+    mat[1] = 0.04136;
+    mat[2] = 0.04136;
+    glMaterialfv(GL_FRONT, GL_DIFFUSE, mat);
+    mat[0] = 0.727811;
+    mat[1] = 0.626959;
+    mat[2] = 0.626959;
+    glMaterialfv(GL_FRONT, GL_SPECULAR, mat);
+    glMaterialf(GL_FRONT, GL_SHININESS, 0.6 * 128.0);
+    glutSolidTeapot(1.0);
+    glPopMatrix();
+}
+
+/*  display() draws 5 teapots at different z positions.
+ */
+void 
+display(void)
+{
+    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
+    renderRedTeapot(-4.0, -0.5, -1.0);
+    renderRedTeapot(-2.0, -0.5, -2.0);
+    renderRedTeapot(0.0, -0.5, -3.0);
+    renderRedTeapot(2.0, -0.5, -4.0);
+    renderRedTeapot(4.0, -0.5, -5.0);
+    glFlush();
+}
+
+void 
+myReshape(int w, int h)
+{
+    glViewport(0, 0, w, h);
+    glMatrixMode(GL_PROJECTION);
+    glLoadIdentity();
+    if (w <= (h * 3))
+        glOrtho(-6.0, 6.0, -2.0 * ((GLfloat) h * 3) / (GLfloat) w,
+            2.0 * ((GLfloat) h * 3) / (GLfloat) w, 0.0, 10.0);
+    else
+        glOrtho(-6.0 * (GLfloat) w / ((GLfloat) h * 3),
+            6.0 * (GLfloat) w / ((GLfloat) h * 3), -2.0, 2.0, 0.0, 10.0);
+    glMatrixMode(GL_MODELVIEW);
+    glLoadIdentity();
+}
+
+/*  Main Loop
+ *  Open window with initial window size, title bar, 
+ *  RGBA display mode, depth buffer, and handle input events.
+ */
+int 
+main(int argc, char **argv)
+{
+    glutInit(&argc, argv);
+    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
+    glutInitWindowSize(450, 150);
+    glutCreateWindow(argv[0]);
+    myinit();
+    glutReshapeFunc(myReshape);
+    glutDisplayFunc(display);
+    glutCreateMenu(selectFog);
+    glutAddMenuEntry("Fog EXP", GL_EXP);
+    glutAddMenuEntry("Fog EXP2", GL_EXP2);
+    glutAddMenuEntry("Fog LINEAR", GL_LINEAR);
+    glutAddMenuEntry("Quit", 0);
+    glutAttachMenu(GLUT_RIGHT_BUTTON);
+    glutMainLoop();
+    return 0;             /* ANSI C requires main to return int. */
+}