/*
 * Copyright (c) 1993-1997, 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 * Unpublished-- rights reserved under the copyright laws of the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(R) is a registered trademark of Silicon Graphics, Inc.
 */

/*
 *  alpha3D.c
 *  This program demonstrates how to intermix opaque and
 *  alpha blended polygons in the same scene, by using 
 *  glDepthMask.  Press the 'a' key to animate moving the 
 *  transparent object through the opaque object.  Press 
 *  the 'r' key to reset the scene.
 */
#include <stdlib.h>
#include <stdio.h>
#include <GL/glut.h>

#define MAXZ 8.0
#define MINZ -8.0
#define ZINC 4.

static float solidZ = MAXZ;
static float transparentZ = MINZ;
static GLuint sphereList, cubeList;

static void init(void)
{
   GLfloat mat_specular[] = { 1.0, 1.0, 1.0, 0.15 };
   GLfloat mat_shininess[] = { 100.0 };
   GLfloat position[] = { 0.5, 0.5, 1.0, 0.0 };

   glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);
   glMaterialfv(GL_FRONT, GL_SHININESS, mat_shininess);
   glLightfv(GL_LIGHT0, GL_POSITION, position);

   glEnable(GL_LIGHTING);
   glEnable(GL_LIGHT0);
   glEnable(GL_DEPTH_TEST);

   sphereList = glGenLists(1);
   glNewList(sphereList, GL_COMPILE);
      glutSolidSphere (0.4, 16, 16);
   glEndList();

   cubeList = glGenLists(1);
   glNewList(cubeList, GL_COMPILE);
      glutSolidCube (0.6);
   glEndList();
}

static void display(void)
{
   GLfloat mat_solid[] = { 0.75, 0.75, 0.0, 1.0 };
   GLfloat mat_zero[] = { 0.0, 0.0, 0.0, 1.0 };
   GLfloat mat_transparent[] = { 0.0, 0.8, 0.8, 0.6 };
   GLfloat mat_emission[] = { 0.0, 0.3, 0.3, 0.6 };

   glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

   glPushMatrix ();
      glTranslatef (-0.15, -0.15, solidZ);
      glMaterialfv(GL_FRONT, GL_EMISSION, mat_zero);
      glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_solid);
      glCallList (sphereList);
   glPopMatrix ();

   glPushMatrix ();
      glTranslatef (0.15, 0.15, transparentZ);
      glRotatef (15.0, 1.0, 1.0, 0.0);
      glRotatef (30.0, 0.0, 1.0, 0.0);
      glMaterialfv(GL_FRONT, GL_EMISSION, mat_emission);
      glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_transparent);
      glEnable (GL_BLEND);
      glDepthMask (GL_FALSE);
      glBlendFunc (GL_SRC_ALPHA, GL_ONE);
      glCallList (cubeList);
      glDepthMask (GL_TRUE);
      glDisable (GL_BLEND);
   glPopMatrix ();

   glutSwapBuffers();
}

static void reshape(int w, int h)
{
   glViewport(0, 0, (GLint) w, (GLint) h);
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   if (w <= h)
      glOrtho (-1.5, 1.5, -1.5*(GLfloat)h/(GLfloat)w,
               1.5*(GLfloat)h/(GLfloat)w, -10.0, 10.0);
   else
      glOrtho (-1.5*(GLfloat)w/(GLfloat)h,
               1.5*(GLfloat)w/(GLfloat)h, -1.5, 1.5, -10.0, 10.0);
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();
}

static void animate(void)
{
   static double t0 = -1.;
   if (solidZ <= MINZ || transparentZ >= MAXZ)
   {
      glutIdleFunc(NULL);
      t0 = -1.;
   }
   else {
      double t, dt;
      t = glutGet(GLUT_ELAPSED_TIME) / 1000.;
      if (t0 < 0.)
         t0 = t;
      dt = t - t0;
      t0 = t;
      solidZ -= ZINC*dt;
      transparentZ += ZINC*dt;
      glutPostRedisplay();
   }
}

/* ARGSUSED1 */
static void keyboard(unsigned char key, int x, int y)
{
   switch (key) {
      case 'a':
      case 'A':
         solidZ = MAXZ;
         transparentZ = MINZ;
         glutIdleFunc(animate);
         break;
      case 'r':
      case 'R':
         solidZ = MAXZ;
         transparentZ = MINZ;
         glutPostRedisplay();
         break;
      case 27:
        exit(0);
    }
}

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