feedback.c

/*
 * 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 * Unpublished-- rights reserved under the copyright laws of the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.
 */

/*
 * feedback.c
 * This program demonstrates use of OpenGL feedback.  First,
 * a lighting environment is set up and a few lines are drawn.
 * Then feedback mode is entered, and the same lines are 
 * drawn.  The results in the feedback buffer are printed.
 */
#include <GL/glut.h>
#include <stdlib.h>
#include <stdio.h>

/*  Initialize lighting.
 */
void init(void)
{
   glEnable(GL_LIGHTING);
   glEnable(GL_LIGHT0);
}

/* Draw a few lines and two points, one of which will 
 * be clipped.  If in feedback mode, a passthrough token 
 * is issued between the each primitive.
 */
void drawGeometry (GLenum mode)
{
   glBegin (GL_LINE_STRIP);
   glNormal3f (0.0, 0.0, 1.0);
   glVertex3f (30.0, 30.0, 0.0);
   glVertex3f (50.0, 60.0, 0.0);
   glVertex3f (70.0, 40.0, 0.0);
   glEnd ();
   if (mode == GL_FEEDBACK)
      glPassThrough (1.0);
   glBegin (GL_POINTS);
   glVertex3f (-100.0, -100.0, -100.0);  /*  will be clipped  */
   glEnd ();
   if (mode == GL_FEEDBACK)
      glPassThrough (2.0);
   glBegin (GL_POINTS);
   glNormal3f (0.0, 0.0, 1.0);
   glVertex3f (50.0, 50.0, 0.0);
   glEnd ();
}

/* Write contents of one vertex to stdout.	*/
void print3DcolorVertex (GLint size, GLint *count, 
                         GLfloat *buffer)
{
   int i;

   printf ("  ");
   for (i = 0; i < 7; i++) {
      printf ("%4.2f ", buffer[size-(*count)]);
      *count = *count - 1;
   }
   printf ("\n");
}

/*  Write contents of entire buffer.  (Parse tokens!)	*/
void printBuffer(GLint size, GLfloat *buffer)
{
   GLint count;
   GLfloat token;

   count = size;
   while (count) {
      token = buffer[size-count]; count--;
      if (token == GL_PASS_THROUGH_TOKEN) {
         printf ("GL_PASS_THROUGH_TOKEN\n");
         printf ("  %4.2f\n", buffer[size-count]);
         count--;
      }
      else if (token == GL_POINT_TOKEN) {
         printf ("GL_POINT_TOKEN\n");
         print3DcolorVertex (size, &count, buffer);
      }
      else if (token == GL_LINE_TOKEN) {
         printf ("GL_LINE_TOKEN\n");
         print3DcolorVertex (size, &count, buffer);
         print3DcolorVertex (size, &count, buffer);
      }
      else if (token == GL_LINE_RESET_TOKEN) {
         printf ("GL_LINE_RESET_TOKEN\n");
         print3DcolorVertex (size, &count, buffer);
         print3DcolorVertex (size, &count, buffer);
      }
   }
}

void display(void)
{
   GLfloat feedBuffer[1024];
   GLint size;

   glMatrixMode (GL_PROJECTION);
   glLoadIdentity ();
   glOrtho (0.0, 100.0, 0.0, 100.0, 0.0, 1.0);

   glClearColor (0.0, 0.0, 0.0, 0.0);
   glClear(GL_COLOR_BUFFER_BIT);
   drawGeometry (GL_RENDER);

   glFeedbackBuffer (1024, GL_3D_COLOR, feedBuffer);
   (void) glRenderMode (GL_FEEDBACK);
   drawGeometry (GL_FEEDBACK);

   size = glRenderMode (GL_RENDER);
   printBuffer (size, feedBuffer);
}

void keyboard(unsigned char key, int x, int y)
{
   switch (key) {
      case 27:
         exit(0);
         break;
   }
}

/*  Main Loop  */
int main(int argc, char** argv)
{
   glutInit(&argc, argv);
   glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
   glutInitWindowSize (100, 100);
   glutInitWindowPosition (100, 100);
   glutCreateWindow(argv[0]);
   init();
   glutDisplayFunc(display);
   glutKeyboardFunc (keyboard);
   glutMainLoop();
   return 0; 
}