OpenGLUT 0.6.3 development - OpenGLUT: feedback.c File Reference
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# feedback.c File Reference

## Detailed Description

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.

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     * Unpublished-- rights reserved under the copyright laws of the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

    #include <GL/openglut.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);

       glFinish();
    }

    /* ARGSUSED1 */
    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;
    }

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