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

## Detailed Description

This is an illustration of the selection mode and name stack, which detects whether objects which collide with a viewing volume.

First, four triangles and a rectangular box representing a viewing volume are drawn (drawScene routine). The green triangle and yellow triangles appear to lie within the viewing volume, but the red triangle appears to lie outside it.

Then the selection mode is entered (selectObjects routine).

Drawing to the screen ceases. To see if any collisions occur, the four triangles are called. In this example, the green triangle causes one hit with the name 1, and the yellow triangles cause one hit with the name 3.

    /*
     * 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>

    /* draw a triangle with vertices at (x1, y1), (x2, y2)
     * and (x3, y3) at z units away from the origin.
     */
    void drawTriangle (GLfloat x1, GLfloat y1, GLfloat x2,
        GLfloat y2, GLfloat x3, GLfloat y3, GLfloat z)
    {
       glBegin (GL_TRIANGLES);
       glVertex3f (x1, y1, z);
       glVertex3f (x2, y2, z);
       glVertex3f (x3, y3, z);
       glEnd ();
    }

    /* draw a rectangular box with these outer x, y, and z values */
    void drawViewVolume (GLfloat x1, GLfloat x2, GLfloat y1,
                         GLfloat y2, GLfloat z1, GLfloat z2)
    {
       glColor3f (1.0, 1.0, 1.0);
       glBegin (GL_LINE_LOOP);
       glVertex3f (x1, y1, -z1);
       glVertex3f (x2, y1, -z1);
       glVertex3f (x2, y2, -z1);
       glVertex3f (x1, y2, -z1);
       glEnd ();

       glBegin (GL_LINE_LOOP);
       glVertex3f (x1, y1, -z2);
       glVertex3f (x2, y1, -z2);
       glVertex3f (x2, y2, -z2);
       glVertex3f (x1, y2, -z2);
       glEnd ();

       glBegin (GL_LINES);  /*  4 lines */
       glVertex3f (x1, y1, -z1);
       glVertex3f (x1, y1, -z2);
       glVertex3f (x1, y2, -z1);
       glVertex3f (x1, y2, -z2);
       glVertex3f (x2, y1, -z1);
       glVertex3f (x2, y1, -z2);
       glVertex3f (x2, y2, -z1);
       glVertex3f (x2, y2, -z2);
       glEnd ();
    }

    /* drawScene draws 4 triangles and a wire frame
     * which represents the viewing volume.
     */
    void drawScene (void)
    {
       glMatrixMode (GL_PROJECTION);
       glLoadIdentity ();
       gluPerspective (40.0, 4.0/3.0, 1.0, 100.0);

       glMatrixMode (GL_MODELVIEW);
       glLoadIdentity ();
       gluLookAt (7.5, 7.5, 12.5, 2.5, 2.5, -5.0, 0.0, 1.0, 0.0);
       glColor3f (0.0, 1.0, 0.0);   /*  green triangle  */
       drawTriangle (2.0, 2.0, 3.0, 2.0, 2.5, 3.0, -5.0);
       glColor3f (1.0, 0.0, 0.0);   /*  red triangle    */
       drawTriangle (2.0, 7.0, 3.0, 7.0, 2.5, 8.0, -5.0);
       glColor3f (1.0, 1.0, 0.0);   /*  yellow triangles    */
       drawTriangle (2.0, 2.0, 3.0, 2.0, 2.5, 3.0, 0.0);
       drawTriangle (2.0, 2.0, 3.0, 2.0, 2.5, 3.0, -10.0);
       drawViewVolume (0.0, 5.0, 0.0, 5.0, 0.0, 10.0);
    }

    /* processHits prints out the contents of the selection array
     */
    void processHits (GLint hits, GLuint buffer[])
    {
       GLint i;
       GLuint j, names, *ptr;

       printf ("hits = %d\n", hits);
       ptr = (GLuint *) buffer;
       for (i = 0; i < hits; i++) { /*  for each hit  */
          names = *ptr;
          printf (" number of names for hit = %d\n", names); ptr++;
          printf("  z1 is %g;", (float) *ptr/0x7fffffff); ptr++;
          printf(" z2 is %g\n", (float) *ptr/0x7fffffff); ptr++;
          printf ("   the name is ");
          for (j = 0; j < names; j++) { /*  for each name */
             printf ("%d ", *ptr); ptr++;
          }
          printf ("\n");
       }
    }

    /* selectObjects "draws" the triangles in selection mode,
     * assigning names for the triangles.  Note that the third
     * and fourth triangles share one name, so that if either
     * or both triangles intersects the viewing/clipping volume,
     * only one hit will be registered.
     */
    #define BUFSIZE 512

    void selectObjects(void)
    {
       GLuint selectBuf[BUFSIZE];
       GLint hits;

       glSelectBuffer (BUFSIZE, selectBuf);
       (void) glRenderMode (GL_SELECT);

       glInitNames();
       glPushName(0);

       glPushMatrix ();
       glMatrixMode (GL_PROJECTION);
       glLoadIdentity ();
       glOrtho (0.0, 5.0, 0.0, 5.0, 0.0, 10.0);
       glMatrixMode (GL_MODELVIEW);
       glLoadIdentity ();
       glLoadName(1);
       drawTriangle (2.0, 2.0, 3.0, 2.0, 2.5, 3.0, -5.0);
       glLoadName(2);
       drawTriangle (2.0, 7.0, 3.0, 7.0, 2.5, 8.0, -5.0);
       glLoadName(3);
       drawTriangle (2.0, 2.0, 3.0, 2.0, 2.5, 3.0, 0.0);
       drawTriangle (2.0, 2.0, 3.0, 2.0, 2.5, 3.0, -10.0);
       glPopMatrix ();
       glFlush ();

       hits = glRenderMode (GL_RENDER);
       processHits (hits, selectBuf);
    }

    void init (void)
    {
       glEnable(GL_DEPTH_TEST);
       glShadeModel(GL_FLAT);
    }

    void display(void)
    {
       glClearColor (0.0, 0.0, 0.0, 0.0);
       glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
       drawScene ();
       selectObjects ();
       glFlush();
    }

    /* 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 | GLUT_DEPTH);
       glutInitWindowSize (200, 200);
       glutInitWindowPosition (100, 100);
       glutCreateWindow (argv[0]);
       init();
       glutDisplayFunc(display);
       glutKeyboardFunc(keyboard);
       glutMainLoop();
       return 0;
    }

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