select.c revision 32001f49 
1/*
2 * Copyright (c) 1993-1997, Silicon Graphics, Inc.
3 * ALL RIGHTS RESERVED
4 * Permission to use, copy, modify, and distribute this software for
5 * any purpose and without fee is hereby granted, provided that the above
6 * copyright notice appear in all copies and that both the copyright notice
7 * and this permission notice appear in supporting documentation, and that
8 * the name of Silicon Graphics, Inc. not be used in advertising
9 * or publicity pertaining to distribution of the software without specific,
10 * written prior permission.
11 *
12 * THE MATERIAL EMBODIED ON THIS SOFTWARE IS PROVIDED TO YOU "AS-IS"
13 * AND WITHOUT WARRANTY OF ANY KIND, EXPRESS, IMPLIED OR OTHERWISE,
14 * INCLUDING WITHOUT LIMITATION, ANY WARRANTY OF MERCHANTABILITY OR
15 * FITNESS FOR A PARTICULAR PURPOSE.  IN NO EVENT SHALL SILICON
16 * GRAPHICS, INC.  BE LIABLE TO YOU OR ANYONE ELSE FOR ANY DIRECT,
17 * SPECIAL, INCIDENTAL, INDIRECT OR CONSEQUENTIAL DAMAGES OF ANY
18 * KIND, OR ANY DAMAGES WHATSOEVER, INCLUDING WITHOUT LIMITATION,
19 * LOSS OF PROFIT, LOSS OF USE, SAVINGS OR REVENUE, OR THE CLAIMS OF
20 * THIRD PARTIES, WHETHER OR NOT SILICON GRAPHICS, INC.  HAS BEEN
21 * ADVISED OF THE POSSIBILITY OF SUCH LOSS, HOWEVER CAUSED AND ON
22 * ANY THEORY OF LIABILITY, ARISING OUT OF OR IN CONNECTION WITH THE
23 * POSSESSION, USE OR PERFORMANCE OF THIS SOFTWARE.
24 *
25 * US Government Users Restricted Rights
26 * Use, duplication, or disclosure by the Government is subject to
27 * restrictions set forth in FAR 52.227.19(c)(2) or subparagraph
28 * (c)(1)(ii) of the Rights in Technical Data and Computer Software
29 * clause at DFARS 252.227-7013 and/or in similar or successor
30 * clauses in the FAR or the DOD or NASA FAR Supplement.
31 * Unpublished-- rights reserved under the copyright laws of the
32 * United States.  Contractor/manufacturer is Silicon Graphics,
33 * Inc., 2011 N.  Shoreline Blvd., Mountain View, CA 94039-7311.
34 *
35 * OpenGL(R) is a registered trademark of Silicon Graphics, Inc.
36 */
37
38/*
39 * select.c
40 * This is an illustration of the selection mode and
41 * name stack, which detects whether objects which collide
42 * with a viewing volume.  First, four triangles and a
43 * rectangular box representing a viewing volume are drawn
44 * (drawScene routine).  The green triangle and yellow
45 * triangles appear to lie within the viewing volume, but
46 * the red triangle appears to lie outside it.  Then the
47 * selection mode is entered (selectObjects routine).
48 * Drawing to the screen ceases.  To see if any collisions
49 * occur, the four triangles are called.  In this example,
50 * the green triangle causes one hit with the name 1, and
51 * the yellow triangles cause one hit with the name 3.
52 */
53#include "glut_wrap.h"
54#include <stdlib.h>
55#include <stdio.h>
56
57/* draw a triangle with vertices at (x1, y1), (x2, y2)
58 * and (x3, y3) at z units away from the origin.
59 */
60static void drawTriangle (GLfloat x1, GLfloat y1, GLfloat x2,
61    GLfloat y2, GLfloat x3, GLfloat y3, GLfloat z)
62{
63   glBegin (GL_TRIANGLES);
64   glVertex3f (x1, y1, z);
65   glVertex3f (x2, y2, z);
66   glVertex3f (x3, y3, z);
67   glEnd ();
68}
69
70/* draw a rectangular box with these outer x, y, and z values */
71static void drawViewVolume (GLfloat x1, GLfloat x2, GLfloat y1,
72                            GLfloat y2, GLfloat z1, GLfloat z2)
73{
74   glColor3f (1.0, 1.0, 1.0);
75   glBegin (GL_LINE_LOOP);
76   glVertex3f (x1, y1, -z1);
77   glVertex3f (x2, y1, -z1);
78   glVertex3f (x2, y2, -z1);
79   glVertex3f (x1, y2, -z1);
80   glEnd ();
81
82   glBegin (GL_LINE_LOOP);
83   glVertex3f (x1, y1, -z2);
84   glVertex3f (x2, y1, -z2);
85   glVertex3f (x2, y2, -z2);
86   glVertex3f (x1, y2, -z2);
87   glEnd ();
88
89   glBegin (GL_LINES);	/*  4 lines	*/
90   glVertex3f (x1, y1, -z1);
91   glVertex3f (x1, y1, -z2);
92   glVertex3f (x1, y2, -z1);
93   glVertex3f (x1, y2, -z2);
94   glVertex3f (x2, y1, -z1);
95   glVertex3f (x2, y1, -z2);
96   glVertex3f (x2, y2, -z1);
97   glVertex3f (x2, y2, -z2);
98   glEnd ();
99}
100
101/* drawScene draws 4 triangles and a wire frame
102 * which represents the viewing volume.
103 */
104static void drawScene (void)
105{
106   glMatrixMode (GL_PROJECTION);
107   glLoadIdentity ();
108   gluPerspective (40.0, 4.0/3.0, 1.0, 100.0);
109
110   glMatrixMode (GL_MODELVIEW);
111   glLoadIdentity ();
112   gluLookAt (7.5, 7.5, 12.5, 2.5, 2.5, -5.0, 0.0, 1.0, 0.0);
113   glColor3f (0.0, 1.0, 0.0);	/*  green triangle	*/
114   drawTriangle (2.0, 2.0, 3.0, 2.0, 2.5, 3.0, -5.0);
115   glColor3f (1.0, 0.0, 0.0);	/*  red triangle	*/
116   drawTriangle (2.0, 7.0, 3.0, 7.0, 2.5, 8.0, -5.0);
117   glColor3f (1.0, 1.0, 0.0);	/*  yellow triangles	*/
118   drawTriangle (2.0, 2.0, 3.0, 2.0, 2.5, 3.0, 0.0);
119   drawTriangle (2.0, 2.0, 3.0, 2.0, 2.5, 3.0, -10.0);
120   drawViewVolume (0.0, 5.0, 0.0, 5.0, 0.0, 10.0);
121}
122
123/* processHits prints out the contents of the selection array
124 */
125static void processHits (GLint hits, GLuint buffer[])
126{
127   GLint i;
128   GLuint j, names, *ptr;
129
130   printf ("hits = %d\n", hits);
131   ptr = (GLuint *) buffer;
132   for (i = 0; i < hits; i++) {	/*  for each hit  */
133      names = *ptr;
134      printf (" number of names for hit = %d\n", names); ptr++;
135      printf("  z1 is %g;", (float) *ptr/0x7fffffff); ptr++;
136      printf(" z2 is %g\n", (float) *ptr/0x7fffffff); ptr++;
137      printf ("   the name is ");
138      for (j = 0; j < names; j++) {	/*  for each name */
139         printf ("%d ", *ptr); ptr++;
140      }
141      printf ("\n");
142   }
143}
144
145/* selectObjects "draws" the triangles in selection mode,
146 * assigning names for the triangles.  Note that the third
147 * and fourth triangles share one name, so that if either
148 * or both triangles intersects the viewing/clipping volume,
149 * only one hit will be registered.
150 */
151#define BUFSIZE 512
152
153static void selectObjects(void)
154{
155   GLuint selectBuf[BUFSIZE];
156   GLint hits;
157
158   glSelectBuffer (BUFSIZE, selectBuf);
159   (void) glRenderMode (GL_SELECT);
160
161   glInitNames();
162   glPushName(0);
163
164   glPushMatrix ();
165   glMatrixMode (GL_PROJECTION);
166   glLoadIdentity ();
167   glOrtho (0.0, 5.0, 0.0, 5.0, 0.0, 10.0);
168   glMatrixMode (GL_MODELVIEW);
169   glLoadIdentity ();
170   glLoadName(1);
171   drawTriangle (2.0, 2.0, 3.0, 2.0, 2.5, 3.0, -5.0);
172   glLoadName(2);
173   drawTriangle (2.0, 7.0, 3.0, 7.0, 2.5, 8.0, -5.0);
174   glLoadName(3);
175   drawTriangle (2.0, 2.0, 3.0, 2.0, 2.5, 3.0, 0.0);
176   drawTriangle (2.0, 2.0, 3.0, 2.0, 2.5, 3.0, -10.0);
177   glPopMatrix ();
178   glFlush ();
179
180   hits = glRenderMode (GL_RENDER);
181   processHits (hits, selectBuf);
182}
183
184static void init (void)
185{
186   glEnable(GL_DEPTH_TEST);
187   glShadeModel(GL_FLAT);
188}
189
190static void display(void)
191{
192   glClearColor (0.0, 0.0, 0.0, 0.0);
193   glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
194   drawScene ();
195   selectObjects ();
196   glFlush();
197}
198
199/* ARGSUSED1 */
200static void keyboard(unsigned char key, int x, int y)
201{
202   switch (key) {
203      case 27:
204         exit(0);
205         break;
206   }
207}
208
209/*  Main Loop  */
210int main(int argc, char** argv)
211{
212   glutInit(&argc, argv);
213   glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
214   glutInitWindowSize (200, 200);
215   glutInitWindowPosition (100, 100);
216   glutCreateWindow (argv[0]);
217   init();
218   glutDisplayFunc(display);
219   glutKeyboardFunc(keyboard);
220   glutMainLoop();
221   return 0;
222}
223