pickdepth.c

红宝书

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 * Unpublished-- rights reserved under the copyright laws of the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

/*
 * pickdepth.c
 * Picking is demonstrated in this program.  In 
 * rendering mode, three overlapping rectangles are 
 * drawn.  When the left mouse button is pressed, 
 * selection mode is entered with the picking matrix.  
 * Rectangles which are drawn under the cursor position
 * are "picked."  Pay special attention to the depth 
 * value range, which is returned.
 */
#include <GL/glut.h>
#include <stdlib.h>
#include <stdio.h>

void init(void)
{
   glClearColor(0.0, 0.0, 0.0, 0.0);
   glEnable(GL_DEPTH_TEST);
   glShadeModel(GL_FLAT);
   glDepthRange(0.0, 1.0);  /* The default z mapping */
}

/* The three rectangles are drawn.  In selection mode, 
 * each rectangle is given the same name.  Note that 
 * each rectangle is drawn with a different z value.
 */
void drawRects(GLenum mode)
{
   if (mode == GL_SELECT)
      glLoadName(1);
   glBegin(GL_QUADS);
   glColor3f(1.0, 1.0, 0.0);
   glVertex3i(2, 0, 0);
   glVertex3i(2, 6, 0);
   glVertex3i(6, 6, 0);
   glVertex3i(6, 0, 0);
   glEnd();
   if (mode == GL_SELECT)
      glLoadName(2);
   glBegin(GL_QUADS);
   glColor3f(0.0, 1.0, 1.0);
   glVertex3i(3, 2, -1);
   glVertex3i(3, 8, -1);
   glVertex3i(8, 8, -1);
   glVertex3i(8, 2, -1);
   glEnd();
   if (mode == GL_SELECT)
      glLoadName(3);
   glBegin(GL_QUADS);
   glColor3f(1.0, 0.0, 1.0);
   glVertex3i(0, 2, -2);
   glVertex3i(0, 7, -2);
   glVertex3i(5, 7, -2);
   glVertex3i(5, 2, -2);
   glEnd();
}

/*  processHits() prints out the contents of the 
 *  selection array.
 */
void processHits(GLint hits, GLuint buffer[])
{
   unsigned int i, j;
   GLuint 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");
   }
}

/*  pickRects() sets up selection mode, name stack, 
 *  and projection matrix for picking.  Then the objects 
 *  are drawn.
 */
#define BUFSIZE 512

void pickRects(int button, int state, int x, int y)
{
   GLuint selectBuf[BUFSIZE];
   GLint hits;
   GLint viewport[4];

   if (button != GLUT_LEFT_BUTTON || state != GLUT_DOWN)
      return;

   glGetIntegerv(GL_VIEWPORT, viewport);

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

   glInitNames();
   glPushName(0);

   glMatrixMode(GL_PROJECTION);
   glPushMatrix();
   glLoadIdentity();
/*  create 5x5 pixel picking region near cursor location */
   gluPickMatrix((GLdouble) x, (GLdouble) (viewport[3] - y),
                 5.0, 5.0, viewport);
   glOrtho(0.0, 8.0, 0.0, 8.0, -0.5, 2.5);
   drawRects(GL_SELECT);
   glPopMatrix();
   glFlush();

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

void display(void)
{
   glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
   drawRects(GL_RENDER);
   glFlush();
}

void reshape(int w, int h)
{
   glViewport(0, 0, (GLsizei) w, (GLsizei) h);
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   glOrtho(0.0, 8.0, 0.0, 8.0, -0.5, 2.5);
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();
}

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();
   glutReshapeFunc(reshape);
   glutDisplayFunc(display);
   glutMouseFunc(pickRects);
   glutKeyboardFunc(keyboard);
   glutMainLoop();
   return 0; 
}