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

## Detailed Description

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.

    /* Copyright (c) Mark J. Kilgard, 1994. */

    /*
     * (c) Copyright 1993, 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     * Unpublished-- rights reserved under the copyright laws of the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(TM) is a trademark of Silicon Graphics, Inc.
     */

    #include <GL/openglut.h>
    #include <stdlib.h>
    #include <stdio.h>

    void
    myinit(void)
    {
      glClearColor(0.0, 0.0, 0.0, 0.0);
      glDepthFunc(GL_LESS);
      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[])
    {
      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/0xffffffff);
        ptr++;
        printf(" z2 is %g\n", (float) *ptr/0xffffffff);
        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(-1);

      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);
      glutSwapBuffers();
    }

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

    static void
    key(unsigned char k, int x, int y)
    {
      switch (k) {
      case 27:  /* Escape */
        exit(0);
        break;
      default:
        return;
      }
      glutPostRedisplay();
    }

    /*  Main Loop
     *  Open window with initial window size, title bar,
     *  RGBA display mode, depth buffer, and handle input events.
     */
    int
    main(int argc, char **argv)
    {
      glutInitWindowSize(200, 200);
      glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
      glutInit(&argc, argv);
      glutCreateWindow(argv[0]);
      myinit();
      glutMouseFunc(pickRects);
      glutReshapeFunc(myReshape);
      glutDisplayFunc(display);
      glutKeyboardFunc(key);
      glutMainLoop();
      return 0;             /* ANSI C requires main to return int. */
    }

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