SELECT.C

/* 
 * (c) Copyright 1993, Silicon Graphics, Inc. 
 *               1993-1995 Microsoft Corporation 
 * 
 * ALL RIGHTS RESERVED 
 * 
 * Please refer to OpenGL/readme.txt for additional information 
 * 
 */ 
 
/* 
 *  select.c 
 *  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. 
 */ 
#include "glos.h" 
 
#include <GL/gl.h> 
#include <GL/glu.h> 
#include <GL/glaux.h> 
#include <stdio.h> 
 
void myinit(void); 
void drawTriangle (GLfloat x1, GLfloat y1, GLfloat x2, 
    GLfloat y2, GLfloat x3, GLfloat y3, GLfloat z); 
void drawViewVolume (GLfloat x1, GLfloat x2, GLfloat y1, 
    GLfloat y2, GLfloat z1, GLfloat z2); 
void drawScene (void); 
void processHits (GLint hits, GLuint buffer[]); 
void selectObjects(void); 
void CALLBACK display(void); 
 
/*  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, 0.01, 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[]) 
{ 
    int i; 
    GLint 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 %u;", *ptr); ptr++; 
        //printf (" z2 is %u\n", *ptr); ptr++; 
        //printf ("   the name is "); 
/* 
        for (j = 0; j < names; j++) { 
            //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((unsigned)-1); 
 
    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 myinit (void)  
{ 
    glDepthFunc(GL_LESS); 
    glEnable(GL_DEPTH_TEST); 
    glShadeModel(GL_FLAT); 
} 
 
void CALLBACK display(void) 
{ 
    glClearColor (0.0, 0.0, 0.0, 0.0); 
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 
    drawScene (); 
    selectObjects (); 
    glFlush(); 
} 
 
/*  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) 
{ 
    auxInitDisplayMode (AUX_SINGLE | AUX_RGB | AUX_DEPTH16); 
    auxInitPosition (0, 0, 200, 200); 
    auxInitWindow ("Selection Mode"); 
    myinit (); 
    auxMainLoop(display); 
    return(0); 
}