/*
 * (c) Copyright 1993, Silicon Graphics, Inc.
 *               1993, 1994 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);
}
