/*
 * (c) Copyright 1993, Silicon Graphics, Inc.
 *               1993, 1994 Microsoft Corporation
 *
 * ALL RIGHTS RESERVED
 *
 * Please refer to OpenGL/readme.txt for additional information
 *
 */

/*
 *  fog.c
 *  This program draws 5 red teapots, each at a different 
 *  z distance from the eye, in different types of fog.  
 *  Pressing the left mouse button chooses between 3 types of 
 *  fog:  exponential, exponential squared, and linear.  
 *  In this program, there is a fixed density value, as well 
 *  as fixed start and end values for the linear fog.
 */
#include "glos.h"

#include <GL/gl.h>
#include <GL/glu.h>
#include <math.h>
#include <GL/glaux.h>
#include <stdio.h>

void myinit(void);
void renderRedTeapot (GLfloat x, GLfloat y, GLfloat z);
void CALLBACK cycleFog (AUX_EVENTREC *event);
void CALLBACK myReshape(GLsizei w, GLsizei h);
void CALLBACK display(void);

GLint fogMode;

void CALLBACK cycleFog (AUX_EVENTREC *event)
{
    if (fogMode == GL_EXP) {
    fogMode = GL_EXP2;
    //printf ("Fog mode is GL_EXP2\n");
    }
    else if (fogMode == GL_EXP2) {
    fogMode = GL_LINEAR;
    //printf ("Fog mode is GL_LINEAR\n");
    glFogf (GL_FOG_START, 1.0);
    glFogf (GL_FOG_END, 5.0);
    }
    else if (fogMode == GL_LINEAR) {
    fogMode = GL_EXP;
    //printf ("Fog mode is GL_EXP\n");
    }
    glFogi (GL_FOG_MODE, fogMode);
}

/*  Initialize z-buffer, projection matrix, light source, 
 *  and lighting model.  Do not specify a material property here.
 */
void myinit(void)
{
    GLfloat position[] = { 0.0, 3.0, 3.0, 0.0 };
    GLfloat local_view[] = { 0.0 };

    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LESS);

    glLightfv(GL_LIGHT0, GL_POSITION, position);
    glLightModelfv(GL_LIGHT_MODEL_LOCAL_VIEWER, local_view);

    glFrontFace (GL_CW);
    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);
    glEnable(GL_AUTO_NORMAL);
    glEnable(GL_NORMALIZE);
    glEnable(GL_FOG);
    {
    GLfloat fogColor[4] = {0.5, 0.5, 0.5, 1.0};

    fogMode = GL_EXP;
    glFogi (GL_FOG_MODE, fogMode);
    glFogfv (GL_FOG_COLOR, fogColor);
    glFogf (GL_FOG_DENSITY, 0.35);
    glHint (GL_FOG_HINT, GL_DONT_CARE);
    glClearColor(0.5, 0.5, 0.5, 1.0);
    }
}

void renderRedTeapot (GLfloat x, GLfloat y, GLfloat z)
{
    float mat[3];

    glPushMatrix();
    glTranslatef (x, y, z);
    mat[0] = 0.1745; mat[1] = 0.01175; mat[2] = 0.01175;    
    glMaterialfv (GL_FRONT, GL_AMBIENT, mat);
    mat[0] = 0.61424; mat[1] = 0.04136; mat[2] = 0.04136;   
    glMaterialfv (GL_FRONT, GL_DIFFUSE, mat);
    mat[0] = 0.727811; mat[1] = 0.626959; mat[2] = 0.626959;
    glMaterialfv (GL_FRONT, GL_SPECULAR, mat);
    glMaterialf (GL_FRONT, GL_SHININESS, 0.6*128.0);
    auxSolidTeapot(1.0);
    glPopMatrix();
}

/*  display() draws 5 teapots at different z positions.
 */
void CALLBACK display(void)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    renderRedTeapot (-4.0, -0.5, -1.0);
    renderRedTeapot (-2.0, -0.5, -2.0);
    renderRedTeapot (0.0, -0.5, -3.0);
    renderRedTeapot (2.0, -0.5, -4.0);
    renderRedTeapot (4.0, -0.5, -5.0);
    glFlush();
}

void CALLBACK myReshape(GLsizei w, GLsizei h)
{
    h = (h == 0) ? 1 : h;
    glViewport(0, 0, w, h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    if (w <= (h*3))
    glOrtho (-6.0, 6.0, -2.0*((GLfloat) h*3)/(GLfloat) w, 
        2.0*((GLfloat) h*3)/(GLfloat) w, 0.0, 10.0);
    else
    glOrtho (-6.0*(GLfloat) w/((GLfloat) h*3), 
        6.0*(GLfloat) w/((GLfloat) h*3), -2.0, 2.0, 0.0, 10.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity ();
}

/*  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, 450, 150);
    auxInitWindow ("Fog");
    auxMouseFunc (AUX_LEFTBUTTON, AUX_MOUSEDOWN, cycleFog);
    myinit();
    auxReshapeFunc (myReshape);
    auxMainLoop(display);
    return(0);
}
