/*  
In the following code we are going study Fog.

1.  Run the code as is.  Hit the 'f' key to toggle between the three types of 
fog: GL_EXP, GL_EXP2, GL_LINEAR.  If the MS-DOS window is visible, you will see
which type of fog is being calculated.

2.  The keys 'x', 'y', and 'z' can be used to rotate and view the scene from 
different angles.  Scroll through the code and take note of where each sphere
is being rendered.  What happens if each sphere is rendered in the same z=-1.0
plane?

3.  Change the glHint from GL_DONT_CARE to GL_FASTEST then GL_NICEST.

4.  Try different values for the GL_FOG_DENSITY.
*/

#include <GL/glut.h>
#include <cmath>
#include <stdlib.h>
#include <stdio.h>

static GLint fogMode;

GLfloat xangle=0;
GLfloat yangle=0;
GLfloat zangle=0;

static void init(void) 
{
	GLfloat position[] = { 0.5 , 0.5 , 3.0 , 0.0 };

	glEnable(GL_DEPTH_TEST);

	glLightfv(GL_LIGHT0 , GL_POSITION , position);
	glEnable(GL_LIGHTING);
	glEnable(GL_LIGHT0);

	{
		GLfloat mat[3] = {0.1745,0.01175,0.01175};
		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);
	}

	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);
		glFogf(GL_FOG_START, 1.0);
		glFogf(GL_FOG_END, 5.0);
	}

	// Fog Color
	glClearColor(0.5 , 0.5 , 0.5 , 1.0);

}

static void renderSphere(GLfloat x, GLfloat y, GLfloat z)
{
	glPushMatrix();
	glTranslatef(x, y, z);
	glutSolidSphere(0.4, 16, 16);
	glPopMatrix();
}

void display(void)
{
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

	glLoadIdentity();
	glRotatef(xangle, 1, 0, 0);
	glRotatef(yangle, 0, 1, 0);
	glRotatef(zangle, 0, 0, 1);

	// render 5 spheres, at different distances, to sample the effects of fog
	renderSphere(-2.0 , -0.5 , -1.0);
	renderSphere(-1.0 , -0.5 , -2.0);
	renderSphere( 0.0 , -0.5 , -3.0);
	renderSphere( 1.0 , -0.5 , -4.0);
	renderSphere( 2.0 , -0.5 , -5.0);
	glFlush();
}

void reshape( int w , int h )
{
	glViewport(0 , 0 , (GLsizei) w , (GLsizei) h);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	if (w <= h)
		glOrtho( -2.5, 2.5,
		-2.5*(GLfloat)h/(GLfloat)w, 2.5*(GLfloat)h/(GLfloat)w,
		-10.0 , 10.0 );
	else
		glOrtho( -2.5*(GLfloat)h/(GLfloat)w, 2.5*(GLfloat)h/(GLfloat)w,
		-2.5, 2.5,
		-10.0 , 10.0 );
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
}

void keyboard(unsigned char key , int x, int y)
{
	switch (key) {
		case 'f':
		case 'F':
			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");
			}
			else if (fogMode == GL_LINEAR) {
				fogMode = GL_EXP;
				printf("Fog mode is GL_EXP\n");
			}
			glFogi(GL_FOG_MODE, fogMode);
			glutPostRedisplay();
			break;
		case 'q':
		case 'Q':
			exit(0);
			break;
		case 'x':
                xangle+=5;
				glutPostRedisplay();
                break;
        case 'y':
                yangle+=5;
				glutPostRedisplay();
                break;
        case 'z':
                zangle+=5;
				glutPostRedisplay();
                break;
		default:
			break;
	}
}

int main(int argc, char** argv)
{
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
	glutInitWindowSize(500, 500);
	glutCreateWindow(argv[0]);
	init();
	glutReshapeFunc(reshape);
	glutKeyboardFunc(keyboard);
	glutDisplayFunc(display);
	glutMainLoop();
	return 0;
}