#include <stdlib.h>
#include <GL/glut.h>
#include <math.h>

float sealevel;
float polysize;

int seed(float x, float y) {
    static int a = 1588635695, b = 1117695901;
	int xi = *(int *)&x;
	int yi = *(int *)&y;
    return ((xi * a) % b) - ((yi * b) % a);
}

void mountain(float x0, float y0, float z0, float x1, float y1, float z1, float x2, float y2, float z2, float s)
{
	float x01,y01,z01,x12,y12,z12,x20,y20,z20;

	if (s < polysize) {
		x01 = x1 - x0;
		y01 = y1 - y0;
		z01 = z1 - z0;

		x12 = x2 - x1;
		y12 = y2 - y1;
		z12 = z2 - z1;

		x20 = x0 - x2;
		y20 = y0 - y2;
		z20 = z0 - z2;

		float nx = y01*(-z20) - (-y20)*z01;
		float ny = z01*(-x20) - (-z20)*x01;
		float nz = x01*(-y20) - (-x20)*y01;

		float den = sqrt(nx*nx + ny*ny + nz*nz);

		if (den > 0.0) {
			nx /= den;
			ny /= den;
			nz /= den;
		}

		glNormal3f(nx,ny,nz);
		glBegin(GL_TRIANGLES);
			glVertex3f(x0,y0,z0);
			glVertex3f(x1,y1,z1);
			glVertex3f(x2,y2,z2);
		glEnd();

		return;
	}

	x01 = 0.5*(x0 + x1);
	y01 = 0.5*(y0 + y1);
	z01 = 0.5*(z0 + z1);

	x12 = 0.5*(x1 + x2);
	y12 = 0.5*(y1 + y2);
	z12 = 0.5*(z1 + z2);

	x20 = 0.5*(x2 + x0);
	y20 = 0.5*(y2 + y0);
	z20 = 0.5*(z2 + z0);

	s *= 0.5;

	srand(seed(x01,y01));
	z01 += 0.3*s*(2.0*((float)rand()/(float)RAND_MAX) - 1.0);
	srand(seed(x12,y12));
	z12 += 0.3*s*(2.0*((float)rand()/(float)RAND_MAX) - 1.0);
	srand(seed(x20,y20));
	z20 += 0.3*s*(2.0*((float)rand()/(float)RAND_MAX) - 1.0);

	mountain(x0,y0,z0,x01,y01,z01,x20,y20,z20,s);
	mountain(x1,y1,z1,x12,y12,z12,x01,y01,z01,s);
	mountain(x2,y2,z2,x20,y20,z20,x12,y12,z12,s);
	mountain(x01,y01,z01,x12,y12,z12,x20,y20,z20,s);
}

void init(void) 
{
	GLfloat white[] = {1.0,1.0,1.0,1.0};
	GLfloat lpos[] = {0.0,1.0,0.0,0.0};

	glEnable(GL_LIGHTING);
	glEnable(GL_LIGHT0);

	glLightfv(GL_LIGHT0, GL_POSITION, lpos);
	glLightfv(GL_LIGHT0, GL_AMBIENT, white);
	glLightfv(GL_LIGHT0, GL_DIFFUSE, white);
	glLightfv(GL_LIGHT0, GL_SPECULAR, white);

	glClearColor (0.5, 0.5, 1.0, 0.0);
	/* glShadeModel (GL_FLAT); */
	glEnable(GL_DEPTH_TEST);

	sealevel = 0.0;
	polysize = 0.01;
}

void display(void)
{
	static GLfloat angle = 0.0;

	GLfloat tanamb[] = {0.2,0.15,0.1,1.0};
	GLfloat tandiff[] = {0.4,0.3,0.2,1.0};

	GLfloat seaamb[] = {0.0,0.0,0.2,1.0};
	GLfloat seadiff[] = {0.0,0.0,0.8,1.0};
	GLfloat seaspec[] = {0.5,0.5,1.0,1.0};


	glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
	glColor3f (1.0, 1.0, 1.0);
	glLoadIdentity ();             /* clear the matrix */
			/* viewing transformation  */
	gluLookAt (0.5, 0.0, 0.25, 0.0, 0.0, 0.0, 0.0, 0.0, 1.0);
	glRotatef(angle, 0.0, 0.0, 1.0);
	glTranslatef (-0.5, -0.5, 0.0);      /* modeling transformation */ 

	//	glutSolidTeapot(1.0);

	glMaterialfv(GL_FRONT_AND_BACK, GL_AMBIENT, tanamb);
	glMaterialfv(GL_FRONT_AND_BACK, GL_DIFFUSE, tandiff);
	glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, tandiff);
	glMaterialf(GL_FRONT_AND_BACK, GL_SHININESS, 10.0);

	mountain(0.0,0.0,0.0, 1.0,0.0,0.0, 0.0,1.0,0.0, 1.0);
	mountain(1.0,1.0,0.0, 0.0,1.0,0.0, 1.0,0.0,0.0, 1.0);

	glMaterialfv(GL_FRONT_AND_BACK, GL_AMBIENT, seaamb);
	glMaterialfv(GL_FRONT_AND_BACK, GL_DIFFUSE, seadiff);
	glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, seaspec);
	glMaterialf(GL_FRONT_AND_BACK, GL_SHININESS, 10.0);

	glNormal3f(0.0,0.0,1.0);
	glBegin(GL_QUADS);
		glVertex3f(0.0,0.0,sealevel);
		glVertex3f(1.0,0.0,sealevel);
		glVertex3f(1.0,1.0,sealevel);
		glVertex3f(0.0,1.0,sealevel);
	glEnd();

	glutSwapBuffers();
	glFlush ();

	angle += 1.0;

	glutPostRedisplay();
}

void reshape (int w, int h)
{
	glViewport (0, 0, (GLsizei) w, (GLsizei) h); 
	glMatrixMode (GL_PROJECTION);
	glLoadIdentity ();
	gluPerspective(90.0,1.0,0.01,10.0);
	glMatrixMode (GL_MODELVIEW);
}

void keyboard(unsigned char key, int x, int y)
{
   switch (key) {
		case '-':
			sealevel -= 0.01;
			break;
		case '+':
		case '=':
			sealevel += 0.01;
			break;
		case 'f':
			polysize *= 0.5;
			break;
		case 'c':
			polysize *= 2.0;
			break;
		case 27:
			exit(0);
			break;
   }
}

int main(int argc, char** argv)
{
   glutInit(&argc, argv);
   glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
   glutInitWindowSize (500, 500); 
   glutInitWindowPosition (100, 100);
   glutCreateWindow (argv[0]);
   init ();
   glutDisplayFunc(display); 
   glutReshapeFunc(reshape);
   glutKeyboardFunc(keyboard);
   glutMainLoop();
   return 0;
}